The effect of different pH and photoperiod regimens on the survival rate and developmental period of the larvae of Portunus pelagicus (Decapoda, Brachyura, Portunidae)

Crustacean larval development occurs within a narrow range of environmental parameters (Sastry, 1983). Among the abiotic characteristics that influence the developmental period and survival rate of the larvae, pH and photoperiod are of great importance. High and low levels of pH are known to adversely affect the physiology of the animals due to the increased amounts of ammonia and nitrite (Oanh et al., 2000). High values and sudden fluctuations in pH are found to cause disease outbreaks (Cheng and Chen, 1998) and stress (Oanh et al., 2000), respectively in crustacean larvae. A pH around 8.5 was found to be the optimum for larval rearing of the mud crab Scylla paramamosain (Nghia et al., 2007). Another important parameter that decides the survival and developmental period of crustacean larvae is the period of exposure to light or darkness. Other aspects of behaviour and physiology that are influenced by lighting includes entrainment of physiological processes to circadian cycles (Dalley, 1980), endocrine control of metamorphosis (Eagles et al., 1986), initiation of ecdysis (Waddy and Aiken, 1991), cannibalism (Hecht and Pienaar, 1993) and swimming activity and hence metabolism (Gardner, 1996).