Ecological Studies of the Anthiine Fish Sacura margaritacea in Suruga Bay, Japan

Abstract

Present paper deals with ecology, behavior, and life history of Sacura margaritacea (Hilgendorf) in Suruga Bay.The species, which is sexually dimorphic and protogynous hermaphroditic fish belonging to the subfamily Anthiinae, ranges from Sagami Bay to Nagasaki along the Pacific coast of Japan.Its size is usually less than 13.0 cm in standard length.The investigations were performed using SCUBA, and were conducted mainly at two stations mostly shallower than 48 m deep (Figs.1 and 2).The stations were visited for two to five days in every month during two years, 1971-1973.After the each underwater observation, live specimens were captured for the observation in the laboratory.
S.margaritacea is found mostly in large schools in the subtidal rocky habitats more than 15 m deep (Fig.2), though few individuals were in the depth as shallow as 7 m.The schools of the fish extend to shallower area in summer, and return to deeper area late in autumn to spring.The males swim closer to sea-bottom where as the females swim around to the middle layer apart from the bottom (Fig.7).
Among 364 specimens captured, 296 were females, 79 were males, and 19 wereintermediate in sex reversal.In fork length females were in the range 64.4-124.0 mm, males were 117.5-146.0 mm, and intermediates were 111.1-127.0 mm and extremly rare (Table 2 and Fig.3).No monthly change in sex ratio through the year were observed excepting appearances of the intermediate forms (Fig.5).
Spawning season of the fish starts in August, reaches climax in September, and falls in November (Fig.6).Previous to the breeding season, a few individuals of both male and female make small groups together near the shallower bottom (about 15 m deep) at the stations.Then, the males perform the display dance toward selected females.In August, when the breeding season draws, the display by males become more active, and is frequently observed everywhere in schools.However territorial behavior are indistinct in this species.
The sex reversal in S.margaritacea takes place in the range 111.1 mm-127.0 mm in fork length and occurs mainly during the non-breeding season.
Youngs of S.margaritacea smaller than 64-65 mm in fork length are not included in schools.Youngs measuring 19.5-54.8 mm in fork length (Fig.8) were found behind the rock on sea-bottom 15-48 m deep near circumferrences of schools.Youngs were presumably younger than a year old.These Youngs appear to join schools in early summer in the next year, and to reach biological minimum size as female in one or two years after hatching.
S.margaritacea is a plankton feeder, and mostly feeds on calanoid copepods throughthe year in Suruga Bay.
Artifically fertilized eggs of the fish are bouyant, colorless, spherical, and measuring 0.78-0.80 mm in diameter.The hatching takes place 15.5 hrs after insemination, at the water-temperature of 24.3-28.5°C.The newly hatched larva, measuring about 1.46-1.52 mm in total length, has an oil-globule situated in the anterior top of yolk.The larva has 13+13=26 myotomes and the fish has 26 vertebrae.Larvae of 48 hrs after hatching are 2.40-2.46mm in total length.In this stage the posterior part of eye is black, and the mouth is open (Fig.12).
The newly hatched larvae of S.margaritacea have some remarkable features and differ from the previously known larvae of other Japanese serranids, such as Lateolablax japonicus and Epinephelus akaara.The larvae of S.margritacea have a large and oval yolk protruding anteriorly beyond the anterior point of head.Also the larvae float with the head upward.Whereas larvae of the two serranids mentioned above do not have such a large yolk, and float the head downward (Mito, 1957;Ukawa et al.1966).