Histological observations of seasonal reproductive and lunar-related spawning cycles in the female honeycomb grouper Epinephelus merra in Okinawan waters

Abstract

Seasonal reproductive and lunar‐related spawning cycles of the female honeycomb grouper Epinephelus merra inhabiting Okinawan waters were examined by histological observation of ovaries. Gonadosomatic index (GSI) increased beginning in May and peaked in June. Histological observations revealed that many oocytes laden with yolk were present in the ovaries from May to August. From September to October, ovaries were occupied by immature oocytes. These results suggest that the reproductive season of E. merra lasts for 4 months from May through August in Okinawan waters. When the fish were collected according to the lunar cycle, GSI increased with the approach of the full moon. Oocytes at various development stages were observed from the first quarter to the full moon. Fresh ovulatory follicles were present in the ovaries around the last quarter moon. These results suggest that E. merra has a lunar spawning cycle and spawns between the full moon and the last quarter moon. Ovarian features of the fish collected around the last quarter moon were different among individuals; some fish had many oocytes at the tertiary yolk stage in the ovaries, while the ovaries of the others were occupied by the oocytes at the peri‐nucleolus and the oil droplet stages. This observation suggests that a minor release of eggs occurs in this species before or after a major spawning lunar day. Oocytes at the migratory nucleus and the maturation stages were not observed in any ovarian samples. This may mean that maturation of oocytes is related to the spawning behavior of this species and makes rapid progress in the process of aggregation at the spawning sites.

Immunohistochemical evidence identifying the site of androgen production in the ovary of the protogynous grouper Epinephelus merra

“…Mature ovaries contained vitellogenic or hydrated oocytes from May through July, the recognized spawning season of E. merra in Okinawa waters (Lee et al 2002;Bhandari et al 2003). During the non-spawning season, ovaries were characterized by the presence of oocytes at three stages: primary chromatin nucleolar, perinucleolar, and yolk vesicle.…”

Induction of Female-to–male Sex Change in the Honeycomb Grouper (Epinephelus merra) by 11-ketotestosterone Treatments

“…Since honeycomb groupers are lunar spawners (Lee et al , 2002;Soyano et al ., unpublished data) and prefer a very calm and quiet environment for mating, the sex-changed individuals were allowed to mate at midnight around the time of a full moon. Two 11KT-treated fish were kept with two untreated females in a separate 500-liter polyethylene tank to ensure functional sex change.…”

Reproductive cycle of leopard grouper Mycteroperca rosacea (Streets, 1877) held in captivity: relation ship between gonad development and sex steroid concentration

“…E2 changes were related to increasing daylight and temperature. The relationship between the increase in E2 levels, when daylight and temperature increase, and the advanced stages of gonad development have been shown in studies on other grouper species, such as E. morio (Johnson et al, 1998), E. merra (Lee et al, 2002;Bhandari et al, 2004bBhandari et al, , 2005Bhandari et al, , 2006, dusky grouper, Epinephelus Figure 2d. Monthly values of sex steroids are depicted as mean ± SE (n = 7).…”

“…This work differs from other sex steroids studies in which fish were sacrificed to obtain average values of a group. As done for red grouper, Epinephelus morio (Valenciennes, 1828) (Johnson et al, 1998); honeycomb grouper Epinephelus merra (Lee et al, 2002;Bhandari et al, 2004aBhandari et al, , 2004bBhandari et al, , 2005Alam et al, 2005); orange-spotted grouper Epinephelus coioides (Yeh et al, 2003); and blackeye goby Rhinogobiops nicholsii (Kroon & Liley, 2000), among others.…”