Characterization of the Atlantic cod (Gadus morhua L) eggs for estimation of spawning time and proportion of spawning females

Abstract

A set of eggs from first time spawning Atlantic cod (Gadus morhua L) was investigated for the understanding of variations in egg sizes, e.g. with time in the spawning season, daily inter and intra variations, daily distributions and spawning time (early, mid, and late spawning season). Furthermore, the egg sizes were characterized for the estimation of spawning time and the proportion of spawning females in tanks. The egg sizes indicated a decreasing trend between batches spawned early, mid and late in the spawning season. Daily inter and intra variations indicated a decreasing trend towards late the spawning season. The daily egg size distributions indicated high variability during the early spawning season and this variability tended to decrease in batches spawned late in the spawning season. Early, mid, and late phases of the spawning season were categorised through time elapsed since the beginning of spawning and by total daily production of eggs. This study also reviewed whether the size of a fish egg is an indicator of quality and also whether cod production of eggs of high variability in size, amount and quality over the whole spawning season is a reproductive strategy. It has been observed that among many other determinants of egg quality, size is an important indicator as the size of an egg determines the amount of yolk and the size of larvae at hatching. Cod produces eggs of high variability in the season as a strategy of maximizing production efficiency and assuring survival of its offspring.