Induced breeding and larval rearing of vermiculated spinefoot, Siganus vermiculatus (Valenciennes, 1835) in indoor conditions

Vermiculated spinefoot, Siganus vermiculatus has been reported to be one of the fastest growing species among genus Siganus. Even though it breeds in captivity, commercial level hatchery production is yet to be achieved. In the present study, mature brooders of S. vermiculatus (female weighing 400 g and male weighing 385 g) were induced to breed in captivity and the larvae were reared to metamorphosis. Fishes (55 nos., 150 g–700 g) were collected from the wild and reared in marine cages using formulated floating pellets as feed. Among the mature fishes brought to the hatchery, a female having an average ova diameter of 440 μm and a running male were induced with two intramuscular injections of human chorionic gonadotropin (hCG) at the rate of 500 IU/ fish and 200 IU/ fish respectively in a spawning tank. Spawning occurred on the day after the full moon, between 20- and 21 h after the second injection. Fecundity was estimated as 1.85 lakhs with 68–71% of viable eggs and hatching rate of 73–85%. Green water systems with microalgae, Nannochloropsis salina and Isochrysis galbana at a concentration of 2–3 × 10⁶ cells mL⁻¹ and 2–3 × 10⁵ cells mL⁻¹ were used in tanks (1000L) for egg incubation and larval rearing respectively. Copepod, Parvocalanus crassirostris (T1) and enriched rotifer, Brachionus rotundiformis (S-type) (T2) were tested as first feed for newly hatched larvae. The fertilised eggs (0.57 ± 0.02 mm) hatched out between 24 and 25 h and the newly hatched larvae measured 1.92 ± 0.08 mm in total length with a transparent yolk sac (0.63 ± 0.04 mm) and an oil globule (0.23 ± 0.02 mm). Mouth gape of 89.03 ± 9.4 μm was observed after 42 h post hatch. The use of copepod, P. crassirostris as the first feed helped in successful rearing of the larvae to metamorphosis and an improved survival rate (4.5%–12%). Metamorphosis was completed within 35–37 dph, during which post larvae with vermiculated body pattern measured 25.2–28.4 mm in length and 0.28–0.30 g in weight. Enriched rotifers (5–37 dph), copepodites (10–20 dph), umbrella stage of Artemia (18–24 dph), artificial pellet feeds (21–37 dph) and enriched Artemia nauplii (29–37 dph) were also used during various stages of larviculture. The present study is the first report of induced breeding of S. vermiculatus during full moon phase of lunar cycle. The results of the present study also demonstrate a protocol for successful rearing of larvae to metamorphosis with P. crassirostris nauplii as first feed.