Effects of salinity on growth, fatty acid synthesis, and expression of stress response genes in the cyclopoid copepod Paracyclopina nana

Abstract

In marine ecosystems, salinity fluctuations are critical in modulating energy balance, inducing stress proteins, providing reproductive success and affecting the distribution of copepods. Salinity induces osmotic stress in organisms when they are not in their optimal condition and the stressful status increase the energy demand required for osmoregulation, which in turn reflects in all biological processes. Effects of salinity stress on life history traits and tolerance are species-specific. In this study, we used the estuarine cyclopoid copepod Paracyclopina nana to understand the responses towards the hypo (5ppt) and hypersalinity (25 and 30ppt) conditions, and compared that with the control (15ppt). We investigated the life cycle parameters (e.g. growth and fecundity), fatty acid (FA) synthesis, lipid accumulation (as lipid droplets [LDs]) and modulation of heat shock proteins (hsps) in response to salinity stress. As a result, life cycle parameters and FA synthesis, LDs, and modulation of hsps were found highly dependent on salinity changes in P. nana. Particularly, hypersalinity resulted in developmental retardation, reduced fecundity, decreased FA synthesis, a drop in lipid accumulation, and modulation of stress response proteins, suggesting that P. nana devoted increased energy to cope with the osmotic imbalance due to salinity stress in hypersalinity conditions. This finding provides a better understanding of how salinity affects in vivo endpoints and the relevant molecular responses in estuarine copepods. Statement of relevanceWe envisage that this manuscript will be helpful to understand salinity-dependent lipid composition changes in copepods and optimize the optimal salinity for the mass culture for this species.Considering the small size (~600μm) of P. nana and its potential as live feeds for finfish larviculture, the present findings have considerable importance for the aquaculture industry.