Cloning and characterization of two types of growth hormone receptors in tomato clownfish (Amphiprion frenatus), and their expression under different light spectra and photoperiods

Light is regarded as an important environmental factor which is involved in the regulation of the various physiological processes of fish. Thereinto, the light spectra and photoperiods have been shown the noticeable influences on the growth performance of fish species. In the present study, two types of growth hormone receptors (Afghr1 and Afghr2) were cloned from tomato clownfish (Amphiprion frenatus) using RACE PCR, and the effects of different photoperiods and light spectra on the growth performance as well as the growth-related gene expression of A. frenatus were investigated. The full-length cDNA sequences of Afghr1 and Afghr2 were 2609 and 2673 bp in length, encoding the proteins of 630 and 571 amino acids, respectively. Both receptors were widely expressed in all the tested tissues, and the highest expression was observed in the liver and pituitary, respectively. Furthermore, the experimental clownfish under constant-light photoperiod (24L:0D) exhibited the significantly higher related somatic growth rate and expression levels of Afghr1, Afghr2, gh, and igf-I as well as the lower feed conversion ratio and plasma melatonin level, compared with other photoperiods (16L:8D, 8L:16D, and 2L:22D). Additionally, red light appeared to markedly improve the growth parameters and the expression of growth-related genes comparing with blue, green, and white lights. In summary, the result of the current study highlights the regulatory effects of light spectra and photoperiods on the growth performance of a coral-reef fish, A. frenatus. The constant-light photoperiod (24L:0D) and red light have been shown the best promotion for the growth of A. frenatus and should be considered as the optimal light conditions for its culture.