The manipulation of the growth characteristics of aquatic organisms constitutes a high priority for the biotechnological industry, given the expected worldwide increase in food demand and the current food shortages, especially in animal protein, for significant segments of the population. The stimulation of growth, aimed at reducing the extension of harvest cycles for aquaculture and at decreasing the high mortality typical of larval stages in fish; as well as the use of immunostimulants to allow aquacultural populations to cope with the conditions of intensive culture, are two of the main targets of modern aquacultural biotechnology. Recent data about the immuneendocrine connection in fish have shown that growth hormone has a stimulatory effect on several parameters of the innate immune system. Therefore, the use of biotechnological means for the stimulation of growth hormone and, consequently, the innate immune system, is a promising mean for fulfilling this goal. The present work summarizes our study of the influence of the pituitary adenylate cyclase-activating peptide (PACAP) and the PACAPrelated peptide (PRP) from Clarias gariepinus, as well as neuropeptide Y from Oreochromis sp. on the growth characteristics and innate immune system of fish. The results show that these neuropeptides not only have growthpromoting and development-related effects, but also stimulate several elements of the innate immune response such as lysozyme, lectins, nitric oxide and anti-oxidative defenses (catalase, superoxide dismutase and reduced glutathione levels).

Growth is a complex process in fish. This study was designed to test the effect of different levels of recombinant tilapia growth hormone (tiGH) injected intraperitoneally in juvenile hybrid tilapia Oreochromis hornorum. Tilapia GH cDNA was cloned from hybrid O. hornorum tilapia. The mature protein was expressed in E. coli under regulation of the phage T7 promoter. The E. coli-derived tiGH was partially purified to 67% purity and, following renaturation, was shown to be biologically active in in vivo and in vitro assays. Recombinant tiGH stimulated extracellular matrix synthesis as shown by 35S-sulfate uptake in ceratobranchial cartilage explants. Zero, 0.1, 0.5 and 2.5 µg tiGH/g body weight (gbw) were injected in tilapia, and the effects on the growth-promoting action, hepatosomatic index (HSI), and mRNA insulin-like growth factor (IGF) induction were measured. A significant increase in the body weight (P < 0.05) and length (P < 0.01) was observed in tilapia receiving 0.5 µg tiGH/gbw. However, tilapia receiving 0.1 and 2.5 µg tiGH/gbw did not show an increase in body weight and length with respect to the control group receiving BSA injections. Binding sites for the recombinant tiGH were identified in the liver. Consistent with its somatotropic actions, the IGF mRNA induction was observed in the groups injected with 0.1 and 0.5 µg tiGH/gbw (P < 0.05). No significant increase in the HSI was detected in the injected groups when compared to the control group. These results demonstrated that the injection of biologically active E. coli-derived tiGH produces physiological changes in juvenile tilapia that ultimately resulted in a growth-promoting action only at a dose of 0.5 µg tiGH/gbw.

The generation of transgenic fish with the transfer of growth hormone (GH) genes has opened new possibilities for the manipulation of growth in economically important fish species. The tilapia growth hormone (tiGH) cDNA was linked to the human cytomegalovirus (CMV) enhancer-promoter and used to generate transgenic tilapia by microinjection into one-cell embryos. Five transgenic tilapia were obtained from 40 injected embryos. A transgenic animal containing one copy of the transgene per cell was selected to establish a transgenic line. The transgene was stably transmitted to F1 and F2 generations in a Mendelian fashion. Ectopic, low-level expression of tiGH was detected in gonad and muscle cells of F1 transgenic tilapia by immunohystochemical analysis of tissue sections. Nine-month-old transgenic F1 progeny were 82% larger than nontransgenic fish at p = .001. These results showed that low-level ectopic expression of tiGH resulted in a growth acceleration in transgenic tilapia. Tilapia GH gene transfer is an alternative for growth acceleration in tilapia.