Ethmalosa Research Articles

Trophic ecology and ecomorphology of fish assemblages in coastal lakes of Benin, West Africa

:The feeding ecology and morphological diversification of fish assemblages of two coastal lakes in southern Benin (West Africa) were examined to compare patterns of community organization. Though located only 18 km apart, the two fish assemblages had dissimilar species composition, and this is largely derived from differences in connectivity to the Gulf of Guinea, salinity and pH. Among the 35 and 20 species sampled from Lake Nokoue (connected with a sea) and Lagoon Toho-Todougba (no sea connection), respectively, only a few species dominated each system. Lake Nokoue was dominated by the perciform Gerres melanopterus and the clupeiform Ethmalosa fimbriata, and Lagoon Toho-Todougba was dominated by the characiform Brycinus longipinnis. In Lake Nokoue, the akadja habitat (dense stands of woody debris installed by humans to attract fishes) had high species richness compared to the other lake habitats. Multivariate procedures were used to examine trophic guilds and the relationship between morphology and diet. Overall, thirteen trophic guilds were identified, with detritivore and piscivore guilds having the most species. Lagoon Toho-Todougba was dominated by detritivorous and insectivorous species and Lake Nokoue, a larger lake with a connection to the sea, was dominated by piscivores. In Lagoon Toho-Todougba, consumption of vegetation and insects was common, but these items were very rare in Lake Nokoue fish diets, possibly because the destruction of its fringing mangroves has reduced their availability for fishes. Despite major differences in taxonomic composition, the two fish assemblages had similar mean values for most morphological traits and morphological-based centroids from multivariate analyses were remarkably similar. Because members of the same feeding guild tended to have similar morphologies, some degree of diet specialization has accompanied morphological diversification in the taxa comprising these communities.

Studies on species of fungi associated with mycotic infections of fish in a Nigerian freshwater fish pond

A survey was carried out on the species of fungi associated with mycotic infections of fish in a Nigerian freshwater fish pond. A total of 24 fungal species belonging to 6 genera of aquatic phycomycete were isolated from the infected fishes. Achlya racemosa, Aphanomyces laevis, Dictyuchus sterile, Saprolegnia ferax, S. litoralis and S. parasitica had 100% frequency of occurrence amongst the infected fishes. There were similarities in the species of fungi isolated from the infected fishes in the fish pond and those isolated from the hatchery. Of the infected fishes, Clarias lazera had the highest number of fungal isolates. It was followed by Tilapia zilli, then by Chanos chanos, Ethmalosa fimbriata and finally by Cyprinus carpio. The implications of the results obtained on the development of fish farming in Nigeria are discussed.

The seasonal occurrence and bionomics of the bonga, Ethmalosa fimbriata (Bowdich) off Aiyetoro Coast, Nigeria

The monthly occurrence of the bonga, Ethmalosa fimbriata (Bowdich) in a trawl catch off Aiyetoro Coast, Nigeria was monitored over a 2-year period. The adult fish were abundant in the catch during the dry months of December–May and in June immediately before the onset of the rainy season. The peak of occurrence was in the month of April of both years. Aspects of the biology of the bonga were also examined with particular reference to the size distribution, food organisms and fecundity.

Growth, mortality and potential yield of bonga, Ethmalosa fimbriata (Bowdich 1825) of Nigerian inshore waters

The distribution of and fisheries for bonga, Ethmalosa fimbriata (Clupeidae), in Nigerian inshore waters east of the Niger delta are discussed. Data on length frequency collected between 1973 and 1982 are analysed to obtain the von Bertalanffy's growth parameters ( L ∞=30 cm, K=0.43 and T 0=−0.20) which are then used to estimate the instantaneous total ( Z), natural ( M) and fishing ( F) mortality coefficients. Catch-per-effort statistics (1973–1982) allow for a simple graphical treatment of Schaefer's logistic model from which the maximum sustainable yield ( Y max=30 075 t year −1) is derived for the stock of bonga in this part of the Nigerian coast. Considering the level of mean catch (25 030 t year −1), which is very close to the optimum level of yield ( Y ec) and the mean value of the exploitation ratio ( F Z =0.57 ), it is concluded that the stock of E. fimbriata of the inshore waters east of the Niger delta is being fished at about its Y ec. Although this is the desirable level of exploitation if profit is to be maximized, this fishery might be allowed to expand beyond Y ec to contribute to the solution of an important socio-economic problem, namely, reduction of unemployment, but fishing at Y max should be avoided to prevent the collapse of the stock.

Benthic-pelagic coupling and export of organic carbon from a tropical Atlantic continental shelf—Sierra Leone

An approximate carbon budget for the Sierra Leone River Estuary and adjacent inner continental shelf indicates that phytoplankton production is balanced by grazers only in the wet season estuary; on the continental shelf, and in the dry season estuary, phytoplankton production exceeds demand of consumer populations by 70–90%. Regional production is dominated by the dry season estuary where diatom blooms support large population of the phytophagous clupeid fish Ethmalosa fimbriata. It is suggested that as well as what is used in bacterial respiration, not quantified in the study, important amounts of inshore organic carbon production are available for export, or burial, or both, either in inshore mudbanks or at the shelf edge by slumping. This carbon budget for a tropical continental shelf having neither coral-reefs nor coastal upwelling appears to correspond with what is emerging as a generic distinction between shelves and open ocean ecosystems: surplus production on shelves, balance between producers and consumers in the open ocean.

Observations on the reproductive biology of the shad, Ethmalosa fimbriata (Bowdich), in the coastal waters of Cape Coast, Ghana

The gonads of Ethmalosa fimbriata have been classified according to five and four maturity stages in the male and female, respectively. The species appears to mature at 22.0 cm in Ghana waters. The fecundity and frequency distribution of oocytes have been determined. Monthly changes in the proportions of gonadal stages and gonadosomatic index indicate that the species spawns in the sea from October to March. The results have been compared with data on populations occurring in other West African countries.

Feeding activity and food habits of the shad, Ethmalosa fimbriata (Bowdich), in the coastal waters of Cape Coast, Ghana

The monthly feeding activity and food habits of populations of Ethmalosa fimbriata occurring in the sea and an estuary in Cape Coast, Ghana district were investigated during a 14‐month period. The juvenile fish, whose total length (T.L.) ranged from 5.3 to 14.7 cm, occur in the estuary and appeared to be more active feeders than the marine samples which measured 15.0–30.4 cm. The peak feeding activity in the marine population coincided with the onset of‘upwelling’ in the sea, which period is characterized by high salinities, decreasing temperatures and high zooplankton production. The species is primarily a plankton feeder. The stomachs of the marine samples contained mainly protozoa, crustacea, molluscan larvae and a considerable amount of detritus while the stomachs of the estuarine fish contained mainly phytoplankton, protozoa, sand grains and organic detritus. These observations have been discussed in relation to other reports on populations occurring along the West African coast.

The biology of the West African shad Ethmalosa fimbriata (Bowdich) in the Lagos Lagoon, Nigeria

The biology of the population of Ethmalosa fimbriata occurring in the Lagos lagoon was investigated. Three size groups, 35–69 mm (Yoyo), 70–169 mm (Efolo) and 170 mm and above (Agbodo) occur in the lagoon and the spatial distribution of these size groups and the length frequency distribution of the species is given. The relationship between length, weight, age and growth is discussed and the food and feeding intra‐relationship of the size groups is shown. Information on the fecundity and possible spawning periods is discussed.