The present trend of global food security in aquaculture which is focused on increasing the protein intake of every individual can only be attained through proper water management. In ensuring optimum nutrient utilization of diets and growth of tropical freshwater fishes, fish culturists must endeavour to monitor water quality parameters. The optimum production in fisheries sector is majorly dependent on the physical, chemical and biological qualities of water (Bhatnagar and Devi, 2013). It is very apparent that the health and subsequent growth of fish are directly related to the quality of water in which the fish are raised (Viadero, 2005). Fish metabolites produced as a result of biological activities and decomposition of uneaten feeds have adverse effects on the quality of water, health status and growth of the fish. Water quality parameters like dissolved oxygen, pH, turbidity, alkalinity, ammonia, temperature and other factors such as biological oxygen demand and chemical oxygen demand indicate the pollution level of given water body (Ehiagbonare and Ogundiran, 2010). It is therefore very important to note that, successful pond management requires an understanding of water quality (Bhatnagar and Devi, 2013). Water is the home of the fish and its quality has been overlooked in fish management (Keremah et al., 2014).

 

The role of water quality parameters cannot be overlooked for maintaining a healthy aquatic environment and for the production of sufficient food organisms in ponds for increasing fish production (Bhatnagar and Devi, 2013). Aquaculture productivity is determined by physic-chemical characteristics of water body (Huct, 1986). The determination of physicochemical parameters of waters in the effluents discharged from fish farms and their environmental impacts will go a long way to help fish farmers to manage and develop their waste water systems (Pulatsu et al., 2004). The production of aquatic organisms in water bodies has faced many challenges because knowledge of water quality parameters has been neglected by fish culturists.

 

The objective of this study was to investigate the effects of water exchange on water quality parameters (such as pH, water temperature, dissolved oxygen, ammonia) nutrients utilization and growth of Clarias gariepinus.

A total number of 225 C. gariepinus of mean weight 2.60 ± 0.01 g were purchased from a reputable farm in Ibadan, Oyo State, Nigeria. The fish samples were transported inside 50 L container. The fish samples were acclimatized before the commencement of the experiment for a period of two weeks in the laboratory. The fish samples were randomly assigned to five treatments and stocked at 15 fish per treatment in three replicates inside 50 L experimental bowls. The allotted fish samples were daily fed for a period of 12 weeks at 5% biomass. 

 

The fish samples were fed three times daily (7.00 am, 12.00 noon and 6.00 pm) with 2 mm Duratee pelleted feeds. Fish feeding rates were adjusted every week after measuring the total biomass of each treatment. Water was changed every day in T1 and was allotted as control while in other treatments water was changed every 2, 3, 4 and 5 days and the treatments were allotted T2, T3, 4 T4 and T5, respectively. Water samples were collected fortnightly to determine water quality parameters. The pH of the water was determined using a digital pH meter Suntex (model TS-2). Dissolved oxygen was determined using dissolved oxygen meter (model Jenway DO 9071). The dissolved oxygen meter was standardized by using saturated potassium chloride and zero solutions. The analytical determination of ammonia was determined according to the standard methods of American Public Health Association APHA (1992). 

 

After the feeding trial experiment, the following nutrient utilization and growth parameters were determined: Mean weight gain was calculated according to Ishwata (1969), by subtracting mean final weight (g) from mean initial weight (g). SGR = (LnW2 – LnW1) / T2−T1 × 100 (Brown, 1957). Where LnW2 and LnW1 are mean final weight and mean initial weight. T2 and T0 are final day of the experiment and initial day of the experiment, respectively. FCR was determined as described by Hepher (1988). FCR = Total feed consumed (g)/Weight gain by fish (g). PER was calculated according to the method of Zeiotoun et al. (1973). PER = Weight gain (g)/Protein intake

 

Statistical analysis

 

The data collected were analyzed using Statistical Package for Social Sciences (SPSS), Version 11, 2001 and Statistical Analysis Software (SAS), Version 8, 2001. Duncan’s Multiple Range Test was used to compare the differences among the means. The significant level was set at 5%.

 

The water quality parameters results are presented in tTable 1. The pH values ranged between 6.60 and 9.15. The pH value of T1 (6.60) was significantly lower compared to other treatments, while T3 (9.15) was significantly higher p < 0.05 than other treatments. The values recorded for dissolved oxygen indicated that T5 (3.47 mg/l) was significantly lower than other treatments. The ammonia values in this study revealed that T5 (0.08 mg/l) was significantly higher p < 0.05 and T1 was significantly lower than other treatments. The effects of water exchange on nutrient utilization and growth of C. gariepinus are shown in Table 2. The MWG values ranged between 21.30 g and 29.43 g. The MWG of T1 (29.43 g) and T2 (27.77 g) were significantly higher (p < 0.05) compared to other values recorded in T3 (21.30 g), T4 (21.67 g) and T5 (21.80 g). The SGR ranged between 1.99 and 2.26%. The values recorded for SGR in T1 (2.26%) and T2 (2. 22%) increased significantly p < 0.05 compared to other treatments. The FCR recorded in this experiment ranged between 0.40 and 0.52. The FCR of T3 (0.52), T4 (0.51) and T5 (0.51) increased significantly p < 0.05 than T1 (0.40) and T2 (0.42). The PER values ranged between 4.36 and 5.74. The PER of T1 (5.74) and T2 (5.31) were significantly higher p < 0.05 than other treatments.