Salinity tolerance, ontogeny of osmoregulation and zootechnical improvement in the larval rearing of the Caledonian Blue Shrimp, Litopenaeus stylirostris (Decapoda, Penaeidae)

Abstract

The ontogeny of osmoregulation was investigated in Litopenaeus stylirostris by studying salinity tolerance and osmoregulatory capacity. Shrimp at different larval and postlarval stages were exposed to various salinities and survival was monitored for 24h. Survival rates exceeded 80% at salinity over 25ppt (750mOsm.kg−1) at all the stages. At salinities below to 25ppt, salinity tolerance was higher in nauplii and zoeae than in mysis larvae. Postlarval stages were able to withstand lower salinities, e.g. 6.0ppt (176mOsm.kg−1) at PL9 stage, but they were more sensitive than larvae to salinities over 35ppt (1035mOsm.kg−1). Zoea and mysis larvae slightly hyper-regulated at all tested salinities. After metamorphosis, postlarvae progressively acquired the adult pattern of hyper-hypo-osmoregulation: At PL9, the estimated isosmotic salinity was 24.5ppt (720mOsm.kg−1); below and over this salinity, animals hyper-regulated and hypo-regulated, respectively. Finally, we determine the effects of lowering salinity at different animal development stages. We conclude that seawater salinity (35ppt) is optimum during larval stages; but for postlarval stages, lowering salinity at 27ppt leads to a better growth in 19days compared to those maintained at 35ppt (1.07mg vs 0.47mg). These results are in agreement with penaeid natural life cycle during which larvae are released in oceanic water while juveniles live in coastal areas where salinity is more fluctuant.