The distribution of non-essential trace elements in some vital organs of 11 fish species from Aiba Reservoir, Iwo, Nigeria was assessed between November 2010 and June 2011. The fish species belong to seven families; family Mormyridae, family Cyprinidae, family Hepsetidae and family Channidae each with one species; family Bagridae and family Clariidae each with two species; and family Cichlidae with three species. All families, except Clariidae and Channidae, are common in the daily catch from the reservoir. Atomic absorption spectrophotometry was used to determine the levels of cadmium, mercury and lead in fish organs. The concentration of toxic trace metals in fish ranged from 0.001 to 0.100 ppm (Cd), 0.000–0.067 ppm (Hg) and 0.001–0.125 ppm (Pb) dry weight. This study shows similarity (p > 0.05) in the distribution of Cd, Hg and Pb among fish species; and a non-uniform distribution of toxic trace metals within fish organs with Kidney > Liver > Gill ≥ Intestine ≥ Muscle. Canonical variate analysis shows clear discrimination of Clarias macromystax and Channa obscura for gill trace metal levels of Cd, Hg and Pb while Labeo senegalensis and Oreochromis niloticus were discriminated for liver trace metal values of Cd and Pb only when compared to other fish species studied. The discrimination of some fish species based on trace metals in the gills and liver suggests different regulatory strategies for trace metal accumulation. Variation due to comparison among different fish species from the same water body suggests that accumulation may be species dependent. Differential accumulation of toxic trace metals in fish organs makes them good bioindicators of freshwater contamination.

Chrysichthys nigrodigitatus and C. auratus are important, highly valued and threatened freshwater species. To contribute with their ecological knowledge, the condition factor and diet of these two congeneric species were studied between April 2005 and April 2006. Food items of fish were evaluated by occurrence and numerical abundance methods, and the possible changes among sexes, seasons and sizes were considered. Results showed that generally C. nigrodigitatus were better conditioned than C. auratus. The males of C. nigrodigitatus and females of C. auratus were in better condition than their respective opposite sex throughout the year, and during the wet season compared to the dry. The food items of C. nigrodigitatus and C. auratus were similar and comprised twelve species belonging to five groups: Insecta (three species), Crustacea (five species), Arachnida (one species), Rotifera (one species) and Mollusca (two species). Other food items included fish scales, unidentified green eggs, plant parts, detritus and sand. Insecta and Crustacea dominated the food items in both species. For C. nigrodigitatus, insect consumption increased with fish size, while Crustacea items decreased (from 89.59% for 8.1cm-12.0cm size class to 1.58% for 20.1cm-26.0cm size class). However, while C. auratus smaller sized fish preferred Crustacea (98.72% for 8.1cm-12.0cm size class), larger sized fish had both groups in relatively similar amounts. Schoener Overlap Index for both species and between seasons is 1.00. Diet breadth ranged from 0.00-1.47 for C. nigrodigitatus and 0.00-1.32 for C. auratus. Food Richness ranged from 0.00-1.44 for both species. Gut Repletion Index for C. nigrodigitatus and C. auratus are 76.39% and 76.27% respectively. Although, there is considerable similarity and overlap in the utilization of food resource for both coexisting species, condition factor and feeding behavior suggest strategies to reduce intra-and interspecific competition.

The quest for renewable energy generation is fast increasing globally due to environmental degradation by fossil fuels. The energy production from the anaerobic codigestion of pineapple peels (PPs) and poultry manure (PM) was assessed in the present study. Prior to digestion, the PPs were pretreated using a strong acid (sulfuric acid) and a low-cost mild alkali hydrogen peroxide (H 2 O 2 ) which was prepared via the adjustment of the pH of H 2 O 2 to 11.5 by adding solution of 5 M NaOH. The physicochemical and structural parameters of the biomass, as well as microbial composition, were evaluated by using standard methodologies, while all structural changes to the biomass after pretreatment were determined using the Fourier transform infrared spectra. The application of alkaline H 2 O 2 pretreatment removed 71.34% of lignin, reduced hemicellulose by 61%, but increased the cellulose content by 39%. The alkaline pretreated pineapple peel (Al-P PP) was able to produce about 91% more biogas than the acid pretreated pineapple peel (Ac-P PP) and 36% more than the two untreated biomass samples. The results of the economic assessment of pretreatment also showed that investment into the use of H 2 O 2 for pretreatment is economically feasible with high net thermal and electrical energy gain, while that of acid pretreatment results in loses. Therefore, alkaline pretreatment application to PPs prior to digestion is hereby solicited in the biotechnological conversion of PPs/wastes for biogas and quality digestate which can be used as biofertilizers or soil enhancers especially in those regions where pineapple production is enormous.

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