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ANNEX 8
Size management

AS MENTIONED IN SEVERAL SECTIONS of this manual, freshwater prawns do not grow at an even rate (Annex 8, Figure 1). This makes the management of size an essential component of the efficient husbandry that is needed to ensure their successful farming. A considerable volume of knowledge about the different (male) morphotypes which play a part in the phenomenon of uneven growth has been gained since the previous FAO manual on freshwater prawn farming was written. The topic has been reviewed in depth by Karplus, Malecha and Sagi (2000), from which the material in this annex has been derived. The main purpose of Sections 1-3 in this annex is to provide an introduction to the scientific background; it is necessary to study this to understand the phenomenon of size distribution and management. Practical advice on management contained in the main text of the manual has taken these factors into account. Section 4 of this annex provides a check-list of the various techniques which it is essential that farmers apply to get the maximum output of marketable prawns.

1. Major male morphological characteristics

Firstly, it is necessary to understand what is meant by the various morphotypes. Three major morphotypes have been described for sexually mature male M. rosenbergii (Annex 8, Figure 2). The most immediately distinctive feature is the size and colour of the claws, and the robustness of their spines:

There are also a number of intermediary forms between these major morphotypes. The transition from the small male (SM) to the orange claw (OC) morphotype is gradual. The OC is therefore sometimes referred to as the strong orange claw (SOC), and an intermediate stage between these two forms, the weak orange claw male (WOC), has been recognized in research work. Another intermediate form, this time between the orange claw (OC) and the blue claw (BC) is known as the transforming orange claw (TOC); this is the last stage of the SOC male before it transforms into the BC male, as described later in this annex.

Karplus, Malecha and Sagi (2000) also describe some other external features which can be used to delineate the various morphotypes, such as the length and orientation of the spines on the claws, but these are less immediately obvious than claw colour and size. There are also a number of internal morphological and physiological differences, as well as differences in moult frequency. SM have relatively large testes that both produce and store sperm. The testes of BC serve mainly as a sperm reservoirs. The three orange claw male forms (WOC, SOC and TOC) represent a series of gradual changes between SM and BC. Firstly, the abundance of mature sperm found in the testes of SM declines and almost disappears in the early OC stages. At the same time, the rate of production of spermatocytes (cells from which spermatozoa arise) increases as the SM moults into the OC phase. The OC phase is also characterized by frequent moulting. Another differential feature is the size (weight) of the midgut glands, especially the hepatopancreas. The hepatopancreas weight of the rapidly growing SOC is much greater than in all other morphotypes. The slow-growing SM and BC have the lowest relative midgut gland weight, while the WOC and the TOC males have intermediate values.

ANNEX 8, FIGURE 2
The major male morphotypes of Macrobrachium rosenbergii are called blue claw (BC), orange claw (OC), and small male (SM) (Israel)

SOURCE: ASSAF BARKI, REPRODUCED FROM NEW AND VALENTI (2000) WITH PERMISSION FROM BLACKWELL SCIENCE

2. Behaviour

The behavioural characteristics of the morphotypes described above are of essential importance in the management of freshwater prawn grow-out facilities. BC males are aggressive, dominant and ‘territorial’, OC males are aggressive, subdominant and ‘non-territorial’, and SM males are submissive and ‘non-territorial’.

FIGHTING (AGONISTIC) BEHAVIOUR

The fighting behaviour of the three male morphotypes differs as males follow the developmental pathway from SM through OC to BC. There is less physical contact and fewer displays of claw position and movement occur in SM than in OC and BC. As claw size increases there is an increased risk of severe injuries caused by claws during interactions amongst OC and BC prawns. Male prawns have a hierarchical relationship. BC males are dominant over OC males which, in turn, are dominant over SM. Interactions between BC males are often only for show, with little physical contact. Those between BC and OC males involve more physical contact but BC males generally use threat displays and mere approaches in their relationships with SM. BC and OC males with equal claw size are evenly matched but a BC with larger claws than an OC, even if the OC is much larger, has an advantage. The dominance of BC over OC seems to confer priority of access to preferred areas (e.g. shaded protected crevices) but true territoriality (defending a fixed exclusive area to keep intruders out) has not yet been adequately demonstrated. However, laboratory studies have shown that competitors are evicted from the vicinity of a limiting resource, such as shelter, food, and receptive females.

MATING BEHAVIOUR

Females approach males 2 to 3 days before their pre-mating moult. At first the female is chased away but later, after several hours of persistence, is allowed to remain near the male. About a day before the pre-mating moult the female is already totally accepted by the male, positioned below it or between its long second pair of claws. As a result of this early pair bonding, fertilisation can occur from several minutes to half an hour after moulting. It has been reported to occur up to nearly 22 hours later than the moult but this has been because researchers were pairing the males and females themselves, rather than allowing the natural bonding described above to occur. All three male morphotypes have similarly high rates of fertilising receptive females. Despite the fact that the spermatophores of SM are about half the size of those of BC males, the number of viable embryos following mating is dependent only on the female size, not on the type of male morphotype.

