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).

Rotifers dominate zooplankton biomass of many aquatic environments. However, their link to food web biomass has rarely been elucidated in alkaline-saline lakes. Variations in C content, C:N ratio and stable isotope composition (d 13 C, d 15 N) of dominant rotifer species were studied from January to December 2008 in alkaline-saline Lake Nakuru to provide insights into their bioenergetics. We established that Brachionus dimidiatus dominated in terms of abundance (80,000-100,000 9 10 3 ind m -3 ) and C-biomass. Also B. dimidiatus constituted about 60-75% of the rotifer biomass in the samples. All the rotifer species exhibited significant (P \ 0.05) seasonal differences in biomass, C and C:N ratios. Rotifers had lower mean d 13 C than course particulate organic matter, fine particulate organic matter and fish, but higher than mean d 13 C in the dominant phytoplankton species. In all species, d 13 C and d 15 N increased markedly during the rainy season reflecting the feeding onset on allochthonous food sources. The isotopic increase correlated with an increase in their C:N. Our results demonstrate that rotifers respond quickly to any increase in primary production and can cope with changes in its nature and timing.