GnRH is a neuropeptide known to regulate reproduction in vertebrates. The purpose of this study was to design and produce recombinant gonadotropin-releasing hormone associated peptide (rGnRH/GAP) as an alternative of the previous GnRHs and native extracted hormone from tissue, to induce final maturation in fish. Decapeptide as well as GAP area sequences were compared between GnRH1, GnRH2, and mGnRH from Acipenser sp and Huso huso, respectively. Considering the conserved amino acids and the replacement of unstable amino acids with those that were more stable against proteolytic digestion as well as had a longer halflife, the sequence was designed. The sequences of decapeptide and GAP region were synthesized and then cloned on pET28a expression vector and transformed into expression host Escherichia coli BL21(DE3). The supernatant of cultured recombinant bacteria was used for purification using TALON Metal affinity resin. The purity of the GnRH/GAP was confirmed by single 8 kDa band on SDS-PAGE and western blot. Bioinformatics studies were performed for evaluation of homology between GnRH protein sequences and prediction of 3D protein structure using Swiss Model. The result showed that the structure prediction of the recombinant GnRH decapeptide was relatively similar to decapeptide of GnRH2 from Beluga (Huso huso). The GAP structure was similar to GAP1 of Nile tilapia (Oreochromis niloticus) and sturgeon and GnRH2 of Chinese sturgeon (Acipenser sinensis). The mass analysis showed that the sequence was exactly the same as designated sequence. Biology activity of rGnRH/GAP was tested in mature goldfish (Carassius auratus) and results showed that rGnRH/GAP had a positive effect in final maturation. Indeed 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) was increased 17 h and 24h after injection with rGnRH/GAP and spawning stemmed from that injection. These novel findings introduce the potential of utilizing rGnRH/GAP in aquaculture.

No abstract

No abstract

No abstract

The aim of this study was to evaluate the effects of a practical diet containing different carbohydrate levels on growth rate, feed utilization, and thyroid hormones (T3 and T4) of Caspian kutum fingerlings. Fish with an initial average weight of 0.8 ± 0.2 g were fed five formulated isonitrogenous and isoenergetic diets with different carbohydrate levels of 15, 20, 25, 30 and 35 % in triplicate groups for 10 weeks. Based on the results, growth performance of Rutilus frissi was significantly affected by the dietary carbohydrate levels (P \ 0.05). Maximum weight gain, specific growth rate, and protein efficiency ratio was observed in the fish fed diet with 35 % carbohydrate. Results of thyroid hormones showed that T4 levels were not significantly different by different carbohydrate levels (P [ 0.05). The highest amount of T4 was observed in kutum juveniles fed with a carbohydrate level of 15 %. The levels of T4 were significantly affected by dietary carbohydrate levels (P \ 0.05) with the highest amount in kutum juveniles fed 15 % of carbohydrate. In conclusion, this study indicates that increasing carbohydrate levels from 15 to 35 %, with no negative effects on growth parameters in R. frissi juveniles, leads to an efficient protein ratio and optimal growth. Moreover, no clear correlation was found between fish growth and thyroid hormones.