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In this research, mass production of freshwater rotifer, Branchionus calyciflorus, for aquaculture in southeastern Nigeria, using different food types (Chlorella sp., Spirulina sp and Baker's yeast) was investigated. Rotifer stock culture was prepared using Nitrogen phosphorus Potassium, (NPK) + urea (50 : 2.5 g) and chicken droppings (25 g) with freshly grown alga. Different food concentrations (150, 300, 650 and 1000 mg/ml) and feeding intervals (2x and 3x per day) were used to grow B. calyciflorus in a Batch culture method. The highest population growth was attained with 650 mg/ml of Chlorella sp. (213.81±9.94 individuals/ml), followed by Baker's yeast (196.67±8.18 individuals/ml) and 300 mg/ml of Spirulina sp. (151.90±7.98 individuals/ml). The least population growth of B. calyciflorus was recorded with 150 mg/ml concentration of Chlorella sp. and Spirulina sp. (81.43±6.19 and 75.71±5.12 individuals/ml, respectively), and 1000 mg/ml of Baker's yeast (from local market) (65.24 ±3.86 individuals/ml). The peak population growth was attained on day 8 of experiment (p < 0.05). This study indicated that both the quantity and quality of food type have significant role on mass production of rotifer for aquaculture.

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Sodium propanoate is in the list of approved feed preservatives. However, there is dearth of information on its biological effects on the C. gariepinus. The present study investigated the effect of sodium propanoate-preserved feed on the hepatic histomorphometric changes, oxidative stress and inflammatory parameters of C. gariepinus juveniles. One hundred juveniles of mixed sexes, assigned into 5 groups of 20 fish per group, with each group consisting of 2 replicates of 10 fish, were used for the investigation. Group A juveniles were fed basal diet, while groups B-E received basal diet incorporated with sodium propanoate at the rate of 25, 50, 75 and 100 g/15 kg of feed respectively. Treatments were done two times daily for 8 weeks. Samples (sera and liver) were collected on the last day for evaluation of a few biochemical parameters (malondialdehyde values, catalase activity, C-reactive protein levels) and histomorphometric alterations in the liver. Results indicated that fish in groups D and E had higher catalase activities, lower serum levels of C-reactive proteins and an intact hepatic histomorphormetry when compared with the control group. There was no significant difference in the plasma malondialdehyde values in all the groups. It was concluded that preservation of fish feed with sodium propanoates improved antioxidant status of C. gariepinus and protected liver histology.

Chlorella lewinii LC172265 and Scenedesmus dimorphus NIES-93 were grown with BG-11 medium and then transferred to fish seedlings' farm and the effects on changes in the pH, nitrite, total ammonia nitrogen and toxic ammonia were studied. Inoculation of the ponds with C. lewinii, S. dimorphus and the combined culture of C. lewinii and S. dimorphus significantly reduced the rise in the pH of the ponds (p<0.05). With these three cultures, the pond pH increased from 6.3±0.03 to only 6.5±0.2, 6.7±0.6 and 6.4±0.1 respectively within a period of 240 hours, as against control pond's pH which increased from 6.3±0.03 to 9.0±0.1 within the same period. Furthermore, inoculation with S. dimorphus reduced the nitrite concentration in the ponds to zero on the 144th hour and the concentration remained zero throughout the experiment. This was closely followed by the combined culture of C. lewinii and S. dimorphus which reduced the nitrite concentration to zero at 240th hour while C. lewinii was the least in nitrite removal. Toxic ammonia was also zeroed by the combined culture of C. lewinii and S. dimorphus at 144th hour of experiment which was followed by C. lewinii (at 192nd hour). Aquaculture ponds co-cultured with microalgae witnessed a maximum fry death rate of 40% which was much lower than 80% death rate observed in the control ponds. These results show that C. lewinii and S. dimorphus are very efficient in sustaining the quality of aquaculture water, and thus prolonging the length of time water can be used before changing.