Optimizing feeding strategies with dry diets to balance growth and reproductive quality in crucian carp (Carassius carassius) for conservation-oriented aquaculture

Abstract

Two commercial dry diets were fed to Carassius carassius (L.) juveniles for 60 days at 25°C, each at feeding intensities of 2.0%, 2.5%, or 3.0% of fish biomass per day, to determine the effects of feeding intensity on fish growth, condition factor K, incidence of body deformities, chemical body composition, and gonadal development. Growth of fish and K values were positively influenced by the feeding intensity; likewise fat content in fish bodies. In contrast, ash content was influenced negatively. Intensities of 2.5% and 3.0% resulted in high final incidence of body deformities (range 28.6-76.2%), whereas at 2.0% only 1.9-8.6% fish with deformities were recorded. Gonadal development increased with fish size and feeding intensity, with the most advanced reproductive stages in groups fed at 3.0% biomass/day. Feeding intensity exerted no negative effects on the histological structure of male and female germ cells. However, excessive feeding was associated with a reduced gonadosomatic index (GSI). Our results indicate that feeding at a level slightly below satiation (2.0-2.5% biomass/day) offers the best balance between fish growth, avoidance of body deformities and reproductive readiness. These findings provide guidance for the development of standardized protocols for aquaculture-assisted conservation of C. carassius, including stocking programs and captive breeding efforts.