The papers submitted for the technical sessions (see Annex C) will be screened by an editorial committee and those selected as suitable for publication will be issued in the series Studies and Reviews of the GFCM.
No papers were presented for this group. However, the discussion centred on the culture of a cephalopod Sepia officinalis both in Italy and Spain.
In addition to what had already been reported in the Spanish national report, Mr. Pascual described their feeding techniques. In the first two months of life the main prey are Mysidacea, and from the third month - when they reach 7 cm in length - they are switched to live fish.
Mr. Breber said that in Lesina (Italy) for the initial stages, S. officinalis is fed on amphipods, which are later on supplemented by fish of the genus Aphanius and Atherina.
Questions from the audience were on the convenience of culturing such a carnivore that will compete, at least partially, with gilthead sea bream for small crustaceans in extensive culture, and on the cannibalistic behaviour of the very aggressive young males (6–7 cm in length) that would limit their interest for intensive culture. It was pointed out by Mr. Pascual that this species may be competitive for special markets as the Spanish one in view of the good price brought by the very young cuttlefish of 6–7 cm (around Pts. 350–400/kg) and the extremely fast growth rate (from 0.1 g in March to 400 g in October) that make the culture of the very young ones economically interesting.
Three papers were submitted on crustacean culture. Of the local penaeid species, Penaeus kerathurus has been retained by the majority of the laboratories and among the exotic species, P. japonicus has been tried on an experimental level by some laboratories. It can be said that the situation of the region, as far as penaeid culture is concerned, is still at the laboratory or pilot plant stage. Financial considerations do not make it still attractive for large investment needed for commercial operations, and the research groups are still refining their methods in order to obtain lower production costs and better efficiency in the overall operation.
In the first paper the French group of the Station d'aquaculture DEVA SUD working at the pilot plant stage reported on a modular technique of larval culture at high densities. In the intersessional period a technique for induced maturation has been perfected, so that now the station does not have to rely on gravid females collected from the wild. For feeding the breeders, mussel and crustacean ground meat is used in fresh form, and for the larval stages a mixture of algae of the genus Monochrysis, Tetraselmis and Cylindrotheca is given, supplemented by yeast. For the carnivorous stages, artemia nauplii are employed, sometimes given as decapsulated non-hatched cysts. For growth of juveniles to adult size pellets are given, with a conversion rate of 2.3:1.
The group reported a new technique developed by the COB (Centre océanologique de Bretagne) for larval rearing, consisting in a finely ground mussel meat, mixed with powdered algin, which is sprayed at high pressure (using a paint sprayer) on the larval tanks. The algin acts as binding material avoiding the leaching of nutrients in the water.
Dr. de Pauw pointed out that the use in several laboratories of Tetraselmis and Skeletonema was based only on repetition of techniques developed some years ago and mentioned that Nannochloris species were easier to maintain than Tetraselmis and Skeletonema. The Spanish laboratory of Cadiz (IIP) reported in the discussion which followed on the feedstuff used for penaeid culture that for larval rearing they used the alga Nannochloris oculata and rotifers, but a certain toxicity was observed at high densities. The use of Tetraselmis allowed densities of 350 rotifers/cc.
At this point the question was raised of digestibility of the various species of the Chlorococcales, and the need for further taxonomical studies since the diversity of pigments encountered suggest that the taxonomical groupings are probably wrong.
In the second paper Mr. Kloudatos from Greece reported on their experiments on rearing P. kerathurus. For larval rearing, tanks with the double bottom system were used and for the carnivorous stages artemia nauplii plus clam and mussel meat were given. For outdoor operations fresh or frozen crab and clam meat were used, but a clear preference for crab meat was shown. It was mentioned that large quantities of mussels and crabs were available at relatively low cost.
Crab meat was also used as a feedstuff by the laboratory of Santander (IOE), Spein, as a replacement for artemia. In this case a more frequent change of water, than with the use of artemia, is required to maintain an adequate water quality.
The third paper on shrimp culture, from Italy, reported on experiments to grow shrimp in thermal effluents. In this case juvenile shrimp were used in the experiments and were fed trash fish (anchovies) and mussel meat.
The discussion that took place during the shrimp session pointed out quite clearly several problems. Artemia availability remains a serious problem as many laboratories still rely on cyst imported from the U.S.A. Also, the nutritional requirements of the species cultured, and especially in the case of P. kerathurus, are not fully understood and will require more detailed research than that actually conducted on qualitative and quantitative requirements. From the discussions on the live food cultures, some concern was also expressed regarding the biochemical composition of the algal species used and their influence on the resulting nutritional value of the rotifers feeding on them.
For broodstock preparation, the progressive decrease in fecundity observed in P. japonicus suggests that nutritional requirements for ovarian development and maturation are not fully met, pointing out another area for further research (see Recommendations COPRAQ/79/3–4).
Eight papers were presented on finfish culture, pointing out that there is generally more interest in the region for fish culture research than for crustaceans or mollusc.