Males do not attack or injure the females that they have just fertilized. BC tend to guard the female for two or three days following mating, by which time the female’s exoskeleton is hard enough to withstand attacks by other prawns. However, OC do not appear to groom or protect the females. There are reports of injuries inflicted by OC on females during this period (especially when more than one OC is present) but the information is, at present, conflicting. Small males have been observed to mate with females by sneaking between a receptive female and her guarding BC male. A single SM has little or no chance to gain access to a receptive female guarded by a BC male. However, SM mating can be achieved when there are three or more SM present; while the BC is chasing away some of the runts, the female remains unprotected. Occasionally, following their pre-mating moult, females have been observed with several spermatophores attached to their sperm receptacle. There is some evidence that females are more attracted (through chemoreception) to BC and are more aggressive towards other male morphotypes. However, unfertilized females quickly lose all their eggs, which may be the reason why females that have undergone the pre-mate moult cooperate during mating with any of the male morphotypes.

3. Importance of population structure in freshwater prawn farming

The characteristics of size distribution in freshwater prawns (Annex 8, Figure 1) has been mentioned many times in this manual. This section of the annex describes how various factors affect the size distribution of the prawns in your ponds.

THE EFFECT OF THE SEX RATIO

The proportion of females under grow-out conditions tends to be greater than males, possibly for the following reasons:

Since the highest prices are generally obtainable for the largest animals, a preponderance of females in a population may seem to be a disadvantage at first glance. It would appear to indicate that there would be a strong incentive to rear all-male populations of prawns. However, the effect of density on average weight is more extremely pronounced in all-male, compared to all-female populations. The use of all-male populations would therefore not remove the need to manage size variation and harvesting procedures very carefully. If maximizing the total weight of prawns produced per hectare is the main goal, the rearing of all-female populations at very high densities would be sensible. However, if maximizing the income from the pond is the main goal, proper management of mixed-sex or all-male populations would be best, since the larger-sized prawns normally have the greatest unit value. Manual sexing has been done on an experimental scale but this requires extremely skilful workers and is very labour-intensive. It is likely that commercial preparations of the sex-controlling androgenic hormone to sex-reverse the broodstock used to generate monosex populations will become available in future.

THE EFFECT OF DENSITY

The proportions of the various male morphotypes change significantly with density (Annex 8, Figure 3). High density results in a larger proportion of SM. The frequency of the large BC males is highest at low densities. At high densities many prawns are in close contact with BC males, which inhibit their growth.

THE EFFECT OF UNEVEN MALE GROWTH RATE

Newly metamorphosed postlarvae are relatively even in size but size variation soon becomes noticeable. Individual prawns grow at different rates. This is known as heterogeneous individual growth (HIG). Some exceptionally fast-growing individuals (sometimes called ‘jumpers’) may become up to 15 times larger than the population mode within 60 days after metamorphosis, forming the leading tail of the population distribution curve. Jumpers became obvious within two weeks after metamorphosis. Slow-growing prawns (laggards) only become apparent later, about 5 weeks following metamorphosis. It has been suggested that growth suppression in laggards depends upon the presence of the larger jumpers. Male jumpers develop mainly into BC and OC males, while laggards develop mainly into small males.

Once this specific growth pattern has been established, juvenile prawns continue to show different growth patterns, even when they are isolated. Many studies have been conducted on the effects (on harvest production and average animal weight) of grading prawns into different fractions depending on size but are outside the scope this manual to record. For further reading on this topic see the review by Karplus, Malecha and Sagi (2000). This research has provided important clues towards improved management of grow-out populations in freshwater prawn farming and form some of the background for the comments on grading in this manual.

THE SOCIAL CONTROL OF GROWTH

Social interactions between freshwater prawns are extremely important in regulating growth. In freshwater prawns the most important social interactions are the growth enhancement of OC males (what is known as the ‘leapfrog’ growth pattern) and the growth suppression of SM by BC males.

Growth enhancement of orange claw males

The change of OC males into BC males is sometimes called a metamorphosis because the differences between these morphotypes are so dramatic. An OC metamorphoses into a BC after it becomes larger than the largest BC in its vicinity (Annex 8, Figure 4). As a new BC male it then delays the transition of the next OC to the BC morphotype, causing it in turn to attain a larger size following its metamorphosis. The newly transformed BC is larger (sometimes much larger) than the largest BC previously present. This is known as the ‘leapfrog’ growth pattern, because the weight of one type of animal leaps over another.

BC males dominate OC males, regardless of their size, probably because of their larger claws. A prawn that has metamorphosed into a BC male and is larger than any other BC in its vicinity (following the ‘leapfrog’ growth pattern) becomes the most dominant prawn in the vicinity until it is overtaken by another prawn metamorphosing from OC to BC. The ‘leapfrog’ growth pattern results in the gradual descent in the social rank of existing BC males. When a new and larger BC appears on the scene, the ‘social ranking’ of all BC males present before that event fall.

Growth suppression of small males

The growth of runts (SM) is stunted by the presence of BC males. Food conversion efficiency seems to be the major mechanism controlling this growth suppression in runts. Runts have poorer (higher FCR) feed efficiency when BC males are present. This seems to be governed by physical proximity; the phenomenon has not been demonstrated when these two types of prawns are separated, even when they are in the same water system and can see each other (i.e. chemoreception and sight are not factors).

