MEREA: Equipe Méditerranéenne de Recherche Aquacole
(Mediterranean Aquaculture Research Team)
Mr. D. COVES
1. Introduction
From 1974 to 1982, large scale sea-bass rearing has permitted the production of several hundreds of thousands of fry per year in French hatcheries.
However, the rearing results were incertain, irregular and poor, with survival rates ranging between 0 and 40 % after two months.
Therefore, producers were forced to use big rearing volumes and great quantities of larvae to ensure sufficient production.
Since 1983, the PALAVAS experimental centre has perfected rearing techniques and so larval behaviour, survival and animal productions are better.
As this technique proved to be reliable at semi-intensive and intensive pilot scale it is now possible to propose technological norms and estimate production costs for this phase of sea-bass rearing.
2. Review of rearing conditions and block points with the “green water” technique:
2.1. General conditions of rearing
The feeble density lavral rearing technique known as the semi-intensive “green water” type has been described by BEDIER (1979). It is distinguished by the principal parameters here following :
Initially low concentration in rearing with about 20 larvae per liter in a black tank of 10 m3.
The rearing environment is stagnant with the phyto-planktonic bloom for the first 20 days. The water renewal is carried out progressively little by little.
The artificial rearing, with which mercury or fluorescent lighting is employed gives intensities of 2000 to 5000 lux at the surface of the tanks when the hatching starts.
2.2. Anomalies encountered
Two principal anomalies occur frequently at this point :
An anomalie in behaviour is remarked from the 20th to 30th day in rearing (temperatures of 18 to 20° C.). It is distinguished by fits of giddiness together with loss of appetite and the production of white faeces. In some cases these symptomes are followed by the death of whole stock.
Anatomical anomalies.
On one hand, some rearings present a high percentage of individuals having a malformation of the mandibular arch (prognathic, bilateral or simple operculata); on the other hand, skeletal lordosis type malformation appears in 80 to 90 % of the animals when they reach 20 cm in lenght (CHATAIN in process) so many weak fish, greatly reduce rearing performances and survival rates at weaning stage are very average (CHATAIN in process).
In this last case there is a correlation between the presence of a lordosis and the absence of a functional gassy bladder (CHATAIN in process)
3. Solutions to block points
3.1. A pragmatic approach
From 1984 onwards, the overall improvement of the quality of the rearing environment has been elaborated. A pragmatic approach was first employee and this technique let to the reproduction of larvae in natural living conditions (COVES in process, COULET, 1985)
In consequences, the “green water” was abolished and in place there is a continuous water renewal from the beginning of rearing. The artificial light (neon) was replaced by a natural light of more feeble intensity (maximum 1000 to 1500 lux from November to March) and so discontinuous (9 to 12 hour per day) during the rearing season.
On the principle of this method, two rearing techniques are employed simultaneously. one of these techniques known as the intensive, is carried out in tanks of 2 m3 with great quantities of larvae at the beginning (50 – 100 larvae per liter) the other technique known as the semi-intensive, in tanks of 10 m3 with small quantities of larvae (10 – 25 larvae per liter) (tab. no 1, page 6)
The results obtained at pilot scale for both techniques are very significant right away.
The fits of giddiness stop completely and mandibular and opercular anomalies disappear.
Survival rate progress from 15 % to 40–50 % on average (fig. no 1, 2, 3, 4 and tab, no 2 page 7, 8, 9, 10, 11).
THe results obtained on all the tests show that this method is reliable when the purely technological problems are under control (pumping, heating).
The average percentage of animals having a functional air bladder is greater but results very a lot still. (fig. no 1 and page 7 and 9, tab, no 2 page 11).
3.2. Experimental approach:
On parallel with the pragmatic attempts carried out at pilot scale, many tests have been tried out at experimental level in small pay load cylinderconical units of 500 liters.
In 1985, the results described here following have been transferred to intensive pilot scale so a new and extremely reliable rearing technique could be started.
3.2.1. Influence of colour of the tanks
The comparaison is carried out between white walled and black walled tanks.
