Ontogeny of the capacity for homeoviscous adaptation in white sturgeon (Acipenser transmontanus)

Abstract

AbstractMost fish species tolerate a narrower range of temperatures during their early life history. To ascertain whether this might be related to development of the capacity to regulate membrane fluidity (homeoviscous adaptation), we examined the fatty acid composition of tissue phospholipids from developing white sturgeon eggs, embryos, and prefeeding larvae incubated at temperatures both within the range of natural spawning temperatures (14°), and above (20°) and below (8°). Mortality was highest at low temperature, with the greatest losses prior to neurulation. High temperature also resulted in increased mortality relative to 14°, with peak mortality between neurulation and hatch. At a constant temperature of 14°, significant changes in the fatty acid composition of tissue phospholipids were observed during development, but the patterns of change were altered by development at low and high temperature. Contrary to homeoviscous theory, embryos incubated at low temperature exhibited a decline in the ratio of unsaturated to saturated fatty acids (U/S ratio). In contrast, posthatch larvae exposed to low and high temperature exhibited, respectively, higher and lower U/S ratios than larvae maintained at 14°, implying that the capacity for homeoviscous adaptation is acquired at the time of hatch. Although the lack of a homeoviscous response by embryos may account for low survival at temperature extremes, the specific influences of the observed changes in phospholipid fatty acid composition on the biophysical properties of cell membranes remain to be determined. © 1993 Wiley‐Liss, Inc.