As noted earlier in this annex, SM are sexually active. While they stay small they attract less aggression from dominant BC males (which are busier interacting with OC males) and are probably less vulnerable to cannibalism since they can shelter in small crevices. Being small and highly mobile, runts can find food on the bottom before being chased away by larger prawns, whether they be males or females. If BC males are removed from the population, some runts will increase their growth rate, and transform into OC males and, finally into BC males, following the normal ‘leapfrog’ growth pattern. This highlights the importance of regular cull-harvesting.

4. Managing grow-out in the light of heterogeneous individual growth (HIG)

Several important characteristics of freshwater prawns that affect the potential harvest from grow-out have been described above. These create various management options; a check-list of those procedures is provided below. The first three techniques have been described in the main text of this manual. The final technique (monosex culture) is a possible future development and is not part of the current manual. In grow-out management:

ANNEX 9
Farm-made pond feeds

THIS ANNEX PROVIDES a very brief introduction to farm-made grow-out feeds and their use for freshwater prawns. Further reading on this topic is provided in New (1987) and New, Tacon and Csavas (1995).

1. Feed preparation

The following general instructions are for the preparation of diets, which may be fed moist or dried.

  1. Mix all your dry ingredients (except vitamin mix, if used) thoroughly, preferably in a mechanical mixer.
  2. Add your vitamin mix, if your formula contains one, and remix as in No. 1 above.
  3. Add any liquid ingredient (such as fish oil) or any wet materials (such as chopped trash fish). [Note of caution: commercially processed shrimp by-products, such as shrimp meal and shrimp head meal, are very valuable from a nutritional point of view in feeds for freshwater prawns. There is no danger that such ingredients will cause disease problems (Flegel, 2001). However, the use of raw (unprocessed) shrimp or prawn wastes, such as prawn heads, may introduce viruses (e.g. WSSV) into your farmed animals. Although this may not cause any visible symptoms it may make them carriers of the disease for other crustaceans.]
  4. Remix all your ingredients thoroughly.
  5. You will now need to add up to 30-35% of water. The exact quantity depends on the moisture of the ingredients. You will need to add enough water to produce a very thick paste. Add water a little at a time and test the mixture. It is easy to add more water (but not possible to remove it if you add too much at first!). You can test the consistency (stickiness) of the diet by squeezing it within your clenched hand. If the ‘sausage’ of mixed diet (consistency of bread dough) which emerges from your fist between your first finger and your thumb is too crumbly, you need to add more water. If it runs out like a liquid, you have already added too much water!
  6. Continue mixing. You can help to mix your ingredients thoroughly by passing the mixture through the coarse die of a meat mincer (see No. 7 below). This works well and also helps to bind the diet together.
  7. You can now shape the mixed diet into small balls or discs by hand. However, it is best if you extrude the mixed diet through a meat mincer, this time using small die holes (1/8-in diameter) to produce a well-bound spaghetti-like material, which breaks easily into pellets when dried. Annex 9, Figures 1 and 2 show this process.
  8. You can feed your mixed diet as it is (in a moist form) if you can use it on the same day as you make it. Alternatively, you can stir the extruded ‘spaghetti’ to form 1-2 cm long pellets and sun-dry them for later use. Drying on a concrete surface in direct sunlight for six hours (Annex 9, Figure 3) may be sufficient to reduce the moisture content of the pellets to a level (about 10-12%) at which they can be stored without excessive deterioration. Dried feed takes less space and is much easier to transport to the pond (Annex 9, Figure 4) and to feed. A simple solar dryer (Annex 9, Figure 5) can be constructed for drying pellets during the monsoon season; however, this is difficult to use if you are producing a lot of feed. Many farms find it more feasible to choose days on which the weather is forecast to be dry to manufacture and dry their feed. Others find that the feed can be collected up from the concrete drying surface if a rain cloud approaches and then put out again when the sun returns. This sounds difficult to do but the author of this manual has observed it being done! Whatever, method you choose, it is important that the feed is dried in as short a time as possible to prevent fungal growth.
  9. Dried pellets can be stored up to 2-3 months. You must store them in the coolest conditions possible. It is essential to keep them dry and to protect them from rats and other animals during storage.

ANNEX 9, Figure 1
Some farmers make their own equipment for extruding farm-made feeds (Thailand); this photo shows the tray where the mixed feed is pushed into the grinder, whose die plate is at the far side (not visible)

SOURCE: HASSANAI KONGKEO

2. Feed formulae

Some examples of feed formulae for the pond rearing of freshwater are given in Annex 9, Tables 1-7. Please note that these formulae are only examples; many other feeds have been used, or are possible, depending on the availability of raw materials. These examples have been extracted from D’Abramo and New (2000), where the original references are cited. Diets 1-4 are practical feeds that have actually been used in freshwater prawn grow-out. Diets Nos. 5-12 have been used in experimental work.

