Survival rate and growth in the wild of sea trout (Salmo trutta L.) fry obtained using frozen semen

Abstract The aim of the study was to assess the growth and development of sea trout, Salmo trutta L., fry obtained from frozen, thawed semen after the fish had been released into the wild and were feeding there. The semen was cryopreserved with either methanol (MeOH) or dimethyl sulfoxide (DMSO). Fresh eggs were collected and fertilized with the thawed semen. The control was eggs fertilized with fresh semen that had been kept on ice. The eggs were incubated and reared in a closed recirculating system. The fertilized eggs were counted for visible eye pigment. After rearing, three groups of fish were tagged and stocked into a stream. The fish aged 6 months were caught from the stream. The fish were measured, weighed, identified to which experimental variant they belonged, and their survival rate was estimated. No significant differences in survival rate, length, weight, or condition factor among the control, DMSO, and MeOH groups were noted during larval development in a closed recirculating system. These parameters were also similar in the control and experimental groups after the fish had grow in a natural stream. The use of frozen semen to fertilize fresh sea trout eggs resulted in a normal incubation process, larval stage, and regular fry growth and survival, both under laboratory conditions, and, most importantly, in the wild. The results indicate it is possible to use frozen semen for fry production and the restoration of wild fish populations.