Welch et al. SpringerPlus 2013, 2:634 http://www.springerplus.com/content/2/1/634 a SpringerOpen Journal RESEARCH Open Access Growth rates of larval and juvenile bigeye scad Selar crumenophthalmus in captivity Aaron Welch*, Ronald Hoenig, John Stieglitz, Zach Daugherty, Bruno Sardenberg, Sasa Miralao, Dan Farkas and Dan Benetti Abstract Growth rates of larval and juvenile bigeye scad Selar crumenophthalmus reared in captivity were studied. The results are presented, discussed, and compared to wild S. crumenophthalmus and other pelagic fish. S. crumenophthalmus are a small pelagic carangid fish of circumtropical distribution. Larvae were reared in a modified mesocosm system and sampled daily for growth. Larvae grew to a mean size of 4.74 cm (Standard Length) and 1.30 g by 45 days post hatch (dph). Larval length-at-age was best described by the exponential equation Y = 1.966e0.0704t. For juvenile growth trials, 1940 fish were stocked into four 2.5 m3 cylindro-conical tanks at two different densities (262 fish m-3 and 120 fish m-3) and reared from 45 dph to subadult stage. Fish were sampled daily for growth. No statistically significant differences in growth or survival were detected between tanks. Mean length and weight at 141 dph was 13.24 cm (Total Length) and 25.20 g. Juvenile length-at-age was best described by the Von Bertalanffy Growth -0.03(t-1.57) Model equation Lt = 27.75(1 – e ). Weight-at-age was best described by a linear equation Wt =1.7313x + 12.4662. The exponent of the length-weight equation was 3.14. In addition to providing the first published description of larviculture and juvenile growout techniques for S. crumenophthalmus, this study contains the first published data on this species’ larval growth and directly confirms estimates of S. crumenophthalmus juvenile growth done by other researchers using indirect techniques such as otolith daily growth increment and frequency distribution analysis. Keywords: Larviculture; Length-at-age; Mean daily growth increment; Von Bertalanffy Growth Model; Weight-at-age Introduction harvest (Dalzell and Penaflor 1989; Hendiarti et al. 2005). Bigeye scad Selar crumenophthalmus (Bloch) are a small Around Reunion Island in the Indian Ocean, fishers pelagic, schooling fish of circum-tropical distribution take more than 35 metric tons of S. crumenophthalmus (e.g. Dalzell and Penaflor 1989; Clarke and Privitera (known locally as atule) a year using hand lines and 1995; Mohammed and Rennie 2003; Hendiarti et al. 2005; beach seines (Roos et al. 2007). In Florida and the Roos et al. 2007). Members of the Carangidae family, Caribbeanthereisverylittlereliabledataonthemagnitude S. crumenophthalmus are an important forage fish for high of S. crumenophthalmus (known locally as goggle eye) trophic level predators, are highly valued as food in Asian harvests but anecdotal evidence indicates that landings and Pacific cultures, and are used as bait by recreational are significant, especially for use as live bait. In the and commercial fishermen all over the world (Clarke and Caribbean, live S. crumenophthalmus are the favored Privitera 1995; Honebrink 2000; Roos et al. 2007). bait of the pelagic long line fishing fleet. Individual S. crumenophthalmus support a number of important longlinevesselstakeasmanyas12,000fishtoseaper fisheries throughout the world. In Hawaii more than trip in large (~8500 l) live wells where they are used to 500 metric tons of S. crumenophthalmus (known locally target tunas (Thunnus spp.) and other high value fish as akule and hahalalu) are harvested each year for local (Capt. Don Landry, personal communication, 20 April consumption (Stevens 2004). In parts of the Indonesian 2010). In Florida, S. crumenophthalmus were formerly and the Philippine archipelagos S. crumenophthalmus harvested as a food fish, largely for sale in the Asian catches account for 3 to 15% of the annual small pelagic fish market. The fishery, however, was based on unsustain- able purse-seining practices and by the mid-1990s * Correspondence: [email protected] stocks had declined over large portions of the species’ University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA © 2013 Welch et al.; licensee Springer. