Variation in egg buoyancy of Baltic cod Gadus morhua and its implications for egg survival in prevailing conditions in the Baltic Sea

Abstract

In the Baltic Sea successful spawning of cod is restricted to the deep basins, and egg buoyancy is regarded as a major factor that allows eggs to avoid the stressful oxygen conditions that often prevail in the deep layers. In this study eggs of 3 to 5 yr old spawners (the basis of the spawning stock of Baltic cod Gadus morhua L. nowadays) maintained neutral buoyancy at a salinity of 14.5 i 1.2 ppt, with great variation among eggs from different females. Egg buoyancy was significantly correlated with yolk osmolahty and chorion thickness and weakly correlated with egg size. Measurements of egg buoyancy in successive batches from the same female indicated that egg buoyancy increased with batch number. The significance of neutral buoyancy for cod egg survival in prevailing conditions in the Baltic was evaluated by comparing the ability of eggs to achieve neutral buoyancy in the Baltic cod spawning areas during June of the 6 years 1977-1980, 1982 and 1987. The results suggest that the ability of eggs to maintain neutral buoyancy should be included in attempts to find explanations for fluctuations in recruitment of Baltic cod.

Reproduction of Baltic cod, Gadus morhua (Actinopterygii: Gadiformes: Gadidae), in the Gotland Basin: Causes of annual variability

“…This is a habitat where early development of the spawned cod eggs can be adversely affected. Taking into account the size and the condition of the spawning stock (larger females produce larger and more buoyant eggs then smaller ones) and that during stagnation periods viable cod eggs are observed (Grauman 1984, Nissling et al 1994, this hypothesis suggests that if the URV is smaller the cod eggs have higher probability of survival and production of viable larvae. Such assumption also allowed constructing continuous time series of quantitative indices of the environmental conditions in the Gotland Basin where SRV is observed less frequently, especially in the northern part.…”

Platichthys solemdali sp. nov. (Actinopterygii, Pleuronectiformes): A New Flounder Species From the Baltic Sea

“…The relatively few marine fish species that thrive in the Baltic Sea exhibit adaptations to the low salinity and temperature they have encountered (Nissling et al, 2002(Nissling et al, , 2006Hemmer-Hansen et al, 2007;Florin and Höglund, 2008;Nissling and Dahlman, 2010;Guo et al, 2015). Some of them show ecological adaptations allowing the spawning of pelagic eggs that can maintain neutral or positive buoyancy in deep basins, where salinity is higher than in coastal waters (Nissling et al, 1994(Nissling et al, , 2002Vallin and Nissling, 2000;Nissling and Dahlman, 2010). Other species have changed their life-history strategies by switching to coastal spawning of demersal eggs (Nissling et al, 2006).…”

Osmotic condition, buoyancy change and mortality in larval cod Gadus morhua. A bioassay for assessing near-term mortality

“…Kjesbu et al 1992, Nissling et al 1994, Ponwith & Neill 1995. These factors can be com-DISCUSSION plex (Sclafani et al 1997); however, the magnitude of the density changes induced by these factors are much Since changes in larval density resulting from nonlower than those associated with osmotic breach and osmotic factors (i.e.…”