ANNEX 9, Figure 2
In this photo, freshwater prawn feed is being extruded from the die plate of a meat chopper (Thailand)

SOURCE: MICHAEL NEW

ANNEX 9, Figure 3
Farm-made feeds need to be dried if not fed directly after manufacture; this can be done by spreading the feed out on concrete or on trays for sun-drying (Brazil)

SOURCE: DENIS LACROIX

ANNEX 9, figure 4
Feed that has been extruded through a mincer and sun-dried is easy to transport to the ponds (Thailand)

SOURCE: HASSANAI KONGKEO

ANNEX 9, TABLE 1
Farm-made grow-out feeds No. 1 and No. 2

INGREDIENT

FEED NO. 1

FEED NO. 2

 

 

 

(kg)

(%)

(kg)

(%)

Trash fish

100.0

29.61

100.0

28.35

Soybean meal

40.0

11.84

40.0

11.34

Fish meal

20.0

5.92

10.0

2.84

Corn meal

80.0

23.70

80.0

22.68

Di-calcium phosphate

2.0

0.59

2.0

0.57

Oxytetracycline*

0.2

0.06

-

-

Vitamin and mineral mix**

0.5

0.15

0.5

0.14

Vitamin C

-

-

0.2

0.06

Broken rice (boiled)***

30.0

8.88

30.0

8.51

Chicken layers feed

50.0

14.81

60.0

17.01

Piglet feed

15.0

4.44

15.0

4.25

Shrimp shell meal

-

-

15.0

4.25

Totals (approximate)

337.7

100.00

352.7

100.00

* PLEASE NOTE THE CAUTIONS ON THE REGULAR USE OF ANTIBIOTICS IN THE TEXT OF THIS MANUAL.
** NO DETAILS AVAILABLE.
*** WEIGHT BEFORE BOILING.

ANNEX 9, TABLE 2
Farm-made grow-out feed No. 3

INGREDIENT

(kg)

(%)

Trash fish

100

44.2

Chicken feed

60

26.6

Broken rice

30

13.3

Fish meal

20

8.8

Piglet concentrate*

15

6.6

Premix**

1

0.5

Total

226

100.0

* COMPOSITION UNKNOWN.
** A LOCALLY AVAILABLE VITAMIN MIXTURE BEING SOLD FOR FRESHWATER PRAWNS. IT WAS STATED TO CONTAIN VITAMINS A, D, C, AND E, AND AN UNSPECIFIED ANTIBIOTIC (OXYTETRACYCLINE ?) [SEE NOTE BELOW PREVIOUS TABLE]. THE MANUFACTURER SUGGESTED A VITAMIN MIX INCLUSION RATE OF 0.5-1.0%.

ANNEX 9, TABLE 3
Farm-made grow-out feed No. 4

INGREDIENT

(%)

Fish meal*

22.5

Fresh trash fish

10.0

Rice bran

20.0

Ground rice

17.5

Sesame cake

12.5

Fish oil

2.5

Sago (palm starch)

7.0

Cane molasses

6.5

Animal grade Vitamin C**

0.5

Water

1.0

Total

100.0

* AT LEAST 50% PROTEIN.
** NO DETAILS AVAILABLE. NOTE: NO OTHER SUPPLEMENTARY VITAMINS ADDED.

ANNEX 9, TABLE 4
Farm-made grow-out feed No. 5 and No. 6

INGREDIENT

FEED NO. 5(%)

FEED NO. 6(%)

Shrimp meal

31.6

-

Fish meal

-

23.0

Soybean meal (44% crude protein)

34.4

32.6

Maize meal

14.2

17.5

Alfalfa meal

10.3

13.2

Fish oil

4.7

3.7

Di-calcium phosphate

3.1

4.9

Monosodium phosphate

0.7

4.1

Premix*

0.4

0.4

Iodized salt

0.5

0.5

Binder*

0.1

0.1

Totals

100.0

100.0

* NO DETAILS AVAILABLE.

ANNEX 9, TABLE 5
Farm-made grow-out feed No. 7 and No. 8

INGREDIENT

FEED NO. 7(%)

FEED NO. 8(%)

Fish meal

20.0

-

Shrimp head meal

-

30.0

Soybean meal

9.0

4.0

Rice bran

45.0

35.0

Coconut oil cake

20.0

20.0

Tapioca (cassava starch)

5.0

9.0

Pfizer premix A*

1.0

1.0

Agar

-

1.0

Totals

100.0

100.0

* NO DETAILS AVAILABLE.

ANNEX 9, TABLE 6
Farm-made grow-out feed No. 9 and No. 10

INGREDIENT

FEED NO. 9(%)

FEED NO. 10(%)

Soybean meal (44% CP)

22.4

20.7

Fish meal

20.0

20.0

Maize meal

18.6

6.5

Dried yeast

10.0

10.0

Wheat meal

10.0

10.0

Wheat bran

-

8.8

Grass meal (Bracharia

 

 

purpurescens)

12.7

15.0

Di-calcium phosphate

3.8

3.4

Lime (calcite*)

0.1

0.4

Fish oil

1.4

4.3

Premix**

0.5

0.4

Iodized salt

0.5

0.5

Totals

100.0

100.0

* CRYSTALLINE CaCO3
** NO DETAILS AVAILABLE.

