Buoyancy variations in eggs of Atlantic cod (Gadus morhua L.) in relation to chorion thickness and egg size: theory and observations

Abstract

Egg specific gravity is a function of egg volume, chorion volume, perivitelline space (PVS) and the specific gravity of chorion and ovoplasm. Experimental studies on cod (Gadus morhua L.), a marine multiple batch spawner, showed that approx. forty per cent of the chorion volume is incorporated between batches and that the chorionic material has a mean specific gravity of 1.20 (range: 1.14-1.35). The chorion volume and specific gravity are low at the end of the spawning period in extremely fecund fish. Specific gravity of ovoplasm was observed to be 1.01 7 in marine eggs and calculated to be about 1.008 in brackish water eggs. Inherent variation in PVS is found to have little influence on egg specific gravity. With the other variables constant, egg specific gravity is inversely related to egg volume supported by studies on single batches of eggs. Measurements on every batch of eggs reveal that the production of large eggs (> 1.3 mm) gives low density eggs initially and high density eggs towards the end of spawning, while the production of small eggs ( < I .3 mm) gives moderate specific gravity. These observations are discussed in relation to vertical distribution of the eggs and reproductive success of recruit and repeat spawners. There are indications that repeat spawners produce larger eggs.

Genetic diversity and condition factor: a significant relationship in Flemish but not in German populations of the European bullhead (Cottus gobio L.)

“…Somatic growth potential of fish can be reduced (Danzmann et al, 1988). Reproductive success can be reduced through lower fecundity, reduction in egg quality or lower sperm quality (Kjesbu et al, 1991(Kjesbu et al, , 1992Rakitin et al, 1999). Additionally, poor condition may also lower the chances of survival (Wilkins, 1967).…”

“…In this paper, we investigated the fitness consequences of such a loss in genetic variation by comparing levels of genetic diversity of bullhead populations and condition factor, a trait which is generally considered as a good indicator of fitness in fish (Danzmann et al, 1988;Kjesbu et al, 1991Kjesbu et al, , 1992Rakitin et al, 1999;Thelen and Allendorf, 2001) and which is easy to estimate (a length-adjusted measure of weight). However, other studies have indicated that, instead of genetic variability, other factors such as environmental conditions may be more important in determining the condition factor of fish populations.…”

Egg size in relation to fertilization dynamics in free-spawning tropical reef fishes

“…Egg density also is known to vary seasonally within species of fishes (e.g., Kjesbu et al 1992). This information indicates that the relationship between egg volume and content is not rigidly constrained, by, for example, effects on the fertilization process or early development, and that fishes have some ability to control variation in egg density.…”

“…Egg density also is known to vary seasonally within species of fishes (e.g., Kjesbu et al 1992 stress and aquarium conditions. Sperm depletion was involved in declines in fertilization success in successive spawnings of the characin, but not in the serranid.…”

Length weight relationship and ponderal index of rainbow trout (Oncorhynchus mykiss W., 1792) from Dachigam stream in Kashmir

“…Somatic growth potential of fish can be reduced (Danzmann et al, 1988). Reproductive success can be reduced through a number of factors like lower fecundity, poor quality eggs and sperms (Kjesbu et al, 1991(Kjesbu et al, , 1992Rakitin et al, 1999). Additionally, poor condition may also lower the chances of survival (Wilkins, 1967).…”