The Effects of Temperature, Age, and Acclimation to Salinity on the Survival of Farfantepenaeus paulensis Postlarvae
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Abstract.— Salinity tolerance limits during the ontogenetic development of Farfantepenaeus paulensis postlarvae (PL) were determined at different temperatures. Initially, PL 10, 20, 30, 40, 60 and 80 maintained in 30 ppt (parts per thousand) salinity, 22‐25 C, were directly transferred to 15 combinations of salinity (2, 5, 10, 20 and 30 ppt) and temperature (15, 20 and 30 C) for 96 h. Irrespective of age or salinity, higher survival rates were registered at 25 C. PL 10 suffered high mortality, especially at low salinities combined with low (15 C) or high (30 C) temperatures. From PL 20 to PL 40, an increase in survival was observed in all combinations. For PL 60 and 80, tolerance to low salinity was reduced, suggesting that PL have a maximum age by which they are able to develop adaptability to low salinities. In general, the effect of temperature contributed more significantly to mortality in PL 10 and PL 30, but its influence decreased afterwards. From PL 40, salinity becomes the main factor determining mortality. In order to examine the effects of acclimation to salinity on the tolerance limits, a second set of experiments was performed with PL 5, 10, 15 and 25 acclimated to 2, 5, 10, 20 and 30 ppt, 25 C, over a 5‐d period. Postlarvae were then transferred to different salinity levels (2, 5, 10, 20 and 30 ppt) and kept for 96 h. High mortality of PL 10 occurred after direct transfer from high to intermediate/low salinity levels. Although the acclimation to salinity increased survival, it was still poor. An increase in the salinity tolerance was observed from PL 15 to 30, even with no acclimation. Results indicate that PL 10 do not have a fully developed osmoregulatory capacity to cope with low and/or abrupt changes of salinity. It is recommended that non‐acclimated PL 10 should only be released in environments with salinity at or above 20 ppt. If acclimation is carried out, PL may be released in salinities above 10 ppt. The release of PL 10 in salinities below 5 ppt may result in mortality rates of up to 70%. The best age for the release of non‐acclimated F. paulensis PL in environments with low and/ or wide fluctuations of salinity would he PL 15‐30.
