Fecundity, Atresia, and Egg Size of Captive Atlantic Cod (<i>Gadus morhua</i>) in Relation to Proximate Body Composition

Abstract

Captive Atlantic cod (Gadus morhua) were fed at four ration levels (starvation, maintenance, moderate, and excess) for periods of 6–9 mo prior to and during spawning. At the end of the experiment, water, protein, glycogen, and fat contents of the liver, white muscle, and ovary were estimated. The depletion of the white muscle and liver was related to oocyte maturation and in particular to the proportion of eggs spawned (PES). The influx of protein into the ovary, the mean hydrated egg diameter, and the egg dry weight all reached maximum values at 10% PES and subsequently declined. Mean vitellogenic oocyte diameter was small prior to spawning but rose to a maximum at PES = 10%. Cod with high condition factors produced more previtellogenic oocytes and used a larger fraction during vitellogenesis. Actual fecundity of specimens deprived of food during the spawning period was between 20 and 80% of the potential fecundity depending on the nutritional status of the fish. Intensity of atresia in moderate ration fish increased from 0% at PES = 0% to 33% at PES = 80%. Estimates of durations of α-atretic vitellogenic oocytes varied between 10 and 13 d at 8 °C assuming a spawning period of 50 d.