The results obtained are clear. Walls painted in black encourage better behaviour, predation, growth and survival (RONZANI in process).
3.2.2. Influence of the incident parameter
The different tests carried out in black walled tanks having incandescent artificial lighting showed the important part played by the light parameter on the quality of rearing.
a) The photoperiod
Constant lighting handicaps the inflation of the gassy bladder and doesn't permit good consumption of the prey during the interval which corresponds to the natural night period ( RONZANI in completion).
b) Light intensity
During a first experiment the 70 lux-1 800 lux scale was tested for the first 40 days of rearing. The intensity tested was constant for 9 hours out of 24 hours. Only the 1 800 lux doublet shows abnormality in behaviour and giddiness from the 20th to the 30th day (WEPPES, JOASSARD in process).
During a second series of experiments, the 50 – 5000 lux scale was tested during the first 20 days of rearing. The correlation was found between the light intensity and the rate of the gassy bladder inflation (JOASSARD in progress).
3.2.3. Influence of the environment and the feed sequence
Recent experiments have permitted to define a new method of rearing by controlling the environment and the feed sequence, during the first fortnight of rearing. This technique finally gives the possibility of obtaining good rates of the gassy bladder inflation from the 12th day onwards, ensuring a good quality fingerling production without malformation.
Tested at intensive pilot scale, this method gave reliable results from a quantity point of view (survival between 35 and 55 %) and a quantity point of view (normal fingerling rates 75 and 95 %) (fig. no 3, page 9).
4. Technico-economical norms
The numerous tests at experimental level and the reliability of the results obtained when transferred to pilot level have permitted the estimation of the technico-economical norms. These are all the more realistic as these calculations concern the rearing of about 1 million larvae of 45 to 50 days of age produced in 12 tanks of 2 m3 each, carried out in 3 cycles during the 1985 season (fig. no 4, page 10).
These norms form a tool of efficient programmation more than economic balance of a production technique would. These figures show clearly that the cost of production, not counting the depreciation of a 45 – 50 day old larvae is relatively low, 0, 12 FF; and that only a drop in the cost feed (which is 90 % per price of cysts) could permit a real reduction in the cost of this phase of sea-bass rearing (tab. no 3, page 12 – 13).
5. Conclusion
Two years of zootechnical research work has permitted to raise the important block points which has hindered sea-bass rearing. This break through now permits every potential producer, to organize clearly the management of his enterprise. The next step to be taken is the productivity returns which will stay relatively low as long as Artemia is not replaced by artificial feed.
Adress: Chemin de Maguelone
34 250 - PALAVAS LES FLOTS
FRANCE
| Table No 1 : | REARING METHOD, 1984 |
| INTENSIVE | SEMI - INTENSIVE | ||||
| TANK | - volume (m3) | 2 | 10–15 | ||
| - shape | cylindro-conical | circular | |||
| - colour | black (white bottom) | black | |||
| ONE DAY OLD LARVAE PER LITER | 50 – 100 | 10 – 25 | |||
| LIGHTING (natural) | - period (h) | 9 – 12 | |||
| - maximal intensity (lux) | 1000 – 1500 | ||||
| WATER | - quality | opened circulating system | |||
| - renewing rate (% total volume. h.-1) | 5 (D1) | 30 – 50 (D45) | |||
| - temperature (° C) | 14 (D1) | 18 – 22 (D45) | |||
| AERATION | (liter. mn-1.m3) | 0.4 (D1) | 3.0 (D45) | ||
| PREYS | - Brachionus plicatllis (led on yeast and algae) | D 6 | – | D12 | |
| - Artemia nauplii (Sun Fransisco) | D 9 | – | D 20 | ||
| - Artemia metanauplii (led on dry compounded powder) | D 16 | – | D 45 | ||
Figure No 1: - Low density sea-bass larval rearing, Dicentrarchus Labrax
Evolution of survival and of normal air bladders rates after the first 50 days during the 1976 – 1984 period.
