Generation Cycle Closure of the Spotted Rose Snapper, Lutjanus Guttatus, in Captivity

Two natural spawns with high quality eggs (100% live embryos, 12 h after fertilization) were obtained. Spawned eggs of wild captive broodstock used to obtain F1 juveniles had 90% viability (defined as percentage floating eggs with live embryos at 12-14 h after spawning) and a hatching rate of 82-93%. Mean ± SD egg and oil droplet diameters were 750 ± 5 µm and 122 ± 2 µm, respectively. The incubation period at 35-36 and 29 - 31°C ranged from 18-20 h. Newly hatched larvae had a total length (TL) of 2.2 ± 0.2 mm. Incubation and larval rearing was carried out in 600-L cylindrical tanks (initial stocked at 20 viable eggs L^-1) from which several thousand juveniles were grown after 45-day experimental larviculture (Abdo de la Parra et al. 2010).

Nursery rearing of F1 hatchery produced juveniles was carried out in cylindrical fiberglass 5 m³ tanks, with a seawater flow of 4 volumes day^-1 and strong aeration. Lansy 1.2 mm (INVE Aquaculture, Mexico) artificial feed was supplied by hand ad libitum, four times day^-1 for 15 days. Subsequently, a formulated pelleted shrimp diet (Alimentos de Occidente, S.A. de C.V., Mazatlan, Mexico) (40% protein, 10% lipid) was supplied with two 12-h automatic feeders per tank. During the 6 months nursery stage, water temperature, salinity and dissolved oxygen varied between 22 and 29ºC, 32 to 35, and 5.0 and 6.0 mg L^-1, respectively.

From January to September 2006, a group of 400 juveniles (30-40 g BW each) were selected for the establishment of a broodstock and stocked in four 7-m³ fiberglass tanks (0.5 kg m^-3) with a sea water flow rate of 4 volumes day^-1 and strong aeration. Fish were fed to satiation once daily, 6 days per week, with a diet of fresh squid and oily fish (mostly skipjack) in equal proportions. At the end of September 2006, 78 fish were selected from the F1 juvenile group, and stocked in equal numbers into two 7-m³ fiberglass tanks, with a water flow to 6 volumes day^-1 using the same feeding practices described above. Juveniles were sampled several times during the nursery and grow-out period. In every sampling, 50 fish from each tank were anesthetized with 300 ppm of 2-phenoxiethanol (Sigma, Toluca, México) for morphological observations and determinations of TL to the nearest mm, and body BW to the nearest g.

On July 31, 2007 the TL and BW of F1 fish were determined, as well as their sexual development for their first induced spawning trial. Female gonad stage was assessed by a biopsy technique adapted to the rose spotted snapper, briefly described by Ibarra-Castro & Alvarez-Lajonchère (2011). Sexual maturity of males was based on the presence and fluidity of milt determined by light abdominal pressure, and examination of sperm motility. F1 females with a mean oocyte diameter of at least 350 µm and males with ≥ 80% motile spermatozoa were selected for the induced spawning experiments.

The laboratory tank growth of artificially produced juveniles was slow compared to the growth of commercially reared wild juveniles in floating cages (Avilés-Quevedo et al. 2008) as well as significantly slower (P < 0.05) than siblings of this progeny reared in floating cages with similar temperature and salinity conditions (Abdo de la Parraet al. 2011). The water quality and flow rate, in addition to the vital space effect of being reared in small tanks could have been the cause of slower growth in the laboratory. In Costa Rica, growth of wild spotted rose snapper has been reported faster than in Mexico, and sexual maturity is attained at a similar size, but at 2 years of age (Rojas 1997) as in the captive F1 fish at the present study, instead of the 4 years required for fish in Mexico (Amezcua et al. 2006). Also, captive fish growth is faster in Costa Rica (Boza-Abarca et al. 2008) compared to those reared in Mexico (Avilés-Quevedo et al. 2008). This suggests that there may be growth differences between the populations, as in the case of other the striped mullet, Mugil cephalus (Tamaru et al. 1993).

On July 31 2007, 5 females (BW = 687 ± 74 g; TL = 32.0 ± 1.6 cm) with a mean oocyte diameter of 360 ± 19 µm were induced with a mean GnRHa EVAc implant dose of 239 ± 20 µg kg^-1. All males had sperm with > 80% motility, and 10 were selected (BW = 553 ± 82 g; TL = 30.0 ± 1.6 cm) and implanted with a mean dose of 72 ± 26 µg kg^-1 GnRHa. During the second night, 2 females spawned (36 and 43 h after hormone-treatment), but few floating eggs were collected (90% viable eggs) (Table 1). Mean egg and lipid droplet diameters were 739 ± 17 µm and 117 ± 12 µm, respectively. These eggs had 66% hatching.

 Table 1. Induced spawning results of F1 broodstock in July 2007 and June 2008  

The next year in June 2008, 3 females (BW = 687 ± 9 g; TL = 32.0 ± 0.2 cm) and six males (BW = 745 ± 121 g; TL = 35.7 ± 2.8 cm) were selected for a second induced spawning trial. Females had a mean oocyte diameter of 410 ± 20 mm and received a GnRHa dose of 188 ± 55 mg kg^-1 while males received a mean implant dose of 70 ± 12 mg kg^-1. Two of the three females had multiple spawns (Table 1). One fish initially released a few eggs with a low percent viability 39 h after the hormone treatment and then continued for another 5 consecutive nights, spawning a mean of 172,800 ± 121 eggs with high viability of 81.6 ± 8.4%. The other female spawned during the third and fourth night after the hormone treatment and none of the eggs were fertilized. Diameter of egg and high viability percentage were 725 ± 5 µm and 80.4 ± 10% of buoyant eggs (Table 1). F2 juveniles from these spawns were reared in the same hatchery to maturity with the same methods described above, and were spawned with 2 years of age, following the same procedures (Ibarra-Castro et al. unpublished).

Authors are grateful to their colleagues at the CIAD Reproduction Laboratory, for their cooperation, and to several colleagues for their useful comments and recommendations. Our thanks are expressed to M. Ribas, for English and editorial improvements to the manuscript. This study was supported by project grants 6299-K and 6299-A from the National Aquaculture and Fishery Commission (CONAPESCA) and Mazatlan Unit of CIAD administration fund.

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