Although, according to the agenda, the discussion had to centre on results of research on nutrition, there was considerable interest in disease aspects, which gave rise to a lively discussion on the topic. For this report, we shall concentrate on nutritional aspects, mentioned during the discussions by species, and afterwards an account will be given on the disease problems discussed, in some cases related with nutrition.
The first species discussed was eel, Anguilla anguilla. It was reported by Dr. Bilio that his group in Italy was investigating the minimum protein levels for pond rearing to commercial size. The commercial feed available contains 65 percent protein, derived mostly from fish meal. Experiments were being conducted including feather meal and vegetable meal in the diet in order to avoid excessive use of fish meal. However, up to the present time, no detailed analysis on aminoacid requirements has been carried out. From their experiments, it was found that the level of carbohydrates in the diet is critical, and chitin addition was also found to improve the convertibility of the diets.
Studies conducted on fatty acids did not show grossly evident differences. What was indeed evident was the importance of considering the species behaviour related to feeding, since part of the individuals refuse to take the feed, and this can therefore lead to misinterpretation of data on average conversion rates for the diets tested. Regarding digestibility of the different components of the diets, it was reported that studies had been conducted in the Federal Republic of Germany.
An experiment on two types of cages for growing eels in the open sea was presented by Mr. Bussani, Italy. In his work, once the cages were covered by fouling organisms, such as Ulva sp., no additional food was given and the growth was reported to be satisfactory.
Sea bass, Dicentrarchus labrax, seems to be the species which is attracting more attention in the Mediterranean and also the only brackish water species whose culture from egg to marketable size is reaching the commercial stage.
In Yugoslavia, as reported by Mr. Filic, experiments on cage culture are being conducted in Limsky Kanal. As this is a protected area with some existing mussel culture, collectors are being kept near the cages to utilize the increased primary production resulting from fertilization of the water by fish faeces and unutilized feed. In this experiment trout feed is used, and the sea bass are fed twice a day until satiation, which is reached when an amount equivalent to 3–5 percent body weight is given. It was reported that food consumption in winter was the same as in summer but slower growth was also recorded. Stocking densities for 8 m3 cages were 5 kg/m3.
Opercular deformation as well as fatty livers and reduced growth were noticed in some fish reportedly correlated with low dissolved oxygen values.
For hatchery work the following feeding schedule was mentioned: the initial food organisms are rotifers, Brachionus plicatilis and mussel trocophorae, which are offered 4–5 days after hatching. Five to seven days later, the larvas are passed to artemia nauplii to be changed after 2–3 weeks to copepods. Frosen copepods are given for a period, together with artemia to ensure a smooth passage to the new diet.
The experience in France with nutrition of this species has led to the use of granulated feeds that give conversion rates around 2:1 with a cost of F.F. 4/kg of pellets. This level is considered adequate for pilot-scale production in raceways where anyway the feed cost will account for slightly over 50 percent of the production cost per kg.
From past experience, as reported by Mr. Cognie, continuous feeding is not advisable since the resulting variability in size is higher than with fractional feeding. The time required to reach the minimum market size - 200 g - using the available knowledge but without heating the water during the winter period is two summers. By the third summer the fish will reach an average size of 350 g (range 280–600 g).
Sparus aurata, gilthead sea bream, is another species that has received considerable attention from researchers on aquaculture. It may command better prices than sea bass in some of the Mediterranean countries, but up to now the development of suitable techniques for larval rearing has not progressed at the same pace as for sea bass. Survival rates are still very low (3–5 percent in the best cases) and the number of fry produced in most hatcheries is rather low, thus favouring the choice of sea bass by fry and fingerling producers.
One exception is Israel, where all efforts have been focused on sea bream, and where a multi-disciplinary approach is used in research on this species by the Hebrew University of Jerusalem and the IOLR Mariculture Laboratory at Elat.
As reported by Mr. Porter on their experiments on cage culture, specially formulated diets, with 52.5 percent protein content, using locally available ingredients, gave results comparable to a trout pollet of 40 percent protein content, so that growth experiments continue at present to use this trout pellet. Initial results showed rather bad conversion rates, in the order of 5–6:1, that were due to loss of food through the cages. This has been improved by using floating feeding trays (bringing it to values ranging from 2.5–5:1), which also provide shelter for the small fish. The final production in these cage culture experiments was high, in the order of 60 kg/m3.
Experiments of food rations were performed, and a medium-high ration of 3.8 percent body weight gave results in growth very similar to those obtained using a satiation ration of 4.8 percent body weight, and brought also better conversion rates (3.7 compared to 5.1:1 for the satiation ration).
Different stocking densities were also tested and it was found that up to 240 fish/m3 there was no inhibition in growth. Best results were reported at 180/m3 reaching 300 g average in 15 months from hatching. Actual work is centred in quantifying the nutritional requirements on vitamins and fatty acids.