Figure No 2: - Low density sea-bass larval rearing, Dicentrarchus labrax
Evolution of yulds and productions obtained after the first 50 days during the 1976 – 1984 period.
Figure No 3: High density sea-bass rearing, Dicentrarchus labrax
Evolution of survival and normal air bladders rates after the first 50 days during the 1981–1985 period.
* Result of the first cycle 1985
** Result of the second 1985
*** Result of the third cycle 1985
Figure No 4: High density sea-bass larval rearing, Dicentrarchus labrax
Evolution of yulds and productions obtained after the first fifty days during the 1981–1985 period.
| Table No 2 : | AVERAGE PILOT PRODUCTION RESULTS, 1984 |
| M E T H O D | rearing quality | total survival rate D 45 (%) | swimbladder inflation rate D45 (%) | total fry number per m3 D45 | total normal fry number per m3 D45 |
| SEMI - | 1 | 57.0 | 48.5 | 10270 | 4980 |
| INTENSIVE | 2 | 57.0 | 48.5 | 10270 | 4980 |
| INTENSIVE | 1 | 27.5 | 28.0 | 21100 | 5890 |
| 2 | 44.5 | 23.0 | 44300 | 10080 |
* with an inflated swimbladder
1 means obtained from attempts
2 means obtained from attempts realised without any trouble
| Table No 3 : | SEA-BASS LARVAE REARING TECHNICO ECONOMIC RESULTS, 1984 |
| INTENSIVE | SEMI-INTENSIVE | ||||||||||||
| REARING METHOD AND RESULTS SUMMARY | |||||||||||||
| * TANKS VOLUME (M3) | 2 | 10 | |||||||||||
| * DI LARVAE A LITER | 100 | 18 | |||||||||||
| * SURVIVAL RATE (%) | 44 | 57 | |||||||||||
| * TEMPERATURE (°C) | 18 | 18 | |||||||||||
| * RENEWING RATE(%) | 5 | → | 50 | 3 | → | 30 | |||||||
| * AERATION (L.MN-1M-3) | 0.4 | → | 3.0 | 0.4 | → | 3.0 | |||||||
| * PREYS | ROTIFERS | ► | ARTEMIA | ROTIFERS | ► | ARTEMIA | |||||||
| 10000 D45–50 LARVAE PRODUCTION COST | COST (FF) | % | % | COST (FF) | |||||||||
| D1 LARVAE | 39.1 | 2.4 | 1.9 | 30.9 | |||||||||
| * | Rotifers | 19.6 | ] | [ | 174.1 | ||||||||
| PREYS | * | Nauplii | 25.0 | 56.3 | 77.8 | 3.7 | |||||||
| * | Metanauplli | 866.0 | 1069.8 | ||||||||||
| * | Heated water | 28.6 | ] | [ | 66.7 | ||||||||
| FLUIDS | * | Normal water | 0.9 | 1.9 | 4.3 | 1.8 | |||||||
| * | Air | 0.1 | 0.3 | ||||||||||
| * | General | 205.0 | ] | [ | 198.0 | ||||||||
| LABOUR | 39.5 | 16.0 | |||||||||||
| * | Counting | 435.0 | 57.3 | ||||||||||
| * TOTAL PRODUCTION COST | 1620 | 1603 | |||||||||||
Table No 4 : Technico-economical norms of intensive sea-base larval rearing 1985
| 1. | TECHNOLOGY and RESULTS | |||||||||||||||||||||||||||||||||||||||
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| 2. | PRODUCTION COSTS | |||||||||||||||||||||||||||||||||||||||
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BIBLIOGRAPHY
BEDIER, E., 1979 - Production à l'échelle pilote d'alevins de loup (Dicentrarchus labrax L.). symposium on the early life - History of fish - Woodshole, USA, 2 – 5 April 1979.
COULET, J.L., 1985 - Synthèse des données acquises sur l'élevage larvaire du loup (Dicentrarchus labrax). Techniques semi-intensive et intensive. Rapport interne IFREMER, équipe MEREA - 27 pages.
