Does salinity affect somatic growth in early juvenile Atlantic croaker, Micropogonias undulatus (L.)?

Abstract

Factors affecting recruitment of fishes remain one of the most studied but least understood issues of fisheries science. Understanding the causes of recruitment variability remains elusive because factors that affect the growth and survivorship of young fishes are complex and dynamic. Here we focus on the influence of salinity on growth of early juvenile Atlantic croaker, Micropogonias undulatus under laboratory conditions as part of a larger study to relate short-term fluctuations in growth rates of young estuarine-dependent fishes with variability in abiotic environmental factors. Body growth of juvenile Atlantic croaker was significantly (P<0.001) different among all of the three salinity treatments with growth in 5‰>20–5‰=20‰. A linear response to the changing treatment suggests an additive effect of changing salinity on body wet weight (WW) growth. Juvenile Atlantic croaker in the 5‰ treatment grew in WW by a factor of 3.88 relative to initial WW. Fish in the 20–5‰ treatment grew in WW by a factor of 2.90, while fish in the 20‰ treatment grew in WW by a factor of 2.17. Otolith diameter also varied significantly with salinity, and there was a significant positive relationship between changes in body WW and changes in otolith diameter growth (r=0.68, P<0.02, n=12). The correlation between body and otolith growth justified our use of otolith data to infer that substantial fluctuation in the early growth of early juvenile Atlantic croaker from field collections was inversely cross-correlated with salinity and water temperature. Assuming that the probability of survival during the nursery period increases as postlarval fish grow, salinity-induced plasticity in growth rates implies that the site and habitat into which post-larval fish settle can potentially influence recruitment dynamics. This study demonstrates that there is the potential for fluctuations and spatial variability in salinity to cause significant variability in short-term growth rates for juvenile fishes within estuarine nursery areas.