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Environmental enrichment (EE) improves the growth rate and welfare of some cultured fishes. However, most cultured fish species are raised in non-enriched housing conditions. Clarias gariepinus is an important commercial fish species, but little is known about the effect of EE on their welfare. This study examined the effect of different EE on the survival rate (SR), growth [mean weight gain (MWG), specific growth rate (SGR) and feed conversion ratio (FCR)], behavioral (feed response, aggressive acts and shoaling time) and physiological responses (blood glucose) of C. gariepinus. One hundred and twenty juveniles of C. gariepinus (31.65 ± 0.69 g) were randomly allocated at 10 fish/tank and subjected to either Plant Enriched (PE), Substratum Enriched (SE), Plant and Substratum Enriched (PSE) and Non-Enriched (NE) tanks in triplicates for 56-days. Behavioral acts were observed for 10 min twice daily, and glucose level in blood samples was evaluated. Data were checked for normality using the Shapiro-Wilk test before being analyzed with the Kruskal-Wallis test. SR and MWG were significantly higher in Clarias gariepinus exposed to SE, with no significant differences among PE, PSE and NE treatments. There was no significant difference between the SGR of PSE and NE. FCR was similar between treatments. The highest condition factor (k) was recorded in SE tanks. Duration of feed response was shorter in SE, but there was no significant difference between the feed response of C. gariepinus exposed to PE and PSE. C. gariepinus exposed to PE, SE and PSE displayed a similar frequency of aggressive acts. African catfish reared in NE (barren) tanks had the least duration of shoaling period. The experiment consistently found the highest and least glucose values in PSE and SE. In conclusion, environmentally enriched housing tanks with SE resulted in the best MWG with a reduced level of aggression in C. gariepinus under laboratory conditions. Thus, EE might be applicable to boost fish productivity on a commercial scale.

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The incidence of oil spills that finds their way into the aquatic environment constitutes a serious threat to the welfare of fish species and other aquatic biotas. However, the behavioural and stress response of C. gariepinus to paraffin oil (PO) has not been investigated under laboratory conditions to understand the welfare implication of this pollutant on fish species in petroleum polluted aquatic environments. Ninety-six juveniles of C. gariepinus were randomly allocated to 8fish/tank and subjected to four sub-lethal concentrations T1-0.4ml/L, T2-0.8ml/L, T3-1.6ml/L and T4-0.00 ml/L (control) of paraffin oil in triplicates. The fish were observed every 12-hours using the focal sampling technique for seven days. Behavioural traits observed were swimming (Non-active (NA), erratic (ER), Very-active (VA)), feeding (feed intake (FI), duration of feeding (DF)), aggressive (agonistic (AGO), number of bruises and scars (BS)) and respiratory (air gulping, (AG) mucus secretion (MS), Opercula rate (OR)) pattern. Glucose in blood samples were assessed for physiological changes. Data were subjected to Kruskal-Wallis tests. The result showed that concentrations of PO affected (P<0.05) the duration of NA, ER and VA behaviour in the fish species; there was no significant (P<0.05) difference between NA, ER and VA behaviour displayed by the C. gariepinus in T2 and T3. Feed responses during the experimental period were affected (P<0.05) by the different concentrations of PO, but FI and DF were similar (P>0.05) between T1 and T2. The concentration of PO increased AGO and the number of BS with the highest AGO and BS in T3. C. gariepinus in T2 and T3 displayed a similar (P>0.05) pattern of AG, MS and OR. The least frequency of AG and MS during the experiment was found in T1. The OR was affected (P<0.05) by PO exposure, and the highest OR was recorded in T3. Physiologically, exposure to PO increased (P<0.05) glucose level in blood samples of the fish species with a higher glucose value in T3. The study concluded that higher and continuous exposure to concentrations of paraffin oil could alter behavioural and physiological responses, which might impair the welfare of C. gariepinus in their habitat. It is imperative to be cautious about the quantity of PO products that get into our aquatic environments.