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Welch et al. SpringerPlus 2013, 2:634 Page 2 of 9 http://www.springerplus.com/content/2/1/634 range. As the stocks declined, the food-fish fishery was The eggs used in this study came from two spawning largely forgotten and the S. crumenophthalmus became events that were induced using hormone injections. The increasingly valuable as live bait for recreational fishermen. first group of fish (n = 20) was injected with Luteinizing Today S. crumenophthalmus in Florida retail for $ 100 for Hormone-Releasing Hormone analogue (LHRH-a) at a dozen live fish or more (Capt. Butch Constable, personal adosageof25to50μgkg-1.Thesecondgroupoffish communication, 15 October 2008). (n = 20) was injected with Human Chorionic Gonadotropin Wild S. crumenophthalmus exhibit rapid growth rates, (HCG) at a rate of 1000 IU kg-1. Both groups were seg- reaching a fork length (Lf ) of approximately 20 to 25 cm regated in separate maturation tanks. The fish were not in one year (Dalzell and Penaflor 1989; Roos et al. 2007) sexed prior to injection. The fish injected with LHRH-a and have been observed with a Lf of more 28 cm (Ralston produced an estimated 54,400 eggs with a fertilization and Williams 1988). They are partial spawners, and have rate of 82.4% and an average diameter of 735 μm. The been estimated to release 92,000 eggs per spawn (Clarke HCG injected fish produced an estimated 62,440 eggs and Privitera 1995). In the wild, spawning occurs over an with a fertilization rate of 96.7% and an average diameter extended period during warm months (Kawamoto 1973; of 744 μm. Eggs were pooled in a single incubator and the Tobias 1987; Clarke and Privitera 1995; Roos et al. 2007). hatch rate was approximately 80%. S. crumenophthalmus arenotgenerallybelievedtosur- vive more than one spawning season, although a small Larval rearing number of animals are reported to live as long as three Approximately 71,000 yolk-sac larvae at 1 dph were years (Kawamoto 1973; Ralston and Williams 1988). stocked into a 1.8 m3 flat-bottomed larval-rearing tank Feeding is largely nocturnal and planktonic animals supplied with 1 μm filtered seawater for this study. The such as euphasiids and fish larvae are favored prey early stage larval rearing protocols used in this study items (Roux and Conand 2000). relied on a modified greenwater system adapted from other In this paper the growth rates of larval and juvenile authors (Liao et al. 2001; Papandroulakis et al. 2002; S. crumenophthalmus reared in captivity are compared Partridge et al. 2003; Palmer et al. 2007). A mixture of 50% with the growth rates of wild S. crumenophthalmus and Isochrysis galbana and 50% Nannochloropsis oculata was other wild and hatchery-reared small pelagic fish, especially maintained in the larviculture tank at a density of ~400,000 carangids. We also compare length-weight data for both cells ml-1. Due to a shortage of live algae, small amounts wild and captive juvenile S. crumenophthalmus and describe of commercially prepared non-viable I. galbana and larviculture and juvenile growout techniques for the species. N. oculata concentrates (NutrOcean, Inc., Rimouski, Quebec) were added on an as-needed basis to maintain Materials and methods the desired concentration of microalgae in the larval rearing Broodstock capture, maturation and spawning tanks. The percentage of concentrate substitution never All the fish used in this study were reared in captivity rose above 50%. Enriched s-type rotifers (Brachionus from eggs obtained from wild broodstock. All brood- rotundiformus) were maintained in the tank at a dens- stock fish used for this study were captured in wa- ity of 20–30 rotifers ml-1 via daily additions. ters approximately five nautical miles east-southeast Beginning at 17 dph the culture was transitioned from a of Key Biscayne, Florida, in the vicinity of Fowey Rocks modified greenwater system to an intensive system adapted (National Data Buoy Center Station FWYF1), latitude from Benetti et al. (2008). Water exchange was increased 25.590 N 80.097 W and held at the University of Miami (ultimately reaching 1000% per day), enriched instar-2 Experimental Hatchery (UMEH). Artemia were provided using a pulse feeding method, Broodstock fish were held in four 4.5 m3 cylindro-conical and algal and rotifer densities were allowed to drop to tanks connected to a single recirculating filtration system zero. Commercially prepared weaning feeds were pro- utilizing UV, mechanical (broken glass) and biological vided along with the live feeds beginning at 22 dph. By filtration. Each tank had its own egg collector. Brood- 35 dph the fish were fully weaned onto