ANNEX 9,TABLE 7
Farm-made grow-out feed No. 11 and No. 12

INGREDIENT

FEED NO. 11(%)

FEED NO. 12(%)

Fish oil

3.0

3.0

Shrimp meal

25.0

10.0

Fish meal

10.0

4.0

Peanut meal (groundnut)

5.0

2.0

Soybean meal

5.0

2.0

Broken rice

25.5

39.0

Rice bran

25.5

39.0

Guar gum

1.0

1.0

Totals

100.0

100.0

NOTE: NO VITAMIN OR MINERAL MIX

ANNEX 10
Basic code for introductions

ANNEX IS DERIVED, with acknowledgements, from part II of a draft framework for the responsible use of introduced species that was prepared for EIFAC by Bartley, Subasinghe and Coates (1999).

The basic code for introductions applies to the intentional movement of aquatic species in fisheries, biological control, aquaculture, and for research. Therefore, someone, some organization, some private business, or some government agency (referred to below as ‘the entity’) must knowingly engage in the act of transporting the species. Guidelines and policy concerning species introduced inadvertently through ballast water or on ship’s hulls are addressed elsewhere, for example by the International Maritime Organization. Development projects that involve geographic changes, such as river diversion, dredging of canals to connect distinct water bodies, etc. also may involve the subsequent introduction of exotic species and therefore this framework could also be used in the review and evaluation of those projects.

The basic code contains the requirements that:

  1. the entity moving an exotic species develop a proposal, that would include location of facility, planned use, passport information, and source of the exotic species;
  2. an independent review that evaluates the proposal and the impacts and risk/benefits of the proposed introduction, e.g. pathogens, ecological requirements/interactions, genetic concerns, socio-economic concerns, and local species most affected, would be evaluated;
  3. advice and comment are communicated among the proposers, evaluators and decision makers and the independent review advises to either accept, refine, or reject the proposal so that all parties understand the basis for any decision or action, thus proposals can be refined and review panel can request additional information on which to make their recommendation;
  4. if approval to introduce a species is granted, quarantine, containment, monitoring, and reporting programmes are implemented; and
  5. the ongoing practice of importing the (formerly) exotic species becomes subject to review and inspection that check the general condition of the shipments, e.g. checking that no pathogens are present, that the correct species is being shipped, etc.

The Code is general and can be adapted to specific circumstances and resource availability, but it should not lose any of the above requirements nor should it lose the rigour at which the requirements are applied. For example, a regulatory agency may require a proposal to contain a first evaluation of the risk/benefits and this evaluation would then be forwarded to an independent review or advisory panel; or the advisory panel could make the first evaluation of a proposal. Similarly, States may require quarantine procedures to be explicitly described in the proposal before approval is granted.

ANNEX 11
Glossary of terms, abbreviations and conversions

Terms

THE FIRST SECTION OF THIS GLOSSARY defines unfamiliar terms used in this manual. The definitions are intended to make the terms understandable to the novice rather than to the biologist.

Abdomen:

commonly referred to as the ‘tail’ of prawns, this is the area containing segments from which the swimming appendages originate. See Table 1 of the main text for details.

Agonistic:

fighting, combative behaviour.

Artemia:

scientific name for brine shrimp.

Bacteria:

microscopic single-cell organisms of a kind which can cause disease.

Bank:

the elevated rim of a pond. Also called embankment, dyke (dike), berm or bund.

Batch culture:

a system of rearing prawns involving the total harvest, by seining or draining or both, at a certain interval after stocking (see Box 15). The ponds are then drained before re-stocking.

Benthic:

organisms living on the bottom of the pond; opposite of planktonic.

Berm:

see Bank.

Berried:

egg carrying.

Brine shrimp:

a small crustacean whose larvae are used to feed larval prawns.

Brood chamber:

an area formed beneath the abdomen of the mature female by the expansion of the pleura, in which the fertilized eggs are carried before hatching. In this area the eggs are oxygenated by movement of the pleopods.

BSE:

bovine spongiform encephalopathy, a serious disease of ruminants, which seems to be associated with the incidence of a similar disease in humans. Colloquially known as mad cow disease.

Buffer:

a substance or substances which resist or counteract changes in the acidity or alkalinity of water.

Bund:

see Bank.

Carapace:

a dorsal cover which obscures the division between the true head (cephalon) and the thorax (jointly known as the cephalothorax) of prawns.

Caridean:

a crustacean which belongs to one of the two main groups (infraorders; sections) which form the suborder Natantia of the order Decapoda. The group is called the Caridea; thus these crustaceans are known as carideans. Within this infraorder (Caridea) the family of main importance to aquaculture is the Palaemonidae, which, in addition to containing some marine prawns (e.g. Palaemon serratus), contains most of the commonly farmed freshwater prawns belonging to the genus Macrobrachium (e.g. Macrobrachium amazonicum, M. malcolmsonii, M. nipponense and M. rosenbergii).

Cephalon:

part of the area under the carapace. Contains the segments from which the eyes, antennae, and three other pairs of appendages originate. See Table 1 of the main text for details.

Chela:

claw

Chelae:

plural of chela.

Chelating:

the action of a chelator.

