Osmotic responses of eggs and larvae of the Pacific herring to salinity and cadmium

Abstract

. Yolk osmolalities decreased, after hatching of the larvae, to approximate those levels attained between 100 and 250 hr. An hypothesis is presented whereby minimum osmotic work is defined on the basis of isosmotic relations existing between yolk, perivitelline fluid, and incubation medium. This leads to the description of a range of salinities defined in terms of osmoregulatory scope. At the 5 ~ test temperature, incubation salinities associated with maximum osmoregulatory scope (13.2-19 %o) correspond closely to the range of salinities providing maximum or near-maximum hatches of viable larvae. The presence of a salinity-temperature interaction and its influence on the association between osmoregulatory scope and production of viable larvae is suggested as a mechanism underlying and providing the recognized plasticity of Pacific herring egg development. In a companion study involving cadmium as a contaminant, eggs !ncubated at 20 %~ S were exposed to 0, 1 or 10 ppm Cd in 5, 20 or 35 0/00 S for 48-hr periods at six stages of development between fertilization and hatching. Cd exposure resulted in a reduction in osmolality of perivitelline fluid. Reduction was greater in higher Cd concentrations and in eggs transferred to higher salinities. An hypothesis is presented to explain observed effects of Cd exposure on some physical properties of teleost eggs, including reductions in perivitelline fluid osmolality and egg volume. Finally, newly hatched (0-, 3-, 6-and 9-day old) larvae from eggs incubated at 20 %~ S (8.5 ~ were exposed to salinities from 0 to 50 %o for a period of 72 hr. Median tolerance limits (72-hr) were 2.8-5.2 %o for low salinities and 33-35.8 ~174 for high salinities. No trends in salinity tolerance were noted amongst the four ages of larvae. The data suggest that natural larvae entrained in sea water would be susceptible to salinity-induced mortality in salinities greater than about 20 %o. However, this conclusion is subject to confirmation in view of the low/low-high/high salinity-temperature interaction previously noted in relation to egg development, and its possible continuing influence in larval stages.

Cold hardiness of the eggs of the plaice, Pleuronectes platessa

“…It has been shown for several teleosts egg that changes in the ambient seawater salinity at a constant temperature were followed by changes in the perivitelline fluid after about 4-6h (Lasker and Theilacker 1962;Holliday 1965Holliday , 1969. In Pleuronectes platessa a new steady state in yolk osmolality after a medium osmotic stress were reached in less than 24 h (Holliday and Jones 1967), in contrary to the herring species where this took about 100-250 h (Holliday and Jones 1965;Alderdice et al 1979). Because the chorion is highly permeable to water,-ice crystal growth and increasing brine osmolality on the surface of the egg will withdraw water from the perivitelline fluid.…”

“…4). This variation could be the result of an increased osmolality in the perivitelline fluid with increasing external salinity, as the measured total egg content includes both the yolk and the perivitelline fluid (Alderdice et al 1979). Holliday and Jones (1967) also demonstrated differences in the osmolality of the "yolk" between exposure salinities.…”

Embryonic development and metabolic costs in Gulf killifish Fundulus grandis exposed to varying environmental salinities

“…Rao (1974) determined that California killifish embryos had a longer mean TH and reduced hatching percentages of 33.3 and 51.4%, respectively, in freshwater compared to 76.8 and 75.8% for 5 g/L. Minimum osmotic effort occurs most often when the incubation medium is isotonic with the yolk and perivitelline fluids (Alderdice et al 1979). At tonicities outside of this optimal range, energy may be diverted away from growth and development of embryos (Rao 1974;Boeuf and Payan 2001;Sampaio and Bianchini 2002).…”

Salinity Tolerance of Fertilized Eggs and Larval Survival in the Flsh Sillago sihama

“…It is, therefore, suggested to transfer eggs as late as possible, wherever eggs are needed to be transferred from spawning to incubation tanks. Minimum osmotic work for larvae was also suggested to be associated with the maximum salinity tolerance (Alderdice et al, 1979).…”