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A study was conducted to evaluate tissue storage and mobilisation of L-ascorbic acid (AA) in the Siberian sturgeon (Acipenser baeri) fed three different experimental diets. The three treatments consisted of a diet devoid of vitamin C (diet A0) and two diets supplemented with equivalent of 300 mg AA kg(-1) in the form of either silicone-coated ascorbic acid (diet SC) or of ascorbyl-2-polyphosphate (diet AP). During the first phase (4 months) of the trial, six batches of 130 Siberian sturgeon (initial body weight: 25.5±0.5 g) each were fed one of the three diets in duplicate. During the second phase (3 months), fish from groups SC and AP were switched to diet A0 and those fed diet A0 during the first phase were switched to diet SC. Irrespective of the dietary treatment, growth rates were not significantly different from each other. At the end of phase I, in all tissues studied, total ascorbic acid (TAA) concentrations were higher in Siberian sturgeon fed diet AP than in the other two groups. During phase II, tissue ascorbate depletion was also higher in the AP group than in the other two groups. Transfer of the AA-free diet fed group onto a diet supplemented with 300 mg AA kg(-1) (diet SC) led to a slight increase in the TAA concentrations in all tissues. Blood plasma tyrosine concentrations were not significantly different between the three groups. Whole-body collagen levels were affected by dietary AA levels or forms at the end of phase I; the differences were not significant at the end of phase II. Muscle collagen levels were slightly affected. L-Gulonolactone oxidase activity was found in the kidney of Siberian sturgeon, but not in the liver. The ascorbyl-2-polyphosphate appears to be either better utilised by Siberian sturgeon, like in many other teleosts, or more stable than the silicone-coated AA during food processing and storage. Presence of L-gulonolactone oxidase activity in Siberian sturgeon kidney combined with the absence of gross scorbutic signs in AA-free diet fed groups expressing very good growth rates suggested no need of dietary AA byA. baeri.

A method for the direct measurement of plasma amino acid flux, in rainbow trout, using the continuous infusion of L-[U-(14)C]-leucine with ALZET mini-osmotic pumps implanted into the peritoneal cavity, was developed. The fish were fed successively on three different diets (a commercial control diet, a semi-purified diet and a purified diet) during the 4 weeks of experiment. The amounts of radioactivity in the free pool and the protein of both the plasma and skin mucus were measured in these fish. The total flux of leucine was calculated either from the specific activity of leucine in the plasma (61.8 mg leucine. 100 g(-1).d(-1)) or from the amounts of labelled and unlabelled leucine flowing into the skin mucus protein (61.5 mg leucine. 100g(-1).day(-1)). The total plasma flux was not affected by changes in the diet. The contributions of total leucine oxidation and whole body protein turnover to plasma leucine flux (80% and 20% respectively) were estimated in fish fed the semi-purified diet.

In wild fish, gonad maturation and spawning induce modifications in feeding behaviour and dynamics of body stores which are possibly responsible for metabolic disorders. Conversely, food manipulations can modify reproduction of captive female broodstock. A restricted diet during early stages of the life cycle delays the first maturation age, a quantitatively restricted food supply during the stages of oocyte differentiation reduces the egg number, while a reduction of food levels during the last phases of oogenesis has only a small effect on egg size, composition and hatchability. During the spawning period, salmonid female broodstock seem to be more able to utilize carbohydrates than immature fish, they valorize the energy brought in by fats and have low quantitative requirements for proteins (28%). On the other hand, Red Sea bream broodstock have higher needs for proteins (45%).The incorporation into diet of liposoluble vitamins and essential fatty acids is necessary for normal reproduction, but (n-6) fatty acids seem to play a more important role than in juveniles. Although the effects and physiological role of carotenoids are not yet well known in salmonids, they are necessary for normal development in Red Sea bream. Although little work has been done on the effects of mineral nutrition, special attention must be paid to trace elements, manganese in particular.The major part of this review concerns female broodstock, since very little interest has been devoted to males.