Chelator:

a substance which binds ions and holds them longer in suspension, thus (for example) making nutrients available to algae longer. Chelators also sequester (bind) heavy metals that may have entered the system from exterior sources, thus reducing the toxicity that they may have for prawn larvae. In greenwater systems both chelating actions would be valuable; in clearwater systems, it is the reduction of toxicity that is the most likely to cause the beneficial effect.

Cheliped:

literally a leg with a claw on it. Strictly, all the pereiopods have claws on them and are therefore chelipeds. However, only on the first two pairs are the claws (chelae) formed into pincers. In practice, the word cheliped is often only applied to the legs with the largest pincers (in freshwater prawns these are the longest legs, the second pereiopods).

Clearwater:

larval rearing water which does not contain green planktonic algae.

Combined system of
culture:

an intermediate form of culture between batch and continuous culture, on which the grow-out and harvesting sections of this manual are based (see Box 15).

Continuous culture:

a system of rearing prawns in ponds which involves continuouspond operation (see Box 15). Ponds are not regularly drained for harvesting, nor completely harvested. The larger animals are regularly removed by seine net for marketing, leaving the smaller ones to grow on. The ponds are regularly restocked with postlarvae or juveniles

Count:

this term, used by shrimp buyers, refers to the number of prawns or prawn tails per unit weight. When using this term, it is important to state whether shell-on/head-on, shell-on tails or peeled tails are being described.

Crustacea:

group of animals including shrimp and prawns, lobsters, and crabs.

Decapsulation:

the removal of the hard outer layer (shell) of Artemia cysts.

Dike:

see Bank.

DO2:

dissolved oxygen content (of water). Sometimes reported as ppm and sometimes as percent of saturation level. In this manual, ppm has been used.

Dorsal:

upper.

Dyke:

see Bank.

Endopod:

anatomical term referring to the inner part of the end of an appendage.

Epilimnion:

upper layer of water in a stratified lake or reservoir.

Exopod:

anatomical term referring to the outer part of the end of an appendage.

Exoskeleton:

the outer hard coat of crustaceans, often referred to as the shell.

Exuvia:

the cast shell (exoskeleton) after moulting.

Feed Conversion

the amount of food necessary to produce one unit weight (wet) of

Efficiency (FCE):

prawns. For example, if a pond produces 1 250 kg of prawns and 3 200 kg of food were used during the rearing period, the feed conversion efficiency is: FCE = 3 200 ÷ 1 250 = 2.56. It follows, therefore, that the lower the FCE is, the better the efficiency (of conversion into final product) of the food is. The FCE of wet feeds will be much higher than that of dry feeds because of the difference in moisture content. To directly compare two feeds with different moisture contents, it is necessary to convert the different feed conversion efficiencies to a standard moisture content or to bring the relative cost of the feeds into consideration. The latter option is more meaningful. For example, let us suppose that Feed A has an FCE of 2.8 and a cost of US$ 492/mt. On the other hand, Feed B has an FCE of 6.9 and a cost of US$ 215/mt. Which is the ‘better’ feed from the farmers’ point of view? To produce one ton of prawn using Feed A would cost US$ 492 x 2.8 = US$ 1 377.60; using Feed B it would cost US$ 215 x 6.9 = US$ 1 483.50. Feed A is therefore cheaper to use, even though its unit price is more than twice than that of Feed B.

Feed Conversion

this is the same as feed conversion efficiency, except that it is

Ratio:

written as a ratio (FCR), i.e. a feed conversion efficiency of 2.8 is written as a feed conversion ratio of 2.8:1. This means 2.8 kg of food is necessary to produce 1 kg of prawns live weight. The two terms are frequently used synonymously. For example, you may often see an expression such as ‘the FCE of the diet was 2.8:1’.

Genital pores:

the openings of the reproductive organs to the exterior of the animal. In males they are between the fifth pair of pereiopods and in females between the third pair of pereiopods.

Gill chamber:

the area at the sides of the ‘head’ of the prawn that contains the gills through which the prawn takes oxygen from the water and releases carbon dioxide during respiration.

Greenwater:

larval rearing water with an induced density of green planktonic algae.

Head:

a common term that includes both the true head (cephalon) and the thorax area, which are below the carapace.

Heterogeneous:

different; diverse.

HIG:

heterogeneous individual growth.

H2S:

hydrogen sulphide.

Juvenile:

this is a very indefinite term and could be used to refer to any prawn that is no longer a larva but is not yet sexually mature. However, in farming, this term is usually used to refer to animals which are larger (older) than PL when used for stocking grow-out ponds (or open waters), that is prawns up to about 3 g in weight. The main text of the manual contains details of the rearing of PL to juvenile sizes in nursery facilities. In their natural habitat, freshwater prawns at this stage can move against strong currents, climb rapids, and move across wet areas to other waters. They are very hardy by this time.

Lab-lab:

a term which originated in the Philippines, that refers to the complex of blue-green algae, diatoms, bacteria and various animals that forms on the bottom or other surfaces of ponds and tanks.

Larva:

singular of larvae.

Larvae:

animals that have hatched from eggs but have not yet metamorphosed into postlarvae. They require brackishwater and swim upside down, tail up and backwards. Their anatomy (form) is also different from juveniles or adults.

