Ontogenetic changes of body density of larvae and juveniles in seven-band grouper Epinephelus septemfasciatus and kelp grouper Epinephelus bruneus

Abstract

Sinking death syndrome has been considered as one of the causes of early larval mortality during the seed production of seven-band grouper and kelp grouper. To elucidate the rearing period when larvae show strong minus buoyancy, ontogenetic change of body density was examined for larvae and juveniles of two species. Larvae tended to show nearly neutral buoyancy from hatching to growing to 3.5 3.9 mm in total length (TL) when the buds of the second dorsalˆn and pelvic-ˆn spines appeared. Then, body densities greatly increased with increasing the length ofˆn spines and reached a plateau at 1.060 1.070 g/cm 3 after the size of around 11 mm TL. Swim bladder in‰ation was not observed in the seven-band grouper; however, it was observed in the kelp grouper after 8.2 mm TL and the percentage of kelp grouper with in‰ated swim bladders largely increased after 18.6 mm TL.Body densities of kelp grouper with in‰ated swim bladders decreased to 1.024 1.035 g/cm 3 . It could be speculated thatˆn spines regulate the larval buoyancy by generating drag forces. It is therefore considered that larvae show strong minus buoyancy in rearing seawater at the initiation of great increase in body density whenˆn spines begin to elongate.

Promotion of initial swim bladder inflation and effect of initial inflation failure on skeletal malformation in cultured seven-band grouperHyporthodus septemfasciatus(Thunberg)

“…; Hirata et al . ), but larvae with inflated swim bladders were clearly confirmed in Experiment 1 in this study. Considering that secondary swim bladder inflation was not confirmed until at least 60 DAH (standard length 30.1 mm; TL calculated using the formula of relative growth 36.95 mm, Kitajima et al .…”

“…However, because body density greatly increased after 10–13 DAH (3.5–3.9 mm TL) when the buds of the second dorsal fin and pelvic‐fin spines appear in the seven‐band grouper, it was assumed that larvae with uninflated swim bladders tended to sink at night during that period (Hirata et al . ). As this coincides with the timing when the swim bladder initially inflates, larvae may gain buoyancy via swim bladder inflation and thus prevent sinking with the increase in body density.…”

“…In this species, removal of the oily surface film for the improvement of larval swim bladder inflation is methodologically antagonistic to the prevention of water surface mortality and, therefore, incompatible. Actually, the first priority for fingerling production is to secure seedling survival and, therefore, the non‐removal of the oil film is presently a generalized rearing method (Hirata, Hamasaki, Teruya & Mushiake ). Thus, promotional conditions for initial swim bladder inflation have not been investigated to date.…”

“…; Hirata et al . ; Tsuji et al . ), with some recording swim bladder inflation at a later stage (secondary swim bladder inflation; Kitajima et al .…”

Development of microsatellite markers for the kelp grouper Epinephelus bruneus by 454 pyrosequencing and transfer to related species

“…Bhandari et al, 2003). The other problem is that the survival of artificially reared larvae has remained low because of the high mortality rate at early developmental stages (Hirata et al, 2009). In Korea, the artificial seed production technique has been investigated since 1993, and small-scale seed production has been established since 2005 (Song et al, 2005;Lee et al, 2008).…”