|Keywords (Extracted from title, table of contents and abstract of thesis)
shrimps, penaeids, penaeus penicillatus, p.merguiensis, p. indicus, p. semisulcatus, metapenaeus affinis, m. monoceros, m. brevicornis, m. stebbingi, parapenaeopsis stylifera, p. hardwickii, p. sculptilis, parapenaeus longipes, metapenaeopsis stridulans
The shrimp landings at the Karachi fish Harbour were found to be comprised of 13-species of penaeids. These were: Penaeus penicillatus, P.merguiensis, P. indicus, P. semisulcatus, Metapenaeus affinis, M. monoceros, M. brevicornis, M. stebbingi, Parapenaeopsis stylifera, P. hardwickii, P. sculptilis, Parapenaeus longipes and Metapenaeopsis stridulans. These shrmps are sorted by fishermen on board, subsequently marketing them as Jaira (Penaeus species), Kalri (Metapenaeus species) and Kiddi (Parapenaeopsis species) group of shrimps at the Karachi fish Harbour. The The jaira group of shrimps were found to be mostly comprised of P. penicillatus and P. merguiensis. The principal species comprising the Kalri and Kiddi shrimps were respectively, M. affiants and P.stylifera.
The study of the minimum and maximum sizes of important Jaira, Kalri and Kiddi shrimp species and their size frequencies revealed the fact that shrimp size in the present day penaeid stocks of Pakistan is smaller than it was more than twenty years ago, providing unequivocal evidence of much continuous over fishing of these stocks.
The females of the four main commercially important penaeid shrimps, P. penicillatus, P. merguiensis, M. affinis and P. stylifera were found to attain a size larger than their males. This suggests the possibility that males die off earlier than females or that females grow faster in the later part of their life and live longer than males. The possibility that in these species sex-reversal occurs from males to females cannot be ruled out also. The overall sex-rations in P. penicillatus, P. merguiensis and M. affinis did not deviate from the expected 1:1 or normal Medelian distribution. However, in P. stylifera the overall sex-ratio deviated significantly from the expected 1:1 distributions in favour of females, being 3:1.
In this study, six maturation stages were recognized on the basis of overian histology. These were undeveloped, developing, nearly-ripe, fully-ripe, resorbing and resorbing/developing. The spewning seasons of local penaeid shrimps, P. penicillatus, P. merguiensis, M. affinis, and P. stylifera based on the maturation stages of the overies revealed that all the four species had nearly-ripe or fully-ripe overies throughout the year suggesting the potential for spewning throughout the year. Penaeus penicillatus, P. merguiensis and M. affinis showed two peaks of spewning-the major peak in winter-spring and the minor peak in September/October. In P. stylifera the spewning is winter orented (Novermber to February). The recruits of both P. penicillatus and P. merguiensis belonged to the 101-120 mm size-class, of M. afinis to 81-100 mm size-class and of P. stylifera to 61-70 mm size-class. In P. penicillatus the recruitment occurred during the period September to December and in January to February, in M. affinis during September to December and May to June, while in P. stylifera the recruitment occurred almost throughout the year.