Large water flea ( <i>Daphnia magna</i> Straus) and mealworm ( <i>Tenebrio molitor</i> L.) as potential food sources for rearing common carp ( <i>Cyprinus carpio</i> L.) juveniles indoors

Abstract When rearing common carp fry using intensive technology, expensive rearing feeds can be replaced, or partially replaced, with economically produced live food organisms, which is a solution that is close to a natural one. Natural feeding conditions for common carp ( Cyprinus carpio L.) juveniles were modeled in indoor studies 49 d in length in two consecutive years in Szeged, Hungary. In 2021, feeding Szeged mirror carp advanced fry with a nutritionally complete formulated feed was compared to feeding them large water fleas ( Daphnia magna ) and yellow mealworms ( Tenebrio molitor ) in rations that were adjusted for fish growth. In 2022, Szeged mirror carp and scaled landrace advanced fry fed water fleas and mealworms were compared with the same fish genotypes fed water fleas and complete feed in rations that were adjusted for fish growth. Feeding natural food resulted in significantly larger fish and better values for average daily gain, specific growth rate, feed conversion ratio, and final condition factor in both experiments, confirming that feeding live arthropods results in faster-growing carp fry with better feed utilization efficiency. The carp genotypes had different growth dynamics, with Szeged mirror carp exhibiting faster development and more efficient feed utilization compared to scaled landrace.