The Buoyancy and Vertical Distribution of Eggs of Sprat (Sprattus Sprattus) and Pilchard (Sardina Pilchardus)

Abstract

Observations on the density of pelagic marine fish eggs have indicated that they are near neutral buoyancy for most of development and have a tendency to become denser towards hatching (see Russell, 1976). However, most of this information has been based on limited laboratory observations on the relative buoyancy of eggs; only a few experiments have given more precise estimates of the absolute density of eggs based on the salinity of water in which they are neutrally buoyant (e.g. Franz, 1910; Sundnes, Leivestad & Iversen, 1965). Recently, a new technique (Coombs, 1981), based on the use of a stable column of continuously graded sea-water concentration has allowed more precise and routine measurements of the density of fish eggs throughout development.

Reproductive output traits of the simultaneous hermaphrodite <I>Serranus scriba</I> in the western Mediterranean

“…Therefore, the potential for osmoregulation in S. scriba is low, implying that the possible underestimation of density is far too small to affect our interpretation (Coombs et al 1985). Not having a large osmoregulatory potential agrees with the highly stable conditions found during the summer (P. oceanica seagrasses only occur in clear waters and are not found close to river plumes).…”

“…We used a 1-m column of water with a stable, constant gradient of seawater salt. Glass spheres of a known density were used to calibrate the system (Coombs et al 1985(Coombs et al , 1990. Fertilized, live eggs were introduced at the top of the column and allowed to settle to the location where the egg was in hydrostatic equilibrium with the surrounding fluid.…”

“…Buoyancy is also as a key variable in drift models, so the position of the egg in the water column and associated changes throughout development are fundamental issues in assessing egg viability and the effects of specific environmental scenarios on egg dispersal (e.g. Coombs et al 1985, 1990, Adlandsvik et al 2001. Spawning events typically occur at the diel time scale, and these affect reproductive success through the probability of fertilization, rates of predation, and dispersion of eggs and larvae (Lowerre-Barbieri et al 2011).…”

The influence of different salinity conditions on egg buoyancy and development and yolk sac larval survival and morphometric traits of Baltic Sea sprat (<i>Sprattus sprattus balticus</i> Schneider)

“…Egg swelling continues as water and ions enter the forming perivitelline fluid until a steady state ensues between the chorion and the increasing hydrostatic pressure (Alderdice, 1988). The change in neutral buoyancy of the eggs has been estimated as corresponding to approximately 2 practical salinity units at a change in ambient salinity of 10 practical salinity units (Coombs et al, 1985), which agrees well with the results of the present study.…”

Influence of some physical and biological factors on the density and vertical distribution of Atlantic halibut Hippoglossus hippoglossus eggs

“…Technical advances in the development of multiple-net plankton samplers has, however, enabled collection of more detailed and precise information on the vertical distribution of ichthyoplankton (e.g. Coombs et al 1981, Haug et al 1984, Solemdal & Ellertsen 1984, Coombs et al 1985. Similarly, improvements of density-gradient columns has allowed better estimates of the neutral buoyancy of live fish eggs (see Coombs 1981).…”