Growth differences and growth hormone expression in male and female European eels [Anguilla anguilla (L.)]

In this study, we examined the growth differences of males and females following a sex reversion, and the growth hormone (GH) expression variation between sexes of European eels [Anguilla anguilla (L.)]. A high percentage of females (88%) was found in the group fed with estradiol 17beta compared to the control group (comprised of only 6% female eels), which was defined as the male population. Significant differences between growth rate and size were found following 480 days of growth, whereby the males reached 60+/-4.3 g (means+/-SE) in size and the females 73.4+/-5.9 (g+/-SE); after 600 days, the males reached 114.1+/-4.3 and the females 171+/-11.7 (g+/-SE). A cDNA coding for the complete growth hormone of the European eel A. anguilla (eeGH) was cloned by RACE PCR using several sets of degenerate oligonucleotides. The eeGH cDNA coding region is 627 bp long. A sequence comparison of eeGH with Anguilla japonica GH (jeGH) cDNA showed a 98% identical base. Comparison of the deduced amino acid sequence revealed 99% identical residues, meaning that a difference exists in only two of the 209 residues. In both cases, the differing residues in the eeGH amino acid sequence are lysine. We measured the mRNA levels of growth hormone in the pituitaries of male and female eels growing at different rates. A significantly higher expression of eeGH was found in the female eels in comparison to the males. These results show that different levels of GH transcription eeGH can explain the growth rate differences between male and female European eels.