Studies to optimise the culture conditions for Penaeis indicus from the Saudi Arabian coast of the Red Sea
On the Red Sea coast of Saudi Arabia ponds utilising seawater drawn from wells have an average salinity of 43%o and temperatures ranging from 23-33°C. The present study has demonstrated that yields of up to 4.3 tonnes ha"' of the Indian white shrimp Penaeus indicus at 20 g size may be obtained in these ponds. P. indicus was isolated from local stocks (Gizan) and has now been cultured through several generations at the Fish Farming Centre. Present work has determined that the optimal salinity for larval culture is 30960 and for nursery culture 25-30960. The best stage for transfer from nursery to growout pond (43960) is about PL25. Comparison with biological data for P. indicus cultured elsewhere indicates that Red Sea populations may be preadapted to tolerate high salinities. The potential for artificial feeds to replace live feeds in P. indicus larval culture from Z1 to PL1 and PL5 using microencapsulated feeds, Nippai and Frippak has been investigated. Results reveal that 50% replacement with Nippai and Frippak is possible giving comparable growth to the control, but poorer survival. Also comparative growth trials were conducted with post larval P. indicus (PL5-PL30) spawned from Red Sea stock and cultured through larval stages on five feeds (Chaetoceros, Tetraselmis and Artemia). Post larvae were reared on commercial feeds: Taiwanese, Nippai, Frippak and 4 formulated feeds based on locally available ingredients at 28-30°C and at 3016 and 42i salinities. Feeding trials at 42% produced poor survival, but at 30% all treatments gave over 50% survival to PL25, at which stage shrimp are ready for stocking in growout ponds. Although the Taiwanese feed produced the overall fastest growth, it was not significantly better (P > 0.05) than two locally formulated diets (FFC1,4) or Frippak. Survival rates of over 60% where achieved on all diets with the exception of Nippai and Taiwanese feeds. Yields were significantly higher (P < 0.05) on one of the locally prepared diets (FFC1) than Taiwanese and Nippai, and Taiwanese than Nippai. All diets yielded significantly more shrimp biomass at 30960 than 4216 (P > 0.05). The relative costs of imported and locally produced diets are discussed and it is concluded that it is possible to produce cost-effective nursery diets in Saudi Arabia. A growout feeding study for P. indicus juvenile utilising 4 locally formulated diets compared with a Taiwanese diet revealed no significant difference (P. > 0.05) in survival nor in growth or yield amongst all diets. However growth was slow due to low pH and high ammonia levels. Finally shrimp density production trials at 20, 40,60 and 80m"2 during winter and summer were conducted in cages placed in a rubber lined pond. For all densities; yields were significantly higher in summer than winter with an overall average of 3.41±1.5 tonnes and 4.04±2.36 tonnes 180 days-- for winter and summer respectively. Yield at 80m'1 was highest but was not different from yield at 60m'2. Based on average harvested size and market price the density of 60. =was regarded suitable for growout culture.