| Honeycomb grouper | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Perciformes |
| Family: | Serranidae |
| Genus: | Epinephelus |
| Species: | E. merra |
| Binomial name | |
| Epinephelus merra |
|
The Honeycomb grouper (Epinephelus merra) is one of the smaller fish species in the Epinephelus genus, with a maximum known length of 31 cm. E. merra typically feeds on crustaceans and fish. E. merra is commonly found in reef environments of the Pacific Ocean, from South Africa to the areas around Australia, Japan and the surrounding islands.[1]
The honeycomb grouper is a valuable food fish. Attempts are underway to culture this species in farms. However males are rare, which limits commercial production of this fish.[2]
The genus Epinephelus has the ability to change sexes, more specifically they are protogynous hermaphrodites what means females can turn into males at one point in their life.[3] The Honeycomb grouper is studied because of its relatively small size. This sex change usually happens in the non breeding season and can be caused by social stimuli, age, growth, and body size. Yet, the initial trigger for the sex change remains unknown.[4] [4] Females turn into males when they reach a length of approximately 20 cm, thus the size advantage model for sequential hermaphroditism applies in the case of the honeycomb grouper. The size advantage model states that if an individual can reproduce more effectively as one sex when small or young and as the other sex when larger or older, it should change sex at some point in its life history.[5]
In summary, the Honeygrouper has been found to transition from female to male when low levels of estradiol-17β (E2) exists, leading to increased levels of 11-ketotestosterone (11KT). These hormonal changes lead to a degeneration of existing oocytes and trigger the sex change. When E2 levels fall below a specific physiological threshold, oocytes no longer survive and spontaneous androgen levels now initiate the proliferation of sperm producing cells. High levels of 11KT and testosterone maintain spermatogenesis.[2] [3]
Estrogen's (E2) role: Females only change sex after meeting or exceeding a length of 20 cm and during the nonbreeding season, where E2 has been found to be low. Yet it is still unknown if the drop in E2 is the cause or an effect of the sex change. In fish, it is conclusive that estrogen has a direct effect on ovarian differentiation and is needed to maintain overall ovarian development.[4] Biosynthesis of estrogen is mediated by aromatase P450. [2]
Artificial Aromatase Inhibitors (AI): When an (AI) is administered, the levels of Estrogen decrease and even immature females turn into males. However, if AI is given together with artificial E2 the fish remains female. This finding concludes that E2 plays a big role in maintaining a female gender in the Honeycomb grouper fish. Lack of Estrogen causes degradation of oocytes, and the start of sperm production. AI could be a tool to increase the breeding rates of grouper fish, by increasing both sperm count and fertility rates in the fish. .[2]
11-ketotestosterone's (11KT) role: 11-KT's levels increase in the fish in correlation with the transition from female to male. When 11KT was induced it triggered a sex change. 11KT stimulates the growth of male germ cells and their differentiation.[5]
Ovarian:Immature female, resting female, developing female, maturing female, mature female, partially running female, and post-spawning female.
Transitional: Early transitional, bisexual and late transitional.
Testicular: Maturing, mature and running ripe testes
Stages are determined by proportion between male and female tissue, female germ cell degradation, presence of male cysts arranged in lobules, and development of sperm sinuses along gonadal wall.[3]