22 September 2009 First breeding of the spangled emperor, Lethrinus nebulosus (Forsskäl, 1775), in the United Arab Emirates Omer M. Yousif, Krishna Kumar and Abdul Fatah Alia1 The spangled emperor Lethrinus nebulosus, locally known as Sheeri, is a top grade food fish in the United Arab Emirates (UAE) with a high market demand the year round. The fish, the largest representative of the family Lethrinidae, has a wide geographical distribution ranging from Indo-West Pacific, Red Sea, Arabian Gulf and East Africa to southern Japan and Samoa. The fish is a marine species occurring in a variety of habitats from coral reefs to seagrass beds and mangroves, from nearshore to at least 75 m. The adults are usually solitary but are sometimes found in small aggregations; juveniles form large schools in shallow, sheltered sandy areas. Like other members of the family Lethrinidae , L. nebulosus is a carnivorous bottom feeder that exists mainly on echinoderms, bivalve and gastropod molluscs, crustaceans and, to some extent, on polychaetes and fish (Brothers et al. 1983, Carpenter and Allen 1989, Randall1995, Kulmiye et al. 2002). The fish has an elongated to oval, pale yellowish brown body with dark brown edges on the scales and a light blue spot on many scales on the upper half of the body. Three blue streaks or series of blue spots radiate forward and ventrally from the eye. The fish are protogyrous hermaphrodites, maturing first as females and then become males within a size range of 17 – 54 cm (Brothers et al. 1983, Carpenter and Allen 1989). They reach sexual maturity after 5-6 years (45 cm in length). Litherinidae is listed among a number of families of coral reef fishes that may aggregate to spawn (Domeier and Colin 1997, Claydon 2004). The fish spawns in open waters throughout the year with a peak in April. Spawning usually follows the lunar cycle, with increases in spawning frequency during the first and last quarters of the moon. Spawning events of marine finfish correlated with lunar cycles take advantage of maximum tidal flows to flush embryos and larvae offshore to a more predator-free environment and, ultimately, return them to recruitment sites along inner shelf areas (McFarland 1982). It has been shown that this species exhibits several traits desirable for aquaculture (Brothers et al. 1983, Carpenter and Allen 1989). This article reports the initial work carried out to evaluate the possibility of captive breeding of spangled emperor at Abu Al Abyad Island, United Arab Emirates. Brood Stock Collection Large numbers of ripe spangled emperor were observed to aggregate between the end of March and end of April each year along an artificially dredged channel associated with Abu Al Abyad Island. The channel was on the southeast part of the Island where a few small coral colonies occurred. It was 8 m deep with a silty bottom and good tidal water exchange. The salinity during the aggregation period was 52 ppt and the water temperature was 24-27°C. The fish aggregations were so dense that fish lay horizontally on top of each other and they were easy to approach and capture by hand. The same behavior has been reported for other Lethrinus species (Hamilton 2005). A number of running ripe fish were selected from the aggregations on April 4 as spawners. Ten females with an average weight of 1.48 kg and 10 males averaging 1.38 kg were transferred to the hatchery where the females were injected with HCG at 500 IU/kg body weight and then randomly placed for spawning into two nets (5 x 5 x 2.5m, 30mm mesh nylon) hung in two indoor oval 40 t (30 t water volume) concrete spawning tanks at a density of 10 fish/net (5 ♀:5 ♂). Quinaldine was applied for general handling of broodfish during transportation to the spawning tanks. Filtered and disinfected seawater (52 ppt) was continuously supplied at 31.25 L/min, allowing a 150 percent daily water exchange. Fish in the spawning tanks were fed squid meat ad libitum. During the spawning season the water temperatures ranged from 24-25ºC and the photoperiod was kept at 12 L:12 D. Spawning and Hatching Spawning took place 48 hrs after hormone injection in the early morning hours. The eggs were small, spherical and buoyant (pelagic). They were non-adhesive and ranged in diameter from 784-838 μm. Each had a single oil globule that was150 μm in the diameter. Spawning was continuous at both the first and second quarters of the moon, suggesting that the fish did not exhibit lunar spawning rhythm in captivity. The floating eggs were collected twice daily (0800 and 1700 hrs) using fine meshed (220 μm) collection buckets placed at the overflow of the spawning tanks. To eliminate foreign material and milt, the
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