地理ジャーナルと自然災害
オープンアクセス

概要

Ovarian Development of the Penaeid Shrimp Penaeus indicus (Decapoda): A Case for the Indian Ocean Coastal Waters of Kilifi Creek, Kenya

Chadwick Bironga Henry, Christopher Aura Mulanda and James Njiru

The Indian prawn Penaeus indicus, is one of the major commercial shrimp species globally. It is widely distributed in the Indo-West Pacific; from eastern and south-eastern Africa, through India, Malaysia and Indonesia to southern China and northern Australia. The species has been recorded to reach 22 cm, inhabiting depths of 100 m. Globally P. indicus is widely studied, although majority of the studies have focused on developmental stages between shallow waters and the deep seas. Studies indicate that development takes place in the sea before the larvae move into estuaries to grow, then return as sub-adults. However, studies on the maturity of this species in shallow waters and especially creeks and embayments are clearly lacking for the Kenyan coastline. This study was conducted in the Kilifi Creek, north coast Kenya, from the mouth at the Kilifi Bridge to past Kibokoni, some 5 km into the creek. Samples were collected from 6 landing sites. Morphometric and biological data including total length (TL, cm), carapace length (CL, cm), body weight (BW, g) and sex were recorded, and the specimens dissected to check for ovarian development and maturity. Ovarian development stages were determined from size, shape and colour of the ovaries, and through frequency analysis of the cortical granules. A total of 1,149 specimens were sampled from January to April, 2018. The catch mostly comprised of the 1.5 cm to 2.5 cm CL size class. However some individuals in the >4.0 cm CL size class were also recorded suggesting that some individuals still matured in the creeks although majority are known to migrate deep sea. Regression analysis showed a strong positive correlation between CL, and TL (r²=0.7548) and BW (r²=0.7497). The condition factor ranged from 0.19-0.94 indicating presence of both immature/spent (4.7%) and ripe individuals (95.3%) in good condition. Size frequency analysis of the ovary cortical granules displayed a poly-modal pattern with 2 peaks of immaturity and 3 peaks for developing and near-ripe respectively. The presence of spent stages as well as mature specimens in the creek waters indicated that apart from using these habitats as nursery and feeding grounds, some of the individuals might also be growing, maturing and spawning in the creek, calling for further studies into the assessment of the growth patterns and reproductive aspects of this species in the Kilifi Creek and other coastal waters.