The present study was conducted to determine whether corn gluten meal (CGM) can partially replace fishmeal and to identify its optimal CGM inclusion rate in puffer (Takifugu fasciatus) under laboratory conditions. Five isonitrogenous (45.38 to 45.64% crude protein) and isoenergetic (22.03 to 22.21 kJ/g gross energy) experimental diets were formulated. Diet 1 contained no CGM and served as control diet. Diets 2 to 5 contained 5, 10, 15, and 20% of CGM, which replaced 7.4, 14.8, 22.2, and 29.6% of fishmeal protein of the control diet, respectively. After 2 weeks of acclimation period, 11 fish (initial body weight = 41.26 ± 1.09 g; initial fish length = 12.94 ± 0.22 cm) were randomly selected and stocked into each of 15 aquaria. Experimental diets were randomly assigned to triplicate groups of fish. The results showed that there was no significant difference in weight gain, weight gain ratio (WGR), length growth ratio (LGR), food conversion (FC), and relative fatness among fish fed control diet, 5% CGM diet, and 10% CGM diet. Fish fed 15% CGM diet and 20% CGM diet had significantly lower weight gain, WGR, LGR, and relative fatness, but had significantly higher FC than fish fed the control diet. Increasing CGM percentage from 0 to 10% had no influence on apparent digestibility coefficient of protein and total essential amino acids. However, the further increase in CGM percentage from 10 to 20% significantly decreased apparent digestibility coefficient of protein and total essential amino acids. It is concluded that the upper limit of CGM for optimal growth performance and digestibility in puffer feed was 10%. Up to 14.8% of fishmeal protein of the control diet could be replaced by CGM protein without adverse effect on growth performance and digestibility of puffer.

The molecular regulation of the trypsin activity and the effects of corn gluten meal (CGM) on the trypsin activity and gene expression in Fugu obscurus were examined. The fish were fed with diets containing 0, 50, 100, 150, and 200 g kg⁻¹ CGM for 60 days. The trypsin activity and mRNA levels in the intestine, stomach, and hepatopancreas were measured before and after the experimental feeding. Enzyme activity was highest in the intestine, and mRNA expression was highest in the hepatopancreas prior to feeding the experimental diets. The effect of dietary CGM on the trypsin activity was dependent on the concentration. Enzyme activity was significantly lower in the hepatopancreas and stomach of the 200 g kg⁻¹ treatment group than in control group. In contrast, activity was enhanced in the stomach of the 100 g kg⁻¹ treatment group. Different amounts of CGM in the diets also resulted in significant changes in the trypsin mRNA levels in all three tissues. The trypsin mRNA expression in stomach, hepatopancreas, and intestine increased with increasing CGM from 0 to 10% and decreased with increasing CGM from 10 to 20%. The trypsin mRNA expression was highest in the 100 g kg⁻¹ treatment group, which was significantly higher than that of in the control. In addition, the changes in the trypsin mRNA expression levels were not reflected by changes in the trypsin activity. Our results suggest that the trypsin activity is regulated not only at the transcription level but also during translation and posttranslational modification.

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