Comparative experiments on starter diets for grass carp and common carp

Abstract

The influence of different compound diets and live zooplankton on growth and survival of two species of cyprinid larvae was compared. In common carp larvae fed exclusively on dry diets high mortality occurred in most cases; exceptions were fish fed Ewos C 20 starter diet (12%). However, growth after 16 days of feeding was impaired in the latter groups (16.8 mg individual body weight) compared to groups offered zooplankton (28.9 mg) or other dry diets (38 mg). Grass carp larvae performed far better when fed the same starter feeds. The survival was 78–79% after 19 days of rearing, and individual body weights were 62.7±35.4 and 105.8±27.3 mg with diets based on Polish and French (IFP) yeast, respectively. In a comparable period grass carp larvae offered live zooplankton (cladocerans) grew to 30±14.4 mg and survival was 91%. One of the test diets contained the antibiotic tetracycline. Fish weight and survival were significantly influenced by addition of antibiotic to the grass carp larval diet, particularly during the second phase of rearing from days 20 to 92. Fish grew to 8.2 g average body weight within 3 months of rearing in the case of the group having the best growth rate in the initial phase of the trial. It has been proved that freeze-dried fish tissues, muscle and roe, are detrimental ingredients in cyprinid larval diets, and high lipid diets are also unsuitable for fry. Amino acid analysis of diets revealed that other nutritional factors set the quality criteria for the larval diet of these specific cyprinids.