Relationship between atresia, fish size and condition in Icelandic cod (Gadus morhua L.)

Abstract

Cod is a determinate spawner, with a high potential fecundity. That is, a large definite number of oocytes start maturing prior to spawning. Environmental factors, such as water temperature and food availability have strong effects on nutritional status and fish size. Accumulation of energy prior to spawning is important, as food intake during spawning is minimum. Fecundity is a changeable process that can be adjusted to the condition of the fish. Under favorable circumstances potential fecundity may be equivalent to the number of eggs spawned during the spawning season. When the environmental conditions are unfavorable some or all, developing oocytes included in the potential fecundity estimate may be lost through resorption from the ovary, a process known as atresia. Atresia seems mainly to be initiated under low nutritional status prior to spawning. The relationship between atresia and oocyte diameter is negatively related. As the oocyte diameter increases during the spawning season, occurrence of atresia decreases.