Yousef S. Al-Hafedh

Operation of a Water Recirculating Greenwater System for the Semi-Intensive Culture of Mixed-Sex and All-Male Nile Tilapia, Oreochromis niloticus

Abstract Recirculating greenwater aquaculture technology is an appropriate method for producing commercial quantities of tilapia in locations that have water scarcity. Greenwater systems achieve three major goals; higher fish production, maximum water recycling (> 98%) and nutrient utilization. Some nutrients are recycled back in this system to sustain the development of photosynthetic algae and nitrifying bacteria creating a “suspended growth treatment process” that maintains adequate water quality. In this study, the greenwater system was implemented in triplicate, each replicate had a fiberglass fish culture tank and a cone bottomed clarifier for solid filtration. Water from the fish culture tanks is pumped to the cone clarifier through the airlift and the outflows of the cone clarifiers trickled back to the fish culture tanks at a rate of 7–8 L/minute. The study was designed to compare the performance of a greenwater system with mixed-sex, as well as, all-male tilapia. Culture tanks were stocked at a density of 40 fish/m3 with mixed-sex Nile tilapia, Oreochromis niloticusfingerlings and fed ad libitum with floating pellets containing 34% protein. The water temperature was maintained at 28±1°C, intensive aeration was provided and sludge was collected twice daily from the clarifiers. Fish were harvested after six months and culture tanks were restocked for another six months with hand-sexed all-male Nile tilapia fingerlings at a density of 40 fish/m3. Values of critical chemical parameters in the water were found to be well within the acceptable limits based on weekly water sampling. The mean final weight (±SD), final biomass, growth rate, SGR, FCR, and percent survival for the mixed-sex tilapia was found to be 287.09 (94.63) g/fish, 11.25 kg/m31.43 g/fish/day, 1.27%, 1.77%, and 97.92%, respectively. Values for the mean final weight (±SD), final biomass, growth rate, SGR, FCR, and percent survival for all-male tilapia populations were 359.67 (80.69) g/fish, 14.63 kg/m31.75 g/fish/day, 1.29%, 1.64%, and to 98.05%, respectively. Contrasting to the semi-intensive aquaculture in Saudi Arabia where 20–50% of the total water is exchanged daily to produce 8–15 kg fish/m3 of water, 12–15 kg of fish/m3 was produced with addition of only 1% of the total water daily. Only 180 liters of water was consumed to produce one kg of fish in the system.

Replacement of Fishmeal by Single Cell Protein Derived from Yeast Grown on Date (Phoenix dactylifera) Industry Waste in the Diet of Nile Tilapia (Oreochromis niloticus) Fingerlings

Isonitrogenous and isocaloric diets (32% protein, 4.3 Kcal/g) were formulated to replace fishmeal by single cell protein (SCP) from two yeasts, Saccharomyces cerevisiae and Candida utilis, grown on date (Phoenix dactylifera) processing waste in diets for two size groups (avg 15.39 g and 25.14 g) of juvenile Nile tilapia (Oreochromis niloticus). A control diet (T1) with fishmeal and six experimental diets (S1, S2, and S3 with S. cerevisiae, and C1, C2, and C3 with C. utilis) each containing 11.6%, 23.2%, and 34.2% yeast as SCP were prepared to replace 25%, 50%, and 75% of fishmeal, respectively. Tilapia fed on the control and experimental diets (S1, S2, C1, C2) with 25% and 50% replacement of fishmeal showed better growth and feed utilization. Fish fed on diets S3 and C3 (75% fishmeal replacement) had significantly (p < 0.05) poorer growth suggesting that yeast SCP can replace up to 50% of fishmeal in juvenile tilapia diets.

Effects of Dietary Protein Level on Growth, Feed Conversion, and Protein Efficiency Ratio of Freshwater Prawn, Macrobrachium rosenbergii, in Outdoor Concrete Tanks

ABSTRACT Isocaloric diets with 25,30, 35,40, and 45% protein levels were fed to triplicate groups of juvenile (1.96 ± 0.2 g) freshwater prawn, Macrobrachium rosenbergii, at 3% to 6% body weight per day for 168 days. No significant effect of dietary protein level on weight gain, specific growth rate, and survival was found (P > 0.05). Highest wet weight gain was recorded for prawns fed 35% protein diet and the poorest for prawn fed 25% and 45% protein diet. Protein efficiency ratio (PER) progressively and significantly (P < 0.05) decreased with increasing level of dietary protein. The results of the present study suggest that dietary protein requirement of freshwater prawn is 35%.

Effect of dietary fish meal replacement by red algae, Gracilaria arcuata, on growth performance and body composition of Nile tilapia Oreochromis niloticus

A 12-week long feeding experiment was initiated to evaluate the effect of dietary supplementation of red algae, Gracilaria arcuata, on the growth performance, feed utilization and body composition of Nile tilapia Oreochromis niloticus (Linnaeus, 1758). The fish were fed with an algae-free control diet (C) and three experimental diets which replaced conventional fish meal with varying levels of dried G. arcuata (20%, 40% and 60%, represented as G20, G40 and G60, respectively). The growth parameters of final weight (FW), weight gain (WG), percentage of weight gain (WG%), daily growth rate (DGR) and specific growth rate (SGR) were significantly reduced (P < 0.05) at all levels of algae incorporation compared to the control diet. Moreover, the negative impact of Gracilaria meal on the growth performance of Nile tilapia increased as the proportion of algae in the diet increased, with fish on diet G20 exhibiting a significantly higher growth performance than the fish on either of the G40 and G60 diets. On the other hand, the feed utilization parameters feed conversion ratio (FCR) and protein efficiency ratio (PER) did not show significant differences between the fish in the control group and those on diet G20, although poorer FCR and PER outcomes were achieved in the case of fish on diet G60. The content of moisture, protein and ash in muscle and carcass increased as the proportion of Gracilaria meal in the diets increased, but the reverse was true for lipid level. These results indicate that incorporation of less than 20% red algae, Gracilaria arcuata, could be feasible in the diet of Nile tilapia and further studies are recommended to optimize the level of algae to improve growth performance.