Gonad development and filleting yield of common carp Cyprinus carpio L. reared in ponds in Eastern France

The processing of 232 common carp Cyprinus carpio made it possible to study the correlation between gonad maturation and filleting yield. The study was undertaken between April and August 1992 and was carried out on 4-year-old carp cultured in extensive ponds. Morphological parameters were recorded and relations between total weight and length, biomass of fillet, and biomass of gonad were determined. The histology of male and female gonads was examined in relation to the gonadosomatic index (GSI: up to 16% for females and less than 11% for males) and condition indices (total K or somatic K1). Filleting yields (32–36% of the total weight) decreased for females just prior to spawning and corresponded to a decline of K1. A rematuration phenomenon was observed, although females weighing less than 1200g were still immature. We suggest avoiding the filleting of large females before spawning and suggest estimating the date of appearance of this stage by referring to the positive correlation established in this paper between the number of degree-days and total fish weight.