Background colour influences the growth performance and feed utilization of various fish species. In the current study, the effects of different aquarium backgrounds (transparent, white, black, red, green and blue) on growth performance, feed utilization, digestive enzyme activities, flesh quality, carcass composition and haematological parameters were investigated in Asian seabass (Lates calcarifer). The fish (16.17 ± 0.02 g initial body weight) were distributed into eighteen glass aquaria (6 treatments × 3 replications) with the various background colours and reared for 10 weeks. At the end of the experiment, positive growth performance and feed utilization were observed in fish reared against transparent, white, black or green backgrounds, while negative effects were noted for fish reared on the remaining treatments (p < .05). Modulation of the main digestive enzymes was observed across the six treatments, indicating different strategies for utilizing nutrients by the fish. The activity ratio of trypsin to chymotrypsin was highest in the fish reared against a black background, followed by a white background. Flesh quality, in terms of protein synthesis capacity and protein turnover rate, indicated a significant improvement in the fish reared against white, black and green backgrounds, while the contents of myosin and actin were similar across the six colour treatments. Carcass composition and haematological parameters showed no negative effects in either of the preferred treatments. These findings indicate that the most suitable background colours for rearing Asian seabass are black, followed by white and green, while transparent, red or blue backgrounds are unsuitable.
Live diets are preferably used for rearing Siamese fighting fish (Betta splendens Regan, 1910) since they provide superior growth over the dry feed. In the current study, three different preparations of mosquito larvae were prepared (frozen at −20°C, F-20; freeze-dried and kept at 4°C, FD4; freeze-dried and kept at ambient temperature, FDAT) and were individually fed to 1-month-old red male fighting fish (1.18 ± 0.01 g initial body weight) over 6 weeks duration. At the end of experiment, there were no significant differences in growth performance and feed utilization across three dietary treatments (p ˃ 0.05). Specific activity of lipase was significantly lower in fish fed FD4 and FDAT than with the F-20 diet, while no differences in other enzymes were observed. The fish fed with FDAT diet significantly increased in viscerosomatic index relative to F-20 and FD4 treatments. Significant improvements in skin redness and flesh quality (RNA and RNA/protein ratio) were observed in the fish fed with FDAT diet relative to the other treatments. This preferred FDAT treatment also maintained the carcass composition. Analysis of digestive enzymes in FDAT mosquito larvae demonstrated the presence of protein-, carbohydrate-, and lipid-digesting enzymes after 1 month of storage. The findings from our experiments indicate that the freeze-dried form (FDAT) of mosquito larvae is suitable for rearing Siamese fighting fish. However, effective preparation protocol and appropriate storage times should be further studied. K E Y W O R D S colour, digestive enzyme, flesh quality, freeze, freeze-dry, live diet
Water volume is a key parameter affecting the individual rearing of male Siamese fighting fish (Betta splendens Regan, 1910). In this study, minimization of water volume was pursued by assessing growth, feed utilization, digestive enzyme activities, color coordinates, muscle quality, and carcass composition. One-month-old solid-red male fish (0.97 ± 0.01 g initial body weight) were distributed individually into glass aquaria with five alternative water volumes (100, 150, 200, 250, and 300 mL), comprising 15 fish per treatment (n = 15), over 8 weeks duration. No mortality of the reared fish was found during the study. Growth performance and feed utilization of the fish reared in 150 mL water were superior to the other treatments. The water volume significantly affected specific activities of the digestive enzymes (P ˂ 0.05), except for amylase, and no differences in enzyme activities were observed between fish reared in 150 and in 300 mL water. The preferred treatment maintained skin lightness (L*) and had the highest redness (a* and a*/b*) among the treatments. Protein synthesis (RNA concentration) and its turnover rate (RNA/protein ratio) and myosin and actin in muscle also benefited from this treatment. Carcass composition, in terms of moisture, crude protein, and crude ash, was maintained, but the amount of crude lipid fluctuated with water volume. Based on our experiments, the preferred minimal water volume for individual rearing of male Siamese fighting fish should be about 150 mL.
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