Too Hot or Too Cold? How Pacific Sardine Respond to Changing Temperatures

Coastal pelagic fish species such as Pacific sardine (Sardinops sagax) undergo large fluctuations in abundance that end up affecting the marine ecosystems and economies of countries worldwide. Climatic fluctuation has been suggested as a strong driver for these population booms and busts, but little work has been done to understand the effect of temperature on sardine physiology.  In this study, our objective was to understand the optimal physiological temperature range of Pacific sardine collected April-May and November-December off the southern California coast.  These sardine likely represent the hypothesized “cold” stock of sardine.  We subjected the sardine to slowly changing temperatures ranging from 9°C to 25°C.  We sampled sardine at 9°, 11°, 13°, 15°, 17°, 19°, 21°, 23° and 25°C for blood plasma, liver, heart, and white muscle tissue.  We measured the enzyme kinetics of LDH in white muscle tissue and CS in heart tissue, the gene expression of heat shock proteins and immune genes in liver tissue, and levels of cortisol in blood plasma to identify an optimal temperature range for sardine. These results will provide insight into how Pacific sardine respond to fluctuating temperatures and into their optimal temperature range.