Metamorphosis:

the process of transformation by which a larva becomes a postlarva and takes on the miniature appearance and the behaviour of an adult.

Moult:

to cast the shell.

Orbit:

eye socket.

Ovigerous:

having ripe ovaries.

Penaeid:

a crustacean which belongs to one of the two main groups (infraorders; sections) which form the suborder Natantia of the order Decapoda. This group is called the Penaeidea; thus these crustaceans are commonly known as penaeids. Within this infraorder (Penaeidea) the family Penaeidae contains most of the commonly farmed marine shrimp (e.g. Litopenaeus (Penaeus) vannamei, L. stylirostris, Penaeus monodon, P. semisulcatus, Fenneropenaeus merguiensis, F. chinensis, Marsupenaeus japonicus, Farfante-penaeus aztecus and Metapenaeus spp.).

Pereiopods:

an anatomical term, referring to the five pairs of legs below the thorax. The first two pairs are used for catching food, in mating, and in agonistic behaviour; the last three pairs are ‘walking legs’.

PL:

an abbreviation for postlarva, postlarvae

Planktonic:

living organisms (mainly microscopic) that are found within the body of the water (in other words, the opposite of benthic).

Pleopods:

an anatomical term, referring to the five pairs of legs below the abdomen (sometimes called the ‘tail’, when prawns are headed before sale) of the prawn, which are used mainly for swimming (swimmerets).

Pleura:

an anatomical term, referring to the sides of the abdominal segments.

Postlarva:

singular of postlarvae (PL).

Postlarvae:

a term (PL) usually applied to animals from immediately after metamorphosis from the larval stage up to about 10-20 days later. This term and the word ‘juvenile’ are applied very loosely and sometimes synonymously. Postlarval freshwater prawns swim and behave like adult prawns and, as they age, cling to or crawl on surfaces rather than swim freely in the body of the water.

ppm:

parts per million. A unit of chemical measurement used for reporting the levels of trace materials (e.g. oxygen dissolved in water) or of an additive (e.g. active chlorine). It is equivalent to 1 ml/m3 , 1 g/mt, or 1 mg/litre, for example. Where this manual prescribes the addition of a substance at a certain level, the actual amount to add can be calculated as follows. Say that you are recommended provide 50 ppm of substance X in a container (e.g. a tank). Let us suppose that the volume of water in the tank that you want to dose is 250 L. The expression 50 ppm (parts per million) means 50 parts of substance X to every 1 million parts of water (e.g. 50 ml of substance X in 1 million ml of water). As 250 L = 250 000 ml, the amount of substance X (which may be measured in ml or g) to add is: 50 x 250 000 ÷ 1 million = 12.5 ml (or g).

ppt:

parts per thousand. A unit of measurement usually applied to salinity. Also written in other documents as ‰. The salinity of full seawater varies but is often around 35 ppt (35‰). The water in freshwater prawn (Macrobrachium rosenbergii) larval rearing tanks is kept at 12 ppt (12‰).

Prophylactic:

a medicine or course of action which tends to prevent disease.

Protozoa:

a microscopic (usually single-celled) animal.

Puddling:

breaking the structure of the soil before the pond is filled. This is achieved by saturating the soil at the bottom of the pond; allowing the water to soak into the soil; and hoeing or ploughing it. The amount of water necessary to saturate the soil is roughly 200-300 mm (2 000-3 000 m3 /ha).

Rostrum:

anatomical term, referring to the sharp ‘beak’ which extends from the head of prawns.

Salinity:

see ppt.

Sequester:

bind (see chelator).

Sessile:

not on stalks (applies to larval eyes in the first larval stage).

Substrate:

something which provides extra shelter in a tank or pond, such as nylon screens or nets, pipes, branches, etc.

Supernatant:

the clear liquid after a precipitate has settled.

Swimmerets:

synonym for pleopods.

Tail:

a common term referring to the abdomen, or rear part of prawns.

Telson:

anatomical term, referring to the pointed central projection of the last abdominal segment of prawns. The telson and the uropods together form the ‘tail fan’ of prawns (and other crustacea).

Thorax:

part of the area under the carapace. Contains the segments from which eight appendages originate. See Table 1 of the main text for details.

Uropod:

anatomical term, referring to two rigid structures that appear on the final abdominal segment at the sides of the telson.

Ventral:

lower.

Walking legs:

synonym for the 3rd, 4th and 5th pereiopods.

Abbreviations

NOT ALL OF THE FOLLOWING abbreviations have been used in this manual. However, they are provided to help you when you read other documents.

