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The bioaccumulation and toxic effects of heavy metals have caused ecological damage to aquatic ecosystem. In this study, concentration of heavy metals including zinc, lead, cadmium, iron, and copper were determined in the sediment and water as well as in the muscle, gill, and intestine of two fish species (Pelmatochromis guentheri and Pelmatochromis pulcher) of Mbaa River in Southeastern Nigeria. Samples were collected at three different spots from the river, and the level of heavy metals specified above were determined by atomic absorption spectroscopy (AAS) after a modified wet digestion process. The results indicated that sediment had the highest concentration of the heavy metals investigated while water had the lowest concentration. Fish tissues showed appreciable bioaccumulation of these metals as evidenced by a higher concentration profile when compared with that of water. Furthermore, the concentration of these heavy metals in water and their bioconcentration factor in the fish were above the recommended limit by WHO and FEPA, indicating that Mbaa River along Inyishi may not be suitable for drinking nor the fish safe for human consumption. The study also reveals the use of fish as bioindicator of aquatic environment.

Jackbean (Canavalia ensiformis) is an under-utilised novel legume with crude protein content and amino acid profile that make it a potential candidate in the tropics as substitute for fish meal in fish diets. This study assesses the potentials of Jackbean seed meal (JBSM) for partial replacement of fish meal in diets of Clarias gariepinus. Fishmeal in control diet was replaced progressively (10%,20%,40% and 60%) by raw JBSM, 30-and 60-minute boiled JBSM. Test fish in each tank were fed 3% of their biomass twice daily for 56days. Fish fed control diet had the best SGR (1.61) and feed efficiencies (FCR 1.88, PER 1.74). SGR and PER of fish groups fed test diets were inversely related to the dietary levels of JBSM. The same trend applied to protein and fat contents of the fish carcass. FCR however had the reverse trend. Fish fed diets with up to 20% fishmeal substituted by 60 minute boiled JBSM had protein content similar to those fed the control diets (P<0.05). Fish fed diets with fishmeal substituted by 10% raw JBSM and up to 20% JBSM boiled for 30 and 60 minutes had similar fat levels in the fish flesh as those fed the controlled diets (P<0.05). The poor performance observed in fish fed diets containing increasing levels of boiled JBSM suggest the presence of probably thermostable antinutritional factors in processed JBSM as well as imbalance in the nutrient profile which may be corrected by supplementation. However, the study shows that 20% of fishmeal in the diet can be replaced with JBSM boiled for 60 minutes without any adverse effect on the growth performance.

No abstract

Raw undehulled pigeon pea, Cajanus cajan, seeds were processed by toasting, boiling, and soaking before milling to produce pigeon pea meals (PPMs). African catfish, Clarias gariepinus, were fed eight diets formulated with these meals at two dietary inclusion levels of 600 and 650  g/kg in combination with fish waste meal levels of 350 and 330 g/kg, respectively, to yield a protein and energy contents of 35.96  ±  2.1% dry matter and 18.04  ±  0.2 kJ/g. Fish (mean weight 0.46  g) were weighed and distributed to 24 experimental tanks (seven fish per tank). Triplicate fish groups were fed restricted ration (5% of biomass) per day in two portions for 56 d in static water. Results showed that fish groups fed raw PPM diets had low body weight gain (BWG), inferior specific growth rate (SGR), and high feed conversion ratio (FCR) when compared to other feeding groups. The hematocrit, hemoglobin concentration, and red blood cell and white blood cell counts decreased significantly (P  <  0.05) with raw PPM diets. Slight decrease also was recorded among groups fed diets of other processing methods when compared with initial fish. However, soaking for 16 h enhanced best fish BWG, SGR, FCR, and hematological values and can be recommended as a good processing method of PPM for African catfish diets.