Effectiveness administration of recombinant growth hormone through the feed with different coating materials and pelleting in Nile tilapia

Abstract

Application of recombinant growth hormone (rGH) to improve the growth of fish can be performed by injection, immersion and oral delivery method through feed. However, injection and immersion methods are relatively difficult to be applied to mass scale. Injection delivery method is time consuming and labor intensive. Furthermore, immersion method is only effective on the larval stage or small fish size, at a certain immersion dose and frequency. In addition, applications mass-scale immersion method with frequency of more than 1 time, high-potential causing fish stress. Oral delivery method is practical and time efficient. However, by this method rGH need to be coated to avoid degradation by digestive enzymes, and damage due to the low pH in the stomach. Hydroxypropyl methylcellulose phthalate (HP55) is a material often used for coating the rGH, but it is relatively expensive and inefficient when applied in large amounts. Another cellulose such as polymethyl carbamide (PMC) can also be used as a coating agent. PMC is a relatively cheap price, and has been reported to protect the coated material in a relatively long time; storage at a temperature of 20oC for about 1 year, 25 to 30oC about 6 months, and 35 to 38 °C about 3 months. Chicken egg yolk has also been widely used as a binder of medicines and feed supplements in fish. Its price is relatively cheap and easy to obtain. This study was performed to examine the effectiveness supplementation of recombinant giant grouper GH (rElGH) in tilapia feed using a variety of coating materials and pelleting on production, feed conversion, blood glucose, glycogen levels and proximate content of fish. Production of rElGH was performed using Escherichia coli BL21 containing pCold-ElGH protein expression vector. Bacteria were cultured in 2xYT media at incubation temperature of 15°C for 24 hours and protein synthesis was induced with isopropyl-bD-thiogalac-topyranoside in a dose of 0.5 mM. Lysis of bacterial cell walls was conducted using lysozyme, then total protein in inclusion body of rElGH were collected by centrifugation. SDS-PAGE analysis was used to ensure the presence of rElGH in the total bacterial protein. This study consisted of 5 treatments including the control, and each treatment was given 3 replications. The size fish used fish was 5 to 6 cm in body length. Fish were maintained at hapa installed in a concrete pond (measuring 3x2x1 m) with a stocking density of 125 fish in each hapa. Fish maintenance was carried out for 2 months. During the first 2 weeks fish were fed diet without rElGH (feed adaptation) with a frequency of 3 times a day, and then fed on rGH-supplemented diet in 3 times at intervals of 3 days. The results showed that chicken egg yolk coated rGH treatment generated significantly biomass (P<0.05) compared to the control (1262.2 ± 96.4 g). Fish biomass among treatments was similar (P>0.05). Increase in biomass in chicken egg yolk coating was 46.85%, 32.50% by HP55, 27.99% by PMC, and 26.64% by pelleting method compared with the control. In addition, specific growth rate (SGR) of fish treated by HP55, chicken egg yolk, and PMC coated rGH were significantly higher (P<0.05) compated to control. SGR of chicken egg yolk coating treatment was about 34.3% higher compared to the control. In addition, fish feed conversion rate among treatments and control were similar. Meanwhile, survival of rElGH treatments were higher than control (P<0.05). Survival of rElGH treated fish was 96.80 to 97.33%, while the control was 93.07%. Protein retention in fish treated by rElGH with different coating materials was similat to that of control (P>0.05), while lipid retention in PMC coating treatment was significantly lower (P0<0.05) than that of other treatments and control. Lower blood glucose level was obatined in pelleting treatment, while other treatments and control was (P>0.05). Liver glycogen content in chicken egg yolk coating treatment was higher than other treatments and control, while muscle glycogen content was similar among coanting treatments and control (P>0.05). In conclusion, administration of rElGH through feed could significantly improve the growth of Nile tilapia. PMC and chicken egg yolk can be used as a substitute for HP55. Coating of rElGH did not affect protein retention, while lipid retention was affected by coating materials used.