Experimental studies on acclimatization of marine shrimps, Penaeus monodon and Metapenaeus monoceros to freshwaterThe adult shrimps, Penaeus monodon and Metapenaeus monoceros were induced to mature and spawn by eyestalk ablation. The larvae of both the species of shrimps were reared up to post larval stage on a diet of the phytoplankton, Chaetoceros calcitrans. The post larvae of M. monoceros were fed with artificial feeds only, whereas the post larvae of P. monodon were fed on small quantities of Artemia sp. in addition to artificial feed. After post larval stage, PL-20, the post-larvae were acclimatized to freshwater. Acclimatization was tried for different periods ranging between 2 and 20 days. The best survival rate was obtained for an acclimatization period of 5 days. Results obtained so far showed that the growth of P. monodon was significantly higher in freshwater. The methodologies of larval rearing, acclimatization and the results obtained on the growth of P. monodon in freshwater and seawater are described.
Larval rearing techniques and stock enhancement of silver seabream (Rhabdosargus sarba) in MauritiusThe silver sea bream (Rhabdosargus sarba), has great commercial value in Mauritius. The species is a potential candidate for aquaculture. The sea bream, a winter spawner, was successfully induced to breed in captivity with HCG (Human Chorionic Gonadotropin) hormone injection (250 IU/kg body weight) in 1989 at the Albion Fisheries Research Centre. In 1997, the Coastal Fisheries Resources and Environment Conservation Project of Japanese International Cooperation Agency (JICA) was launched to enhance the stock of the silver sea bream in the lagoon. This species breeds under hatchery conditions during the spawning season. Annually, the hatchery-produced sea bream fingerlings, of 2.0 to 2.5 cm body length, were released in the coastal areas. The larval rearing method adopted at the Albion Fisheries Research Centre is described.
Some results of the study on rearing of mangrove crab Scylla serrata juveniles in the barachois of MauritiusThe mangrove crab, Scylla serrata (Forskal) is a potential candidate for aquaculture development in Mauritius and experimental trials on its culture were carried out from 1997 to 2002. It has a fast growth rate and tolerates a wide range of physico-chemical parameters. The survival rate of Scylla serrata, both under the controlled/hatchery conditions and in the natural eco-habitat is low. In 1997, the Japan International Cooperation Agency (JICA) launched the “Coastal Fisheries Resources & Environment Conservation Project” to enhance the stock of crab in the lagoon waters. The quantity of crab juveniles for culture in barachois is dependent on the availability of seed in the lagoon. Hatchery-produced crab juveniles were reared for experimentation/study in pen enclosures in two barachois prior to release in the coastal areas. The bio-indicators, stocking density and feeding regime differed in the two experimental studies. These experiments indicated varying survival and growth rates using different feeding regimes and stocking densities.
Analysis of Tag Recoveries in Mauritius (1988-1993) and Presentation of Codification Procedure in UseTagging is considered an excellent tool for estimating the importance of interactions and competition between fisheries as well as to study tuna stocks and migrations. The Regional Tuna Project of the Indian Ocean Commission (IOC) conducted five tagging cruises in the western Indian Ocean, during which 955 fishes were tagged. Out of the total number tagged 15 were recaptured. Tuna tagging in the Indian Ocean was also undertaken by the Indo- Pacific Tuna Programme and by the Japanese National Research Institute of Far Seas Fisheries. 39 tuna marked by these organisations were recovered in Mauritius. Analysis of data collected from the tag recoveries provide some preliminary estimates of growth rate and migration of tuna. Tagging is the most direct method to estimate growth, stock structure, schooling behaviour and migrations; it also provides essential information for estimating mortality (natural and fishing) and fisheries interactions and thus is pertinent for defining proper management of a stock.