ADVANCES IN YELLOW TANG Zebrasoma flavescens CULTURE
Yellow Tang (Zebrasoma flavescens) is a significantly important reef species in Hawaii representing over 80% of the catch for the aquarium trade by value. Although this species has been under investigation in our labs since early 2000, progress with their culture has been very limited. Early efforts to rear this species will be reviewed and compared to the recent results of the most successful hatchery run to date.
Yellow Tang broodstock were held in 20 m3 tanks receiving 6-8 turnovers daily of saltwater (26-27˚C at 31-33 ppt). The fish spawned naturally each month, with a peak egg production occurring around the full moon. Eggs were stocked into 1,000 L fiberglass tanks (40 eggs L-1). Gentle aeration was provided by two submerged airstones near the tank center, which caused an upwelling current. The larval rearing tanks received 8-10 daily turnovers of 1 µm filtered, UV irradiated seawater. The photoperiod was 24L:0D (1500 lux measured at the tank surface). The eggs hatched after about 20 h (26˚C) into very primitive larvae that began feeding at 3 days post hatch (dph). Larvae were fed Parvocalanus crassirostris nauplii at a density of 1-5 individuals mL-1 two times daily. Later stage (N3-N5) nauplii, copepodites, and Artemia nauplii were offered to the larvae from 30 dph onward. No background algae were used in the larval rearing tank.
The earliest feeding larvae were observed to primarily ingest copepod eggs and N1 stage nauplii. Significant mortality was observed just past first-feeding (5-7 dph). However, several thousand larvae (approximately 20% of the starting number) survived this critical period and persisted from 10-30 dph with little observable attrition. Larvae formed large, extended dorsal and ventral spines by 14 dph which persisted through flexion at 26 dph and began to recede after 60 dph.
Yellow Tang were reared to 83 dph marking a significant milestone for this species and for the family Acanthuridae (of which no member has been cultured). Although the larvae achieved flexion by 26 dph, development slowed rapidly from 30-60 dph. This was likely due to the fact that the live prey being offered (copepods and Artemia) were not suitable for the later stage larvae. The lack of suitable prey and/or the correct environmental cues may have resulted in delayed settlement. During this period, we observed daily mortality of the largest individuals, presumably due to these factors. Although settlement of Yellow Tang larvae was not observed, we now have a much better understanding of the challenges that lie ahead with culturing the later larval stages of this species.