The reproductive biology of four African catfishes (Osteichthyes: Clariidae) in Anambra River basin,Nigeria

The reproductive biology of Clarias ebriensis, C. agboyiensis, C. macromystax and C. buthupogon was investigated over a period of 32 months in Anambra River basin, Nigeria. Immature (stage I) C. ebriensis and C. agboyiensis were recruited into the fishery in October, and in September in C. macromystax and C. buthupogon. The occurrence of mature (stage III) fish all the year round indicated the potential of the Clarias species to breed at any time of the year. C. ebriensis bred from April–September while breeding occurred from May–September in the other species. The clariids matured between their first and second year of life. C. ebriensis females matured earlier than males but the reserve was the case in C. agboyiensis, C. macromystax and C. buthupogon. Ovary weight was a better indicator of egg number than either total length or body weight in all species. Communal spawning is reported for the first time in Clarias species and its significance to survival discussed.     

The parasite fauna of characids' (Osteichthyes: Characidae) Anambra River, Nigeria

Baseline information on the parasites of frequently caught species of the characids namely Hydrocynus vittatus , Alestes baremoze , Brycinus macrolepidotus and Brycinus leuciscus was investigated in Anambra River from August 2004 to July 2005. The parasites recovered were the Myxosporid, Myxobolus sp (Protozoa), Polyopistocotylids, Diplozoon ghanense and Neodipolzoon polycotyleus (Monogeneans), the Caryophyllid Caryophylleus sp (Cestoda) and Rhabdochona sp (Nematoda). The prevalence of Caryophylleus sp in B. macrolepidotus (14.2%) and A. baremoze (8.1%) as well as Rhabdochon sp and Myxobolus sp in H . vittatus (9.6% and 7.8% respectively) was relatively high (>7.0%); while the other parasite species Myxobolus sp in B. leuciscus (2%), D. ghanense in B. macrolepidotus (1.9%) and N. polycotyleus in A. baremoze (1.9%) had a much lower prevalence (2.7%). Distribution of parasites was clearly seasonal. Dissolved oxygen (8.0–14.0) mg l⁻¹ and pH (5.5–7.0) influenced the occurrence of the parasites whereas temperature (20.1–27.5 DC) showed no much effect.     

The abundance and trophic biology of Clarias albopunctatus Nichols & LaMonte, 1953 (Osteichthyes: Clariidae) in a tropical floodriver basin

The abundance, food and feeding biology of Clarias albopunctatus was studied over a period of 17 months in the lower River Anambra, Nigeria. The catfish was more abundant in late dry season (January–March) and early rainy season (April–June) than in other periods of the year in the small-sized Akwu pond than in other habitats. Feeding intensity was higher at night and at dawn (20.00–05.00 h) than during the day (08.00–17.00 h) in the 151–200 mm TL size class and during the rainy season (April–September). There was no sex-dependent variation in feeding intensity. Insects were the predominant food, followed by crustaceans. Of primary importance were Chironomidae (mainly Chironomus spp. and Tanypus sp.), Odonata nymphs, Dytiscus sp., mosquito larvae and pupae, Gyrinus sp., Daphnia sp., Ostracoda and Tilapia fry. Qualitative food composition and food richness were size, but not sex – or season-dependent. Diet breadth increased with catfish size and during the rainy season. The feeding behaviour of the catfish include foraging, shovelling and surface feeding. Abundant food and ability to switch to more available items enable C. albopunctatus to maintain its abundance in the River Anambra. This revised version was published online in July 2006 with corrections to the Cover Date.