Some effects of temperature and salinity on laboratory-reared eggs and larvae of Polydactylus sexfilis (Pisces: Polynemidae)

Effects of temperature and salinity on eggs and yolksac larvae of Polydactylus sexfilis (Cuvier and Valenciennes) were examined in laboratory experiments. Data on developmental rates as influenced by temperature are presented. Larval length at 95% yolksac absorption was maximized between 23.8 and 28.6°C. Based on the development of functional eyes and jaws, larvae were judged capable of feeding before the yolk was completely absorbed. Larvae incubated at intermediate temperatures also had larger amounts of yolk remaining when eyes and jaws were judged functional. Temperature and salinity effects on hatching success, survival at the end of the yolksac stage, and morphological abnormalities were studied in a 10 × 5 (temperature × salinity) array of treatments. In 34‰ sea water, normalized larval survival at the end of the yolksac stage was greater than 50% between temperatures of 21.9 and 28.0°C. Larval survival decreased at lower temperatures and salinities. Proportions of abnormal larvae increased at temperature and salinity extremes, and normal development was maximized between 26 and 34‰. Larvae (74 h after fertilization) were more tolerant to extreme high temperatures than were newly fertilized eggs. Upper salinity tolerance limits of 42-h larvae were greater at 26.2°C than at 23.5 or 29.2°C, and lower salinity was less tolerated at the two extreme temperatures. Based on the results, recommended temperatures and salinities for rearing P. sexfilis eggs and early larvae are 24–28°C and 26–34‰.