<

less than

>

greater than

   

n.a.

not analysed or not available

   

µm

micron

mm

millimetre

cm

centimetre

m

metre

km

kilometre

inch

inch

ft

foot

yd

yard

mi

mile

   

ft2

square foot

yd2

square yard

mi2

square mile

   

m2

square metre

ha

hectare

km2

square kilometre

   

cc

cubic centimetre (= ml)

m3

cubic metre

   

ft3

cubic foot

yd3

cubic yard

   

µl

microlitre

ml

millilitre (= cc)

L

litre

   

µg

microgram

mg

milligram (milligramme)

g

gram (gramme)

kg

kilogram (kilogramme)

mt

metric ton (1 000 kg) [also written as tonne]

   

oz

ounce

lb

pound

cwt

hundredweight [value differs in UK (‘Imperial’) and US units - see weight

 

conversions]

t

ton [value differs in UK (‘Imperial’) and US units - see weight conversions]

   

psi

pounds per square inch

   

GPM

(‘Imperial’ = UK) gallons per minute

MGD

million (‘Imperial’ = UK) gallons per day

CFM

cubic feet per minute

   

ppt

parts per thousand (‰)

ppm

parts per million

ppb

parts per billion (thousand million)

   

min

minute

hr

hour

   

kWhr

kilowatt-hour

Conversions

THIS SECTION OF THE ANNEX should be used in conjunction with the abbreviations section. Please note that the words gallon and ton have different values depending on whether the source of the text you are reading is ‘British’ or ‘American’ in origin.

LENGTH:

1 µm

0.001 mm = 0.000001 m

1 mm

0.001 m = 1 000 µm = 0.0394 inch

1 cm

0.01 m = 10 mm = 0.394 inch

1 m

1 000 000 µm = 1 000 mm = 100 cm = 0.001 km = 39.4 inch = 3.28 ft = 1.093 yd

1 km

1 000 m = 1 093 yd= 0.621 mi

   

1 inch

25.38 mm = 2.54 cm

1 ft

12 inch = 0.305 m

1 yd

3 ft = 0.914 m

1 mi

1 760 yd = 1.609 km

WEIGHT:

1 µg

0.001 mg = 0.000001 g

1 mg

0.001 g = 1 000 µg

1 g

1 000 000 µg = 1 000 mg = 0.001 kg = 0.0353 oz

1 kg

1 000 g = 2.205 lb

1 mt

1 000 kg = 1 000 000 g = 0.9842 UK t = 1.102 US t

   

1 oz

28.349 g

1 lb

16 oz = 453.59 g

1 UK cwt

112 lb = 50.80 kg

1 US cwt

100 lb = 45.36 kg

1 UK t

20 UK cwt = 2 240 lb

1 US t

20 US cwt = 2 000 lb

1 UK t

1.016 mt = 1.12 US t

VOLUME:

1 µl

0.001 ml = 0.000001 L

1 ml

0.001 L = 1 000 µl = 1 cc

1 L

1 000 000 µl = 1 000 ml = 0.220 UK gallon = 0.264 US gallon

1 m3

1 000 L = 35.315 ft3 = 1.308 yd3 = 219.97 UK gallons = 264.16 US gallons

   

1 ft3

0.02832 m3 = 6.229 UK gallons = 28.316 L

   

1 UK gallon

4.546 L = 1.2009 US gallons

1 US gallon

3.785 L = 0.833 UK gallon

   

1 MGD

694.44 GPM = 3.157 m3 /min = 3 157 L/min

CONCENTRATION - DISSOLVING SOLIDS IN LIQUIDS:

1 %

1 g in 100 ml

1 ppt

1 g in 1 000 ml = 1 g in 1 L = 1 g/L = 0.1%

1 ppm

1 g in 1 000 000 ml = 1 g in 1 000 L = 1 mg/L = 1 µg/g

1 ppb

1 g in 1 000 000 000 ml = 1 g in 1 000 000 L = 0.001 ppm = 0.001 mg/L

CONCENTRATION - DILUTION OF LIQUIDS IN LIQUIDS:

1 %

1 ml in 100 ml

1 ppt

1 ml in 1 000 ml = 1 ml in 1 L = 1 ml/L = 0.1%

1 ppm

1 ml in 1 000 000 ml = 1 ml in 1 000 L = 1 µl/L

1 ppb

1 ml in 1 000 000 000 ml = 1 ml in 1 000 000 L = 0.001 ppm = 0.001 ml/L

AREA:

1 m2

10.764 ft2 = 1.196 yd2

1 ha

10 000 m2 = 100 ares = 2.471 acres

1 km2

100 ha = 0.386 mi2

   

1 ft2

0.0929 m2

1 yd2

9 ft2 = 0.836 m2

1 acre

4 840 yd2 = 0.405 ha

1 mi2

640 acres = 2.59 km2

TEMPERATURE

:

°F

(9 ÷ 5 x °C) + 32

°C

(°F - 32) x 5 ÷ 9

PRESSURE:

1 psi

70.307 g/cm2

Scientific units

Scientists have a different way of writing some of the units described in this glossary. They use what is called the Systčme International (SI). The units are referred to as SI units. For example: 1 ppt, which can be written as 1 g/L (see concentration above) is written as 1 g L-1 in scientific journals. 1 g/kg is written as 1 g kg-1. 12 mg/kg would be written as 12 mg kg-1. 95 µg/kg would be written as 95 µg kg-1. A stocking density of 11 kg/m3 would be written as 11 kg m-3. This system of standardisation is not normally used in commercial aquaculture hatcheries and grow-out units and has therefore not been used in this manual. More information about this topic can be found on the internet by searching for SI Units (e.g. www.ashree.org/book/siguide.htm)

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