Oxygen requirement of fish ranges from 100–1100 mg/kg/hours. Oxygen consumption is not a standard value. It depends largely on fish species, size of fish, physiological condition of individual and on several environmental factors.
In general, oxygen consumption
With the increase or decrease of 10°C water temperature oxygen consumption duplicates or decreases to 50 percent. It is relatively higher (calculated on 1 kg body weight) in smaller individuals than the bigger ones. Oxygen consumption of starving fish is lower. After taking food it increases sharply. Later it decreases, but 2–3 days are necessary to get to the previous level.
Though there are differences between fish species (for example oxygen requirement of rohu and silver carp is higher than that of mirror carp), average oxygen requirement, which must be satisfied during transportation of nursed fry and fingerlings at 22–25°C and at 30°C is shown in Table 18. Table 19 presents oxygen consumption of broodfish.
TABLE 18
OXYGEN CONSUMPTION OF CARP FRY AND FINGERLING
AT DIFFERENT WATER TEMPERATURE
| Weight of fish (g) | Oxygen consumption (mg/kg/hour) | |
| 22–25°C | 30°C | |
| 0.3 | 1230 | 2100 |
| 0.4 | 1180 | 2000 |
| 0.5 | 1150 | 1900 |
| 1.0 | 1000 | 1700 |
| 2.0 | 900 | 1500 |
| 3.0 | 830 | 1400 |
| 5.0 | 740 | 1250 |
| 10.0 | 660 | 1100 |
| 20.0 | 550 | 950 |
| 30.0 | 530 | 900 |
| 40.0 | 520 | 880 |
| 50.0 | 500 | 850 |
TABLE 19
OXYGEN CONSUMPTION OF BROODFISH
| Body weight (kg) | Oxygen consumption (g/hour) | |
| 22–25°C | 30°C | |
| 1 | 0.3 | 0.6 |
| 2 | 0.5 | 1.2 |
| 3 | 0.7 | 1.4 |
| 4 | 0.9 | 1.8 |
| 6 | 1.3 | 2.5 |
| 8 | 1.6 | 3.2 |
| 10 | 1.9 | 3.8 |
(“Conditioning”)
As mentioned earlier, fish with empty intestine consume less oxygen than full fish. Moreover, faces, urea and ammonia produced during digestion deteriorate water used for transport. So, intestine of fish should be discouraged and fish should be accustomed to strong stress before transport. For that fish are kept in special ponds (“pakai pond”), in enclosures prepared in bigger pond, or in hapas before transportation where they are prepared to transportation.
Conditioning of fry requires 3–4 days in so called “pakai pond”. Day before transfer of fry to this pond fish are fed with well soaked mustard oil cake. Fish are caught by net on the following morning and they are kept in the net for half an hour in overcrowded condition. In the meantime water is violently jerked in the net. Later fish are transferred to pakai pond and stocked at the rate of 2 lac/bigha. After this, during the next two days nursed fish are fed daily with soaked mustard oil cake (daily ration is 40–50 kg/bigha) and before feeding they are caught and kept in net for half on hour. Water in net is strongly splashed between the fish. Fish on third day, are kept in the net about one hour with strong splashing of water. After that those fish which run against the artificially created water current are selected for transportation.
If this process is carried out in hapas (made from mosquito net), stocking density in hapa is 2–3000 nursed fry or small fingerling/ m3 water. Duration of conditioning is 10–16 hours. Splashing of water is done frequently during this period. Sorting, counting and packing are carried out from conditioning hapa.
No special conditioning of feeding fry is required before transportation.
For fish transport different sizes of plastic bags, or containers of different size and shape, manufactured from PVC, fiberglass, iron, or aluminium are used.
Fish are frequently injured during conditioning and transportation. Antibiotics may be used at the rate of 20–40 mg/litre for avoiding infection if transportation time is long. Use of 0.05–0.3% kitchen salt during transportation decreases activity and stress-sensibility of fish.
Overloading of transport facilities must be avoid. After transportation, gradual equalization of temperature and water quality is essential during release of the fish.
