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Food and feeding habits of grey mullets (Mugilidae) in the River Volta and River Pra estuaries in Ghana were studied between February 1997 and July 1998 as part of efforts to encourage their culture. Stomach contents of fish samples, obtained with a cast net and a drag net, were analysed using the 'points' and frequency of occurrence method. Diatoms, detrital material and sand particles were the major items in the stomachs of all the species from the two estuaries. Their diet did not show any substantial seasonality, neither did it change with size. The various species ingested sand particles of selected range with Liza dumerilii ingesting the widest range in both estuaries, 41.2-1195.8 µm in the Volta estuary, and 33.0-1649.0 µm in the Pra estuary. Species that ingested the same modal size of sand particles showed preferences for different food items. The shortest mean relative gut length (gut length to body length ratio) of 1.82 and 1.72 were calculated for L. dumerilii in the Volta and Pra estuaries, respectively, while the longest mean relative gut length of 4.56 was calculated for Mugil cephalus in the Volta estuary and 4.33 for Liza grandisquamis in the Pra estuary. All the species showed a diurnal feeding habit, with the main feeding period occurring between 08.00 and 12.00 h. The peak feeding time, however, differed among the species.

Studies were carried out to determine the toxicity of some selected pesticides on fresh water fish in a tropical environment. The uptake of the pesticides lindane, pentachlorophenol (PCP), and propoxur, which are frequently used on farms, and in industries as well as by loggers and timber men on wood were studied in concrete ponds at the University of Cape Coast, in Ghana. The fish used for the study were Oreochromis niloticus, Clarias gariepinus, and Chrysicthys nigrodigitatus. They were obtained from cultured ponds in the Cape Coast and Mankessim districts in the Central Region and Weija Dam, in the Greater Accra region of Ghana. Single high lethal concentration (SD) or acute treatment and cumulative/chronic (or multiple minor) lethal concentration (CD) treatment were employed in administering the pesticides to the fish via water. Gas chromatograph electron capture detector analysis was done on the dead fish to see the extent of ingestion. The LC(50 )values obtained for lindane on the three fish samples were as follows: Chrysicthys - 0.38 mg L(-1); Oreochromis - 0.42 mg L(-1), and Clarias - 1.2 mg L(-1). Mortalities occurred in fish within 3-5 days of application. For the PCP on Chrysicthys, Oreochromis, and Clarias species the LC(50) values were 0.42, 0.32 and 0.64 mg L(-1), respectively, for over a 2- to 3-day period. For a three-time influx period of propoxur the LC(50) for Chrysicthys, Oreochromis, and Clarias, were 22.0, 30.40, and 45.04 (all in mg L(-1)), respectively. The results obtained indicated that the pesticides had adverse effects on the general growth and reproduction of fish as shown by gonadosomatic indices.

INTRODUCTIONYonge (1962) suggests a possible universal occurrence of byssal apparatus in the post-larval spat of bivalves. Subsequent studies have revealed that the byssus thread secreted by the post-larval byssal apparatus of many bivalves is involved in settlement as well as migration by means of bysso-pelagic drifting (Sigurdsson, Titman & Davis, 1976; Blok & Tan-Maas, 1977; Board, 1983). Recent studies on the byssus and other foot glands in the early stages of bivalves have included Ostrea edulis (Cranfield, 1973 a, b, c); Pecten maximus (Gruffydd, Lane & Beaumont, 1975); Mytilus edulis (Lane & Nott, 1975; Lane, Nott & Crisp, 1982); and Chlamys varia L. (Gruffydd, Budiman & Nott, 1979)