Sexual condition of female Hilsa was sampled from October 1983 to August 1984 from freshwater, estuarine and marine localities in Bangladesh. At Chandpur, on the River Meghna, changes in gonadosomatic index showed that early monsoon (June), late monsoon (October), and winter (February) are the major spawning periods. Ages of juvenile Hilsa were determined up to six months old (12 cm long) by counting daily growth rings of otoliths. Hatching dates of juveniles collected in different months were back calculated from otolith readings, and confirmed the existence of the three spawning peaks. Migratory movements of juvenile Hilsa in the River Meghna were studied from samples obtained by experimental beach seining, by experimental drift gill netting, and by fishermen's gear. Length-frequency analysis of fish from beach seines and from fishermen's catch indicated juveniles less than 8 cm in total length inhabit shore and shallow river areas (<10 ft depth). When juveniles attain a larger size (>7 cm) they migrate to the deeper river (>10 ft depth) in January. After reaching 12 cm, all disappeared from the deeper river in May. Their migration from the river towards the sea was indicated by the direction of gilling in experimental nets, and by mean length analysis of juveniles collected in the upper and downstream areas of the River Meghna. / Science, Faculty of / Zoology, Department of / Graduate

Data were gathered in 1983 and 1984 on the Hilsa fishery in the Meghna River in Bangladesh, and on factors related to its seasonal variation, including effort as estimated by weekly counts of fishing boats, and landings as estimated by counts of fish offloaded at Chandpur. Historical data were also analyzed concerning factors influencing annual variations in Hilsa landings from the Padma River of the Ganges (1967-1974) and from the Indus River of Pakistan (1968-1982). Rail shipments were good indicators of landings. No significant relationship was observed between riverine Hilsa landings and fishing intensity. Rainfall, mean water level and maximum air temperature had no obvious influence on annual variations in seasonal timing of Hilsa runs in the Padma river of the Ganges. Rainfall two years earlier had a significant negative relationship with annual variation of Hilsa landings, in both the Padma River and in the Indus River. Mechanisms regulating this negative association between landings and rainfall may be that Hilsa are 1+ year old when they are first recruited to the fishery, and the survival of eggs and fry is minimum in years when there is a very high rainfall. In the Ganges and Indus rivers, annual landings were not closely correlated, and appear to be dependent in part on earlier rainfall conditions within each region. This dependency offers a means of rough forecast of annual harvest on the basis of previous rainfall data. / Science, Faculty of / Zoology, Department of / Graduate