Natural spawning, early development and first successful hatchery production of the bluestreak cleaner wrasse, Labroides dimidiatus (Valenciennes, 1839), with application of an inorganic fertilization method in larviculture

Abstract

Bluestreak cleaner wrasse, Labroides dimidiatus, is one of the top ten most exported fish to the global trade in marine aquarium fish and a key species for reef fish diversity. However, knowledge on reproduction and early ontogeny of this species in captivity are scarce and incomplete. Daily spawning, early development and appropriate rearing condition (temperature and salinity) for the larviculture of L. dimidiatus were studied for the first time. We raised wrasse larvae by using an inorganic fertilization method to produce natural assemblages of phytoplankton and zooplankton, and compared it to the higher N: P ratio group and traditional rotifer-fed group. A single male dominated a harem of three females, spawning between late afternoon and dusk. L. dimidiatus spawned 305 times from 1 May 2011 to 30 April 2012, 86.9 ± 10.1% of which resulted in fertilized eggs. Fecundity ranged from 53 to 25,108 eggs per spawn with average hatching rate of 72.2 ± 22.6%. Fertilized eggs were spherical, buoyant and had a diameter of 0.68 ± 0.02 mm. Embryonic development lasted 19 h at 27.3 °C. Newly hatched larvae were 1.81 ± 0.06 mm in total length (LT) and had an oil globule in the ventroanterior area of the yolk sac. First feeding took places at 3 days post hatch (dph) which is marked by the widening of the gut. At 41 dph, transformation of larvae to the juvenile stage was completed at 12.60 ± 0.98 mm LT. On the scanning electron microscope observations, the fertilized egg membrane was smooth and lack surface sculpturing. The distribution density of pores was 61 pores 100 μm−2. The micropyle was circular or oval-shaped, and the diameter was 6.90–7.13 μm. Several neuromasts were found on the head and body surface of newly hatched larvae. The results showed that unicellular algae, zooplankton within the size ranges of 48–150 μm and larval survival of L. dimidiatus were all significantly (P < 0.05) higher in the fertilized treatment (maintaining the inorganic nitrogen and phosphorus concentrations of 700 μg N L−1 and 100 μg P L−1, respectively) compared with the others. These results indicated that the optimal conditions for embryo incubation and larval rearing of L. dimidiatus were combinations of temperature 27 °C and salinity 33 psu. Our results of this study may provide a keystone for further studies to determine the successful mass-scale production of juvenile L. dimidiatus.