The effects of dietary medium-chain fatty acids (MCFA) on survival, growth and fatty acid composition of first-feeding carp larvae were investigated in two 21-day feeding trials. In trial 1, one diet CO was supplemented with 10% coconut oil, two diets, M1 and M2 with 1.7 or 4.2% interesterified medium-chain triacylglycerols (MCT), and two other diets T1 and T2 with 1% tricaprylin and 0.7% tricaprin, or 2.5% tricaprylin and 1.7% tricaprin. The five diets were made isolipidic (18% of dry diet) with triolein and compared to a control diet without MCFA. With a low dietary level (1% of dry diet) of caprylic acid (C8:0), final survival and mean weight of larvae fed CO, M1 and T1 were not significantly different from those of control (68 ± 6% and 62 ± 8 mg, respectively). In contrast, with a high dietary C8:0 level (2.5% of dry diet), final survival and mean weight of larvae fed M2 and T2 were markedly decreased (23 ± 2% and 40 ± 8 mg, respectively), without effect of the form of supply. In trial 2, larvae were fed six diets with graded tricaprylin contents (from 0 to 10% in diet). Survival was not significantly affected but growth was decreased by C8:0 levels higher than 2% of dry diet. Fatty acid composition of larval total lipids revealed high levels of lauric and myristic acids in larvae fed coconut oil. Deposition of C8:0 and capric acid (C10:0) was low after MCT feeding, but depended of the form of supply, being higher with pure than with interesterified MCT. Relatively high amounts of C8:0 and C10:0 were recorded in total lipids of larvae fed 10% tricaprylin. It is concluded that high levels of caprylic acid decrease growth but that low levels are well utilised by carp larvae, irrespective of the form of supply.

With the aim of improving dry diets for first feeding of Heterobranchus longifilis larvae, the effect of dietary lipid sources on growth rate, survival rate and fatty acid composition of fry from 2 days up to 17 days of age was evaluated. Six feeding regimes were tested: Artemia nauplii which served as a reference, and 5 experimental dry diets differing only by the lipid source. The different oils used for the different experimental diets were the following: cod liver oil, palm oil, copra oil, peanut oil and cotton seed oil. Each diet was tested on duplicate groups of 400 larvae placed in the 40 l tanks of a recirculating system (27-29 °C) and fed to excess six times per day every 4 hours. Separation and identification of the fatty acids of diets, eggs and fry were carried out by gas-liquid chromatography. After 15 days of feeding, survival rates were high for all treatments (71-87%) and did not differ significantly. By contrast, growth rates were largely influenced by the feeding regime. Fry fed with Artemia were significantly bigger (289 mg) than those fed artificial dry diets (79-115 mg). However, it was found that the specific growth rate of fry fed Artemia was superior to that of fry receiving dry diets only for fish of less than 50 mg body weight, indicating that Artemia presents a nutritional advantage only for fry at their youngest stages of development (first 6 days of feeding). Among the artificial dry diets, the best results were obtained with diets containing palm or copra oil, the lowest growth rate being observed with the cod liver oil diet. Peanut and cotton seed oil diets led to intermediate results. The fatty acid composition of the whole fry reflected that of the experimental diets. All together, the results indicated the existence of an optimal ratio between n-3 and n-6 fatty acids for covering essential fatty acids requirement of the fry. Growth rates tended to be reduced by an excess of n-3 fatty acids (cod liver oil) or by an excess in n-6 fatty acids (cotton seed oil) as well. Evidence of the occurrence of HUFA (20:4n-6 and 22:6n-3) biosynthesis are given.

The suitability of two commercial dry diets for rearing Coregonus lavaretus larvae was tested in a 58-day experiment. A diet of live zooplankton was used for comparison. The trials were conducted at water temperature of 12 °C in 800 l tanks, with a stocking density of 10 000-25 000 larvae per tank. Diets were evaluated by means of growth and liver histological analysis. Best growth was obtained with zooplankton, but one of the two dry diets (TetraWerke Az 20) also resulted in satisfactory gowth. Examination of liver structure using light and electron microscopy revealed no nutritional pathology for larvae fed with dry diet Az 20. Histological diagnosis presented evidence for a close association between hepatic protein synthesis and larval growth. From the data of the present study it can be concluded that a large-scale rearing of larvae of Coregonus lavaretus exclusively on dry food, is feasible.

A low cost artificial diet was formulated from materials which are locally available in Africa. The diet utilized cowpea, sorghum and corn instead of pinto bean and wheat which are widely used in the USA. The new diet was as satisfactory as the pinto bean diet for all the biological criteria tested. On a pinto bean diet, pupation and eclosion required 14.3 ± 1 and 26.3 ± 1 days, respectively. On the cowpea diet, 14.6 ± 1 and 26.9 ± 1 days were required, respectively. Ninety-eight per cent of adults eclosing on each diet were viable. Females eclosing on the cowpea diet laid 739 ± 53 eggs of which 59 ± 2% hatched. On the pinto bean diet, 774 ± 62 eggs were laid per female with 61 ± 2% hatching. Pupal weights were 526 ± 22 and 537 ± 28 mg when larvae were reared on the pinto bean and cowpea diets, respectively. Food consumption and utilization by larvae reared on the new diet were comparable with those of larvae reared on the popular pinto bean diet.