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Creatine plays a vital part in the energy metabolism and physiological roles. It is exclusively found in ingredients of animal origin, so using all‐plant protein‐based diets increases the risk of creatine deficiency. The objectives of this current study were to determine the optimal level of dietary guanidinoacetic acid (GAA) with regard to the nutrient digestibility, growth performance, feed utilization and carcass quality of Nile tilapia (Oreochromis niloticus). The fish (27.33 ± 0.70 g) were fed with five different isonitrogenous and isoenergetic diets for 60 days: T1 was the positive control diet (HF; 6% fish meal inclusion); T2 was the negative control formulated to contain no GAA (NC, free fish meal); and T3, T4 and T5 were NC supplemented with 0.06%, 0.12% and 0.18% of GAA respectively. At the end of the experiment, it was found that growth performance and feed utilization were not significantly different (p > .05) among the groups. However, fish from the T3 and T4 groups had slightly better weight gain and growth rate, as well as improved digestibility of protein, methionine, lysine and histidine (p < .05). Fish fed the dietary GAA at 0.06 or 0.12% had clearly larger width increment than the other groups. This is important as consumers prefer large dorsal muscles. This result from this study showed no adverse effect on haematological parameters, serum biochemistry parameters, fillet texture quality and histopathological change in the liver of Nile tilapia. Therefore, these results indicate that GAA supplementation at 0.06%–0.12% in Nile tilapia diet can potentially improve fish growth and feed utilization without setback on health.

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This research was aimed to study on biological aspects of giant snakehead fish (Channa micropeltes) in Huai Suea Ten wetland site, Nam Phong District, Khon Kaen Province in Thailand between April, 2017 and March, 2018. Thirty-six fish species belonging to 17 families were observed at 10 sampling sites. Three Channidae fishes, namely snakehead fish (Channa striata), giant snakehead fish (Channa micropeltes), and forest snakehead fish (Channa lucius), belonging to the family Channidae were reported. A total of 230 giant snakehead fish were found in this survey which consisted of 118 males and 112 females. The sex ratio (male: female) was 1:0.95. The gonadosomatic index value of the female (0.79±0.05%) was higher than that of the male (0.25±0.08%). The body length and body weight of a total of 230 giant snakehead fish observed in this study showed the average of a total body length was 43.71±11.72 cm; and the average of the body weight was 448±173 g/fish. The condition factor of giant snakehead fish observed in 12 months were in a range of 0.45-0.74 for the male and 0.39-0.70 for the female. The ratio of the body and intestinal length of giant snakehead fish was as 1: 0.70. The stomach digesta components, expressed as the percentages of a whole stomach content weight of this fish species consisted of 51.8% of fish fillet, 30.3% of small fish and 17.9% of digested digesta.

Nile tilapia (Oreochromis niloticus) is one of the most important cultured fish species worldwide (Gu et al., 2017). Its cultivation at high densities in floating cages is practiced in large lakes and reservoirs of several countries, namely, China, Indonesia, Mexico, Honduras, Colombia, Brazil and Thailand. However, animals cultured under an intensive system are often subjected to stress conditions that can