Endocrine Responses of Fast- and Slow-Growing Families of Channel Catfish

Sixty-eight families of USDA303 channel catfish Ictalurus punctatus were evaluated for growth performance for 30 d. The fastest- and slowest-growing catfish families were further evaluated to examine the hypothesis that genes or gene products associated with the growth regulatory and stress axes can be used to describe differences in growth performance. Research examined mRNA levels of genes involved in the growth hormone–insulin-like growth factor (GH–IGF) network in fast- (family A) and slow-growing (family H) USDA303 catfish. Fish (59.0 ± 2.4 g) were fed for 7 weeks, weighed, and had tissues for RNA extraction. The remaining fish were subjected to an acute 10-min dewatering stress. Insulin-like growth factor-II mRNA was higher in the muscle of fast-growing fish, while the levels of IGF-I receptor (IGF-IR) and IGF-II receptor (IGF-II) were similar. Muscle IGF-IIR mRNA was two-fold higher than muscle IGF-IR mRNA. There were no differences in liver and muscle IGF-I and GH receptor mRNA or pituitary GH mRNA between the fastand slow-growing fish. Fast-growing fish consumed 135% more feed than slow-growing fish, though the abundances of ghrelin mRNA in the gut and neuropeptide Y mRNA in the hypothalamus were similar. Cortisol levels were negatively correlated to weight gain. These results suggest that the variation in growth between fast- and slow-growing USDA303 catfish is explained, in part, by the variation in the GH–IGF and stress axes. The relationship between cortisol and weight gain warrants further investigation for possible exploitation in our selective breeding program

Neuropeptide y gene expression around meal time in the brazilian flounder paralichthys orbignyanus

Neuropeptide Y (NPY) is considered the major stimulant for food intake in mammals and fish. Previous results indicate that NPY is involved in the feeding behaviour of the Brazilian flounder, Paralichthys orbignyanus. In this study, we evaluated hypothalamic NPY expression before (−2 h), during (0 h) and after feeding (+2 h) in two independent experiments: (1) during a normal feeding schedule and (2) in fish fasted for 2 weeks. During normal feeding, changes in the levels of NPY mRNA were periprandial, with expression levels being significantly elevated at meal time (P<0.05) and significantly reduced 2 h later (P<0.05). Comparing the fasting and unfasted groups, NPY mRNA levels were significantly higher (P<0.05) at −2 h and +2 h in the fasting group, but there was no difference at 0 h. In addition, the higher NPY mRNA levels that were observed in the fasting group were maintained throughout the sampling period. In summary, our results show that NPY expression was associated with meal time (0 h) in food intake regulation