OBSERVATIONS ON CERTAIN ASPECTS OF THE BIOLOGY OF METAPENAEUS BREVICORNIS (H. MILNE-EDWARDS) AND PENAEUS MERGUIENSIS DE MAN IN THE BRUNEI ESTUARINE SYSTEM

Abstract

The aspects of the biology of two commercially important species of penaeid prawns, Metapenaeus brevicornis and Penaeus merguiensis, which have been studied for the first time in the present investigation include certain aspects of their ecology in the Brunei estuarine system, the length-weight relationship, the spawning seasons, the breeding behaviour and the larval development. The hydrological aspects of the Brunei estuarine system studied include observations on pH, rainfall, water temperature, salinity and dissolved inorganic phosphate. The inverse relationship between rainfall and salinity was found to be statistically significant. The vertical distribution of salinity follows the pattern for estuarine systems in other parts of this region. As a result of heavy land drainage, the dissolved phosphate content was found to very high as in other estuarine systems. The reproductive behaviour and all the larval and post-larval stages of these two species were observed and recorded for the first time, This has been made possible because fertilized females of both species were procured from the sea and kept in large sea water aquaria where they spawned and the larval stages developed, It was found that spent females of these two species were numerous in the sea catches of prawns during the months of high salinities and low rainfall, indicating that spawning occurred in the sea during these periods. In the aquaria spawning occurred early in the morning from 4 a.m. to 6 a.m. Segmentation of the fertilised eggs was holoblastic. There was a characteristic rotation of the two daughter cells resulting from the first cleavage. The nauplii hatched out in about 11 to 12 hours after spawning. In Metapenaeus brevicornis 6 naupliar, 3 protozoeal, 3 mysis and 12 postlarval stages were observed and drawn. In Penaeus merguiensis 6 naupliar, 3 protozoeal, 3 mysis and 15 postlarval stages were observed and drawn. The feeding behaviour and mortality of the larval stages were also studied. The possibility of cultivating these two species was discussed.