Comparison of rearing performances and intermuscular bone number in the mirror and nude genotypes of common carp ( Cyprinus carpio L.) in a controlled field test in Madagascar

Nude carps, a genotype of common carp which are devoid of scales, have been banned from farmed populations of carp in Europe due to both the lethal effect of the N (nude) gene when in homozygous state, and to the negative pleiotropic effects on growth and survival (especially in harsh conditions) of this same gene in the heterozygous state, which produces the nude phenotype. In Madagascar, where climatic variations are less extreme than in Eastern Europe, the nude phenotype is valued both by farmers and consumers, for its good growth and supposed low number of intermuscular bones. We performed an on-farm experiment using a “common garden” design to control environmental variation, in order to compare the growth and survival, as well as the number of intermuscular bones of nude carp to two other common scale cover phenotypes of the same species, the mirror and scaly carps. We found that survival of nude carps was lower or equal to that of mirror carps at all stages of the farming process, while growth performance was lower than that of mirror carps in some ponds only. Globally, the biomass production per fish stocked was always lower in nude carp compared to mirror carp. The number of intermuscular bones was the same in nude, mirror and scaly carps. We conclude that as in Europe, it would be valuable to farm mirror rather than nude carps, as the supposed benefits of the latter are not supported by our experiment in typical Malagasy farming conditions. Keywords: Nude carp, Growth, Survival, Pleiotropy, Intermuscular bones