Norway's Herring Oil & Meal Industry Research Institute (SSF) has developed a new diet which it claims can wean fish larvae that were previously restricted due to lack of proper feed.
SSF produces several of the ingredients and has recently invested more than £1 million (US$1.5 million) to scale-up production.
Successful trials have been carried out at research institutes and fish farms in Europe and Asia, on species such as sole, whitefish, milkfish, halibut, herring and cod.
"The feed gives high survival," says SSF. "Growth performances are close to that of live feed when weaning is performed at early stages, and better at late weaning period. It may thus open the possibility to farm new marine fish species.
"A proper weaning diet may also limit the problems experienced by fluctuations in Artemia availability and quality."
The new diet is processed using a new concept in ingredients and process. It is microbound, and the binder holding the ingredients together in the small feed particles is a specially designed marine type.
Processed by agglomeration, the feed is based on marine ingredients with special nutritional quality and composition. "The consistency of the particles is soft," SSF explains, "and together with the fact that they are round spheres without sharp edges, the feed is easily handled by the small larvae. The feed contains a high dietary protein level - more than 60% - and a low carbohydrate content, which ensures good nutritional status for the small larvae."
In southern Europe, some farms have diversified by setting up sole broodstocks - there are already several hundred thousands of sole juveniles. Consistently high prices and demand have made sole one of Europe's most attractive aquaculture candidates.
But, despite much progress in developing experimental intensive culture techniques, there has been only limited success commercially.
"The main reason has been the absence of commercial feeds that produce high weaning survival and rapid growth to market size," says SSF. "The sole's highly developed olfactory system has tended to focus much of the research on improving palatability through chemical attractants.
More recently, research on diet digestibility in sole has demonstrated the importance of incorporating fish hydrolysates in the weaning diet.
But including these unconventional, small diameter diets presents problems of particle stability and water pollution due to excessive leaching of soluble proteins, peptides, amino acids and other highly water soluble components.
Experiments performed by Drs Bari Howell and Owen Day at CEFAS in Conwy, Wales, have shown that 30 to 40 mg sole can easily be weaned by the SSF larvae diet, with a survival rate of 93%.
Growth was equal to that obtained with Artemia, with average specific growth rate of 5 to 10% a day. Weaned sole of 0.8 g achieved optimal growth and feed conversion efficiency when fed a daily feed ration of 12 and 5% body weight, respectively.
Whitefish has become an important stocking species and a promising candidate for intensive farming - specially in Finland, but also in other European countries such as Germany. Weaning whitefish was a problem, but it could be carried out with very expensive feed. Preliminary experiments with whitefish larvae, performed by Dr Juha Koskela at the Finnish Game & Fisheries Research Institute at Valkola, have shown good acceptance and palatability of the new SSF larvae feed on 12 to 15mg larvae.
"The specific growth rate was more than 7% at 14 to 18 C, and survival was 95% or higher in a 56-day trial with final weight of about 3.4 g," reports SSF. "No morphological signs of nutrient deficiency were found, and the fish looked healthy and showed normal shoaling behaviour."
SSF says that the feed has also shown promising results on cod. High attractability and easy intake was demonstrated by Drs Gunnar Nyhammer and Erling Otterlei at the High Technology Centre of the Department of Fisheries & Marine Biology in Bergen. "They started with cod larvae of 62 to 65 mg and performed the trial at 10 C," explains SSF. "The specific growth rate was about 10% in a 21-day experiment, with final weight of about 0.5 g. Survival was about 64% and loss of fish was mainly due to cannibalism. This fact may have overestimated the growth rate as the biggest fish is the most likely to survive."
Details: The Herring Oil and Meal Industry Research Institute (SSF), Bergen, Norway. Fax: +7 55 91 60 33, e-mail: anders.aksnes@login.eunoet.no
(article in Fish Farming International, December 1997, Vol. 24, No. 12)