The prevalence of fish parasites in Bagrus bayad and Protopterus annectens from Upper River Benue in Mutum Biu, Taraba State, Nigeria was carried out using standard parasitological method. The objectives of this study were to investigate the parasite species spectrum, prevalence of each parasites species, overall prevalence, prevalence of parasite infection in relation to the size and sexes of Bagrus bayad and Protopterus annectens and the infection induced by parasites on/in their body parts, with the view of providing relevant information that can be used in combating the rate of economic losses that could be experienced as a result of parasitic infestations. 4 parasite taxa comprising of Twelve (12) parasite species (Trichodina spp., Henneguya spp. Cryptobia iubilans, Diphillobothrium latum, Hymenolepis nanna and Bothriocephalus aengypticus, Capillaria philipinensis, Caenorhabditis briggsae, Camallanus spp., Eustrongylides spp., Contracaecum spp. and Clinostomum spp. were recovered from the samples of fish species used during the study period. Twelve (12) of the parasite species were recovered from Bagrus bayad while seven (7) were recovered from Protopterus annectens. Among the body parts of Bagrus bayad, while intestine had the highest percentage parasite load (56.37%), highest percentage parasite load (46.22%) in Protopterus annectens was recorded for stomach (46.22%). Out of the 400 fish samples comprising of 200 each of Bagrus bayad and Protopterus annectens, 234 (58.50%) comprising of 99 (49.50%) and 135 (67.50%) samples each of Bagrus bayad and Protopterus annectens were infested with 369 and 119 parasites, respectively. However, there was no significant difference in the prevalence of infection and parasite load between the fish species, respectively (P>0.05). Generally, larger sized samples of Bagrus bayad and Protopterus annectens had higher percentage of infection compared to the smaller sized of both samples although, the prevalence of infection in relation to sizes of both fish species was not statistically significant (P>0.05). Female Bagrus bayad and Protopterus annectens had higher prevalence of infection (21.61%) and (16.63%) than the males (6.37%) and (6.24%), respectively. There was no significant difference in the prevalence of infection in relation to the sexes of both fish species (P>0.05). Epidermal necrosis of the caudal fin and skin, thickened intestinal epithelium at the site of parasite attachment, hyperplasia of the intestinal villi and lamina propria, hyperplasia of infected gills at the secondary lamellae, ulceration of the stomach, abdominal distention, eroded and flattened intestinal folds and lymphocytic infiltration of intestinal mucosa and edema of the lamina propria of the intestine were observed with the infected samples of B. bayad. The infected samples of P. annectens exhibited epidermal necrosis of the skin.

Seasonal variation in parasitic prevalence of Oreochromis niloticus from Upper River Benue, Mutum Biu, Taraba State, Nigeria was conducted using standard parasitological methods. 400 samples of varied sizes of Oreochromis niloticus consisting of 200 samples each in dry and rainy seasons were bought from fishermen at the Upper River Benue, Mutum Biu, Taraba State for a period of ten months and transported fresh to the Parasitology Laboratory, College of Veterinary Medicine, Joseph Sarwuan Tarka University, Makurdi (formerly called University of Agriculture, Makurdi) where they were sorted out into different sizes and sexes. Out of the 400 samples comprising of 200 samples each of Oreochromis niloticus collected in dry and rainy seasons, 211 (52.75%) samples were infested with 605 parasites. Out of the 200 samples collected in dry season, while 105 (52.50%) were infested with 327 parasites, in rainy season, 106 (53.00%) samples were infested with 278 parasites out of the 200 samples. Prevalence of infection (53.00%) was higher in rainy season than dry season with prevalence of infection of 52.50% whereas, percentage parasite load (54.05%) was higher in dry season than rainy season with the percentage parasite load of 45.95%. Among the parasite species in dry season, while Camallanus spp. was the most prevalent (22.02%) Ichthyopthirius multifilis was the least (3.67%). In rainy season, while Diphillobothrium latum was the most prevalent (19.07%), Ichthyopthirius multifilis was the least (1.44%). Among the external parts, while the gill had the highest percentage parasite load in both seasons, the least was recorded for fin and skin, respectively. Percentage parasite load was higher in the intestine than the stomach in both seasons though, there was no significant difference (p>0.05) recorded for percentage parasite load of both external and internal parts of the fish samples in both seasons. Male Oreochromis niloticus had higher prevalence of infection and percentage parasite load than the female though, there was no significant difference (p>0.05) in the prevalence of infection and percentage parasite load and the sexes in both seasons. Samples of Oreochromis niloticus with longer lengths and greater weight had higher percentage parasite load than the samples with shorter lengths and smaller weight.