Regarding feeding time, it was mentioned by Dr. Carrillo that in the research conducted in Torre de la Sal changes in the levels of aminoacids in plasma during the day were noticed; this must therefore be related with the feeding schedule and taken into consideration for future research on nutritional requirements.
As far as acceptance of dry feeds is concerned, S. aurata, together with Diplodus sargus, are superior to D. labrax as they eat crumbles more eagerly than sea bass in their larval stages; however, they show a preference for live food or frozen zooplankton.
A relatively new species, whose potential for aquaculture is being investigated, is D. sargus. Mr. Divanach reported on the results obtained in Sète, France, on the nutritional aspects. The larvae obtained with dry fertilization methods (in reduced amounts since the survival rate is in the range of 3–5 percent) are offered copepods and artemia and after three months are reared on pelleted food. Frozen wild zooplankton has been used in the initial stages and was accepted by the larvae, although after four hours in the water it no longer attracted the fish. Some work on food preferences was carried out and Daphnia sp. ranked as their preferred food organism, the least preferred foodstuff being pellets.
Regarding the behaviour of juveniles and captured adults in captivity, it was found that they adapt very quickly, resuming feeding only one hour after capture. They keep the tanks very clean, eating even their own faeces.
As an example of the continuous search for new live food organisms for larval and juvenile stages, Dr. Kahan reported on the trials being carried out in his laboratory in Israel to test the suitability of free-living nematodes of the genus Panagrellus as foodstuf.
One of the main objections that had been raised against nematodes use in the past was their apparent indigestibility. According to Dr. Kahan this is not true for all genus of nematodes, and young sea bream and mullets, as well as common and silver carp, were found able to digest Panagrellus.
Some advantages of nematodes are the possibility of culturing them at very high densities; their aminoacid composition, which is similar to that of artemia, and the possibility of using them as additives to dry pellets.
Apart from the fish species discussed, in some of the participating countries there is considerable interest for cage culture of salmon in the sea. The discussion on diseases started precisely with a paper on diseases found in salmon in Spain. Mr. Martinez Millan from ACUIGRUP reported on infections by Vibrio sp., which were isolated from the kidney, and which are associated with temperatures above 14°C. Corynebacterium is also found, but in fresh water and, according to their experience, is sometimes associated with osmotic failure. The preferred methods for treatment of these diseases are the incorporation of druge and antibiotics in the diets. Sulphamerazine, furasolidone and oxytetracycline are the more effective.
For purely marine or brackishwater species, Dr. Paperna gave an account of the problems which were found in his laboratory at Elat, Israel, and on the investigation in progress. In a study conducted on the brackishwater species, more than forty different diseases or parasites were identified for each species; however, in the work with sea bream there are three main problems for which no definitive cure has yet been identified. These diseases are infestation by Oodinium sp., systemic granulomatosis and epitheliocystis. Although in principle it was thought that these diseases could be endemic for Elat, it was soon found that the diseases were present in other hatcheries in France, converting the problem into one of general interest.
Regarding parasites, it was pointed out that with breeders or wild fry in cases up to 30–40 different parasites can be introduced in the culture systems, and are potentially more problematic in thermal aquaculture.
Epitheliocystis is caused by bacteria-like organisms, it affects mainly mullets and sea bream, and no particular cure has been found so far. It can be present also in hatcheries where it causes severe mortalities amongst the fry. However, the few survivors seem to be immune.
A point that was also emphasised is the very important role that stress plays in the onset of diseases in these species of fish. This is particularly true for the vibriosis, which can result from excess of handling, loss of scales, etc. A combined treatment of antibiotics, mainly chloramphenicol and baths of nitrofurazone, are effective.
Fatty livers in cultured fish were reported from more than one institution. It is believed to be caused by physiological stress due to an unbalanced protein ratio and is more acute in sea bass although it has been also found in sea bream.
Another disease which seems to be linked with nutrition is systemic granulomatosis, investigated by Dr. Paperna. Accumulation of tyrosine crystals in renal tubules and the urinary canal is the first stage, and can develop into chronic inflammation of the viscera and also produce progressive blindness. It was suggested that the disease could be associated with toxins present in the fish meal employed in the pellets, since changes in the diets in the early phases of the disease sometimes bring considerable improvement.
Cranial and skeletal deformations in hatchery-produced fry were reported for sea bass and sea bream. Several hypotheses were advanced on the origin of the deformation: genetic, due to egg incubation or handling or to stress or vitamin deficiency. In sea bass these deformations are sometimes associated with deformation of the swimbladder which does not fill correctly.
The discussion on the possible ways to treat the diseases mentioned especially in the case of cage culture was very lively, but no agreement was reached on either preferable products or techniques for application.
Compared with the discussions of the previous meetings of COPRAQ, there was less interest in research on mullets. This can be partly explained by the fact that many institutions of Arab countries did not attend the meeting, and also because in countries like Israel these fish are mainly cultured in freshwater environments.
