Comparison of the nutritional status of goldfish ( Carassius auratus) larvae fed with live, mixed or dry diet

Abstract

The aim of this work was to study the influence of three diets on the nutritional status of goldfish larvae. The evaluation criteria for food quality were: growth and survival of the larvae, proteolytic activity of a trypsin-like enzyme as well as the structure and ultrastructure of the hepatopancreas. Immediately after the resorption of the yolk sac, the goldfish larvae were distributed into 9 rearing tanks (700 larvae each) under constant photoperiod (L:D 16:8) and temperature (24°C). The fish were offered three different diets: D1 ( Artemia nauplii), D2 ( Artemia nauplii + 50% dry feed) and D3 (dry feed). After a 21-day experiment, best results for growth and survival were obtained with diets D1 and D2 ( P<0.001). At the end of the second week, growth rate was high in the groups fed with diet D1, intermediate in the D2-fed groups and low in the D3-fed groups. These results can be directly related to the differences in tryptic activity in the goldfish larvae ( P<0.001). During the third week, however, the best specific growth rate and highest tryptic activity were observed in the groups fed the mixed diet. Tryptic activity in larvae fed dry feed was low during the whole experiment (lower than 0.03 IU/mg of larvae instead of up to 0.09 and 0.08 IU/mg of fish in groups fed with Artemia and mixed diets). The liver and hepatocyte structures of the larvae fed D1 and D2 diets showed no signs of anomaly, contrary to what was observed in D3-fed larvae (irregularly linked hepatocytes, numerous blood vessels, absence of Golgi apparatus but high lysosome number in the hepatocytes).