Characteristics of gametes of the Atlantic salmon (Salmo salar L.) restored in northern Poland

The study aimed to characterise the gametes of salmon (Salmo salar L.) ascending Polish rivers, the first such characterisation since initiation of the salmon restitution programme in the 1980s. Gametes of ascending salmon were examined in two Polish rivers: the Wieprza in the western part of the Polish Baltic coast and the Vistula in the eastern part. Additional gametes were sampled from salmon maintained in pond cultures at fish farms that had provided stocking material for the restitution programme. Spermatocrit, spermatozoa concentration and motility, egg size and weight, as well as egg membrane resistance were analysed. The parameters studied were found to differ both within individual populations and between them. The high variability of the gamete characteristics bodes well for the salmon population in Polish waters, because it evidences high species plasticity and an ability to adapt to changing environmental conditions. Despite the variabilities observed, the egg and sperm parameters showed values within ranges optimal for salmon reproduction under natural conditions. Sperm quality was found to be largely dependent on environmental conditions affecting the adult males (environmental conditions explained 73.9% of sperm parameter variability), whereas egg quality was mainly related to individual characteristics of the respective female (environmental conditions explained as little as 28.3% of the egg parameter variability).