Lake Victoria is African's most important source of inland fishery production, exhibiting an annual catch of ≈500 000 mt. The lake moderates local climate, serves as a means of transport, and a source of human food and raw material for the fishmeal industry. The introduction of Nile perch transformed the fisheries from a locally based artisanal fishery to a national and international capital investment industry. The fisheries produce an annual income of $US 600 million, providing employment opportunities for over 3 million people. Although the benefits of transforming the fishery of Lake Victoria appear to be quite remarkable, the negative impacts of this development are even more dramatic.Several challenges face the lake fishery, including environmental degradation, the introduction of exotic species, overfishing, and a fish export ban. Nutrients inputs into the lake have resulted in eutrophication and increased algal blooms. Deteriorated water quality and increased anoxia have caused the displacement and decline of some fish species. Exotic tilapiines have hybridized, displacing the indigenous fish species. Nile perch predation has caused the disappearance of once abundant native fish species. The once complex food web is now dominated by Nile perch. Unhygienic fishing methods have led to several fish export bans, while water hyacinth invasion in the lake has affected water quality, fishing and transportation possibilities. The current top-down management and use of different regulations by the riparian states have been a major drawback to sustainable management of the lake. There is a need for a paradigm shift, in which the lake is considered to be one ecosystem and relevant stakeholders are involved in the decision-making process.

We investigated effects of dietary administration of stinging nettle (Urtica dioica) on growth performance, biochemical, hematological and immunological parameters in juvenile and adult Victoria Labeo (Labeo victorianus) against Aeromonas hydrophila. Fish were divided into 4 groups and fed for 4 and 16 weeks with 0%, 1%, 2% and 5% of U. dioica incorporated into the diet. Use of U. dioica in the diet resulted in improved biochemical, hematological and immunological parameters. Among the biochemical parameters; plasma cortisol, glucose, triglyceride and cholesterol decreased while total protein and albumin in fish increased with increasing dietary inclusion of U. dioica. Among the haematology parameters: red blood cell (RBC), white blood cell (WBC) counts, haematocrit (Htc), mean cell haemoglobin (MCH), mean cell haemoglobin concentration (MCHC) and netrophiles increased with increasing dietary inclusion levels of U. dioica, some depending on the fish age. Serum immunoglobulins, lysozyme activity and respiratory burst were the main immunological parameters in the adult and juvenile L. victorianus measured and they all increased with increasing herbal inclusion of U. dioica in the diet. Dietary incorporation of U. dioica at 5% showed significantly higher relative percentage survival (up to 95%) against A. hydrophila. The current results demonstrate that using U. dioica can stimulate fish immunity and make L. victorianus more resistant to bacterial infection (A. hydrophila).

Essential oils (EOs) are used in the food industry because of their biological activity. We evaluated the effects of administration of essential oil (EO) extracted from bitter lemon (Citrus limon) fruit peels on the growth performance, biochemical, haemato‐immunological parameters and possible disease resistance in fingerlings (4 weeks old) Labeo victorianus challenged with Aeromonas hydrophila. Fish were divided into five groups and fed diets supplemented with C. limon fruit peels EO extract at 1%, 2%, 5% and 8% [as fed basis] and treatment compared with control group fed diet without C. limon fruit peels EO extract. The experiment was executed in triplicate. Concentration of plasma cortisol, glucose, triglyceride and cholesterol decreased while that of total protein and albumin increased as dietary inclusion of the EO extract of C. limon fruit peels was increased from 2% to 5%. Meanwhile haemato‐immunological parameters including red blood cell (RBC), white blood cell (WBC) counts, haematocrit (Htc), mean cell haemoglobin (MCH), mean cell haemoglobin concentration (MCHC) and neutrophiles increased with increasing dietary inclusion from 1% to 5% inclusion of C. limon fruit peels EO extract. Serum immunoglobulins, lysozyme activity and respiratory burst increased with increasing dietary levels up to 5% inclusion of EO extract of C. limon fruit peels. We demonstrate that formulation of feeds by incorporating upto 5% the EO extract from C. limon fruit peels significantly improved biochemical, haematological and immunological response in juvenile fish resulting to lower mortality than the untreated groups and appear to be effective antibacterial against A. hydrophila.

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