Growth of the rabbitfish Siganus randalli Woodland - University of ...

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PRODUCTION OF JUVENILESSPAWNING AND LARVAL REARINGMost of the broodstock were descendants of 13 juveniles of Siganus randalli collectedfrom low-salinity waters (6 ppt) of the inner portion of Apra Harbor at Guam. The fish werereared to maturity in a 206-m 2 cement pond, I m in depth, at the Guam AquacultureDevelopment and Training Center. These broodstock were fed pelletized feed atapproximately 3 percent of their body weight per day. Progeny from these fish were used tobuild up the number of broodstock to approximately 300 fish; these formed the pool ofindividuals from which spawners were selected for the larval-rearing trials described below.Additional S. randalli were occasionally captured from around Guam and added to thebroodstock.SpawningTo select spawners, we collected egg samples by cannulating fish that had beenanesthetized with MS-222 (tricaine methane sulphonate). Six to eight fish, usually 75%females and 25% males, were placed in either a 2- or a lO-ton tank. If spawning did notoccur spontaneously within two days, it was induced by injecting each fish intramuscularlywith Human Chorionic Gonadotropin (HCG) at a dose of I IU g.'. The fish usually spawnedbetween midnight and dawn.Like most siganids, this species has demersal, adhesive eggs. The eggs of S. randalliare spherical with multiple oil globules (Fig. 2). We placed sheets of corrugated plastic onthe bottom of the spawning tanks to collect the eggs. Within a few hours after the larvaehatched, we removed the corrugated sheets, along with any remaining unhatched eggs and theresiduum of the hatched eggs.Larval RearingSpawning usually occurs before dawn, with the eggs hatching in the evening at theambient temperatures (usually between 28-30°C) of the outdoor tanks. The initial larvaldensities ranged from 20 to 30 \"' . We maintained the flow of seawater into the rearing tanksto provide an exchange rate of 20% of the total tank volume per day. Larval rearing was alsoconducted in the outdoor tanks.The day after hatching, phytoplankton (either Chlorella sp. or Nannochloropsisocculata) was introduced into the larval rearing tanks, at densities of approximately 5 x lOscells mI·'. During the afternoon of the second day after hatching, small-strain (S-type) rotifers(Brach ion us plicalilis--obtained from the Brackishwater Aquaculture Center at Phuket,Thailand) were added at densities of 10 to 20 m\" '. In some cases, cope pods (Tisbeh%lhuriae) appeared in the tanks during the rearing trials and provided a supplemental feed3
for the larvae. Twelve to fourteen days after the siganids hatched, newly hatched Arlemianauplii were added to the larval rearing tanks at densities of 1 to 2 mi" and later at 3 to 5mr'. After metamorphosis, commercial salmon mash was added to the diet. Similar methodsof rearing larval siganids have been used by other investigators (Bryan and Madraisau, 1977;Tawada, 1991; Duray and Kohno, 1988; Soletchnik, 1984; May et aI., 1974)Newly hatched larvae are small (1.4 to 1.8 mm in length) and lack pigmented eyesand a functional mouth (Fig. 2). Approximately 24 hours post-hatching, the eyes becomepigmented and the mouth becomes functional (Fig. 3). Soon after the mouth becomesfunctional the larvae can feed on S-type rotifers. Table I provides a generalized summary ofthe development of S. randalli larvae and the associated feeding regime.Although we were able to rear larvae of S. randalli successfully to the juvenile stage,hatchery production was limited and highly variable. A particularly critical period, one inwhich most of the larval mortalities occurred, is the transition from the yolk-sac stage to firstfeeding. Work in our laboratory is currently focusing on this transitional stage. Larvalmortality during this stage must be reduced in order to achieve the production levels requiredto support commercial aquaculture.4
Page 1 and 2: Growth of the rabbitfish Siganusran
Page 3 and 4: ACKNOWLEDGEMENTSThis work was suppo
Page 5: Figure 1. Adult of Siganus randal/i
Page 9 and 10: TABLE 1. Generalized pattern of dev
Page 11 and 12: TABLE 2. Composition of the commerc
Page 13 and 14: groups until three tanks had been a
Page 15 and 16: TABLE 5. Mean initial and final wei
Page 17 and 18: TABLE 8. Mean initial and final sta
Page 19 and 20: TABLE 12. Calculation of apparent f
Page 21 and 22: 3.253.00.........>.0"'0~ 2.75'-'CD+
Page 23 and 24: DISCUSSIONComparison of dietsBetter
Page 25 and 26: FIELD GROWTH TRIALSTo allow farmers
Page 27 and 28: Since, in our study, the juvenile r
Page 29 and 30: The major problems encountered in t
Page 31 and 32: LITERATURE CITEDAndrews, 1.W. and 1
Page 33: Woodland, D.J. 1983. Zoogeography o

Growth of the rabbitfish Siganus randalli Woodland - University of ...

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