This is one of the most widespread method for egg, fry and fingerling transportation. Sometimes plastic bags are used also for broodfish transportation. For eggs and newly hatched fry bags of 0.04 mm thickness, and for fingerling bags of 0.06–0.08 mm thickness are recommended. For transportation of fish bigger than fingerling, plastic bags of 0.1–0.15 mm thickness are preferred. Double (or for broodfish, triple) wall bags are recommended for increasing security of transport.
The simplest way is to prepare plastic bags using a plastic hose. It should be purchased in different width and cut on required length. Volume of plastic bags prepared from plastic hose of different width and cut on different size, moreover weight of oxygen can be filled and weight of oxygen utilizable are shown in Table 20. (At the calculation of oxygen quantity, it should be considered that 1/3 of total volume of plastic bag is filled up with water and 2/3 with oxygen. 60 percent of oxygen is considered as utilizable. 1 liter oxygen is 1.43 g.)
To avoid sharp increasing of water temperature in plastic bags some ice (packed in small plastic bag, and placed in the transportation bag) can be used. For an average size plastic bag 200–500 ml of water should be freezed. It is strictly forbidden to use more ice, because sharp and significant changing of water temperature may be harmful. Plastic bags should be transported in shade.
When eyes start to develop it is the best time for egg transportation. If embryo is less developed, splashing of water can cause some injuries with tearing down of cells from embryo. Later, resistance of egg shell is lower against mechanical impacts. At 27–28°C water temperature about 10 g oxygen is necessary for 2–4 hours transportation of 100–200 thousand eggs.
For a very long transportation (2–3 day) larvae should be packed soon after hatching. Newly hatched fry can survive such a period without difficulties, consuming their own yolk. Quantity of oxygen necessary for 3 days transport of 5–10 000 fry is 10 g.
Numbers of feeding larvae transported in plastic bags by Bangladeshi fish culturist are: For long distance transportation (for 7–8 hours) 125 g feeding fry (about 50 000) are packed in standard bag of 80–90 × 40–50 cm. For short transportation, loading is about 200 g (80–90 000). Loading of plastic bags for silver carp and catla is less, about 80% of the above mentioned values.
TABLE 20
UTILIZABLE OXYGEN IN PLASTIC BAGS OF DIFFERENT SIZES
| Width of plastic hose cm | 40 cm | 50 cm | 60 cm | 70 cm | 80 cm | ||||||||||
| Total volume | Oxygen | Utilisable oxygen | Total volume | Oxygen | Utilisable oxygen | Total volume | Oxygen | Utilisable oxygen | Total volume | Oxygen | Utilisable oxygen | Total volume | Oxygen | Utilisable oxygen | |
| liter | g | g | liter | g | g | liter | g | g | liter | g | g | liter | g | g | |
| 30 | 12 | 10 | 6 | 16 | 14 | 8 | 19 | 17 | 10 | 22 | 20 | 12 | 25 | 20 | 12 |
| 40 | 21 | 20 | 12 | 27 | 25 | 16 | 32 | 30 | 18 | 37 | 30 | 18 | 42 | 40 | 24 |
| 50 | 32 | 30 | 12 | 40 | 35 | 21 | 48 | 45 | 27 | 56 | 50 | 30 | 64 | 36 | |
| 60 | 45 | 40 | 34 | 57 | 50 | 30 | 68 | 60 | 35 | 79 | 70 | 42 | 90 | 80 | 48 |
| 70 | 60 | 50 | 30 | 76 | 70 | 42 | 90 | 80 | 48 | 106 | 100 | 60 | 122 | 110 | 60 |
Duration of transportation, optimal loading of different size plastic bags by nursed fry and fingerling and broodfish should be calculated by the data of Table 18, 19 and 20.
It is better to avoid long transportation of broodfish in ripe condition (before reproduction). If long distance transportation of broodfish is necessary in ripe condition, plastic bags should be used. To avoid perforation of bags, first ray of fins must be wrapped or a plastic tube with appropriate diameter should be drawn on them.
Hundi with 20–40 liter of volume is used traditionally for fish seed transportation. Earlier, hundi was made by clay, at present aluminium hundies are used. Clay hundies had a special advantage: evaporation trough the wall of hundi kept cool the water in pot. Aluminium hundi has no such advantage. Optimal loading of hundi is shown in Table 21.
TABLE 21
COMMON MEANS OF LIVE FISH/FISH SEED TRANSPORT
IN RURAL AREAS (KUMAR 1990)
| Live materila | Container | Approx. Water volume (L) | Quantity (Nos) | Safe limit (Hours) | Remarks |
| Spawn | Aluminium containers (Hundies) | 30 | 50000–75000 | 8–12 | About 100g of red soil is added to each hundy. Method prevalent in bundh breeding areas. Sarker - personal communication. |
| Early fry (12-15mm) | -do- | 30 | 4000–5000 | 8–12 | Frequent water change every 2–3 hours and container gentle splashing |
| Fry (50 mm) | -do- | 20 | 250–350 | 6–7 | With change of water every 2–3 hours. Mortality rate about 1–57 |
| Fry (20–30 mm) | -do- | 20 | 500–600 | 6–7 | With change of eater every 2–3 hours. Mortality rate about 1–57. |
| Fingerlings (100–150 mm) | -do- | 20 | 75–100 | 4–6 | With change of water in every 2 hours. Mortality at the rate of 1–5%. Maximum incidence of mortality occurs in the case of rohu. |
| Brood fish | -do- | 20 | 5–6 kg | 1 | Farmers generally mix the country liquor at the rate of 1 drop/1. |
| Brood fish | -do- | 30 | 10–12 kg | .5 | For short distance transport Sarkar-personnel communication |
Iron barrels with about 200 liter capacity are also used for fish transportation. Usually 10–12 000 nursed fry of 1 inch size, or 8–10 000 2.0–2.5 inch size fingerlings (12–14 kg and 15–20 kg respectively) are stocked in one barrel for 1–2 days transportation. One track (7 ton capacity) can carry about 20 barrels (2 laks of fry). Barrels are covered by jute bag. Well water or pond water of good quality is used for filling up the barrels. During transportation frequent changing of water is necessary in each consecutive 2–3 hours. At least ⅔ of water must be removed and replenished. In addition to this, continuous hand-agitation of water is necessary. By using aerators or oxygen instead of hand-agitation double loading of barrels is possible. Moreover, no water exchange is required if duration of fish transportation is less than 6 hours.
Different sizes of fiberglass or canvas tanks, or tanks made from galvanized iron sheet are also used for fish transport. Double wall insulated tanks are the best for long transportation. Loading capacity of this tanks is about 100–130 kg/m3 for few hours transport. Using oxygenation or aeration loading should be increased to 60–80%.
Petrol-resistant PVC pipes with dia of 0.7–1.5 cm are suitable for preparation of aerators. Tube should be fixed on an iron frame. Shape of the frame should be made according to shape of the transport tank. Piercing must be done using sewing needle, 4–7 mm from each other on upper side of the PVC pipe. For perforation of the aerator pipe needle used must be with diameter as small as possible. Efficiency of aerator producing big size oxygen or air bubble is low. Perforation should be of same diameter, so needle should be stick in equally to avoid differences. Aerator tube should be connected to oxygen cylinder or compressor with the same PVC pipe (Figure 12).
If aeration carried out on oxygen cylinder, using of pressure-regulator is essential. For proper aeration a fish transport tank of water volume of 1 m3 about 2 m of perforated PVC pipe is necessary. A small size oxygen cylinder, contains 1.36 m3 oxygen, can supply it for about 4 hours. Using big size cylinders (which contains about 10 m3 oxygen) three tanks of this size can be supplied for 8–10 hours.
Figure 12
Different aerators suitable for oxygen supply of fish transport tanks
(Modified after Woynarovich and Horvath, 1980)
