Abstract. This study was designed to evaluate morphological differences between cultured and wild African catfish, Clarias gariepinus (Burchell). Fish samples were collected from the lower Benue River (axis in Makurdi), while cultured fish were obtained from the University of Agriculture Makurdi research farm. The results revealed significant sex-related variation in the fish from different environments. Significant differences were observed in all morphometric parameters measured and in three of the five meristic counts recorded. Discriminant analysis and cluster analysis of morphometric parameters showed a high divergence among the populations, hence the tested fish samples were grouped into respective environments by sex. The meristic count, however, overlapped broadly showing no divergence among the populations. The morphometric differences between the cultured and wild African catfish could have been linked to genetic differences or environmental factors or a combination of both factors.

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A total of one hundred and twenty Clarias gariepinus comprising 30 dead and 30 live fishes were examined for protozoan parasites infestation, sixty each from the wild and a pond (cultured environment) over a period of six months. Ichthyophthirius multifiliis was the most common protozoan parasites found in C. gariepinus from the wild (River Benue) and cultured (pond) environments. These protozoan parasites constitute 37.08% of the total parasites encountered for fishes in the pond and 42.51% of fishes in the wild. Among the body parts of the sampled fishes from the pond, the gills had the highest parasite load (38.86%). Also, the gills had the highest parasite load (40.54%) among the body parts of the fishes sampled from the wild. Fishes not infested with any protozoan parasites from the pond constituted 36.70% of the total fish sampled. On the other hand, fishes not infested with any protozoan parasites from the wild constituted 31.65% of the total fish sampled. Female fishes had more protozoan parasites than the male fishes. Bigger fishes of total length (25–48 cm) had more parasite load than the smaller ones (19–24 cm). Also, fishes between 150–750 g had more parasite load than the smaller ones of less than 150 g. Protozoan parasite load of fish from the cultured environment (pond) did not differ significantly (P < 0.05) from those from River Benue (wild).

This research investigated the use of pawpaw Carica papaya seed meal (PSM) as a natural sex-reversal agent in tilapia production and its effect on growth. Freshly hatched fry of Nile Tilapia Oreochromis niloticus were collected from brooders and randomly distributed (n = 50) to 15 aquarium tanks (30 × 30 × 20 cm 3 ). They were fed a commercial diet (35% crude protein) blended with varying levels of PSM (0, 2, 4, 6, and 8 g/kg) for 28 d. Fingerlings were then maintained in outdoor concrete tanks (1 × 1 × 1 m 3 ) and were fed the commercial diet (without the inclusion of PSM) for 140 d. Growth evaluation and sexual phenotype of the fish were recorded during the treatment and recovery periods. The results obtained showed that growth of treated fish was significantly reduced compared to the control group during the treatment period; however, the trend reversed during the recovery period. The optimal PSM inclusion that gave the maximum weight gain (32.65 g) and masculinization percentage (82.19%) was 4.27 g/kg. The female phenotype was not noticed in treatments with inclusion levels greater than 2 g/kg; hence, reproduction was effectively controlled in the treated groups. However, percentages of fish with modified or reduced gonads significantly increased at 4-g/kg and greater PSM inclusion levels. Due to the biodegradable nature of PSM, it could be used as a viable alternative to popular synthetic hormones.

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