Variability in the growth of isogeneic crucian carp Carassius gibelio langsdorfii

Abstract

Some individuals among fish of one batch grow much faster than others in the same condition. This phenomenon is well known in pond-culture of carp and the superior group in growth is called 'Tobi-koi' or shoot carp. Genetic influence on the diversity in growth rate are examined using fully genetically identical clonal crucian carp which is naturally occurring gynogenetic triploid fish. Ploidy was determined by the erythrocyte size and the number of chromosomes. Identity of clone was determined by scale grafting and electrophoresis. A greatvariation in size and weight was found even in clonal crucian carp, indicating the occurrence of superior group when the fry are reared with food of different particle size and in high densities in a small tank. On the other hand, neither shoot crucian carp nor a great varia-tion in growth was found when the fish were cultured in low densities and given a sufficient amount of food in a larger tank. These results suggest that the occurrence of superior group in a batch is not attributed to the genetic difference but to the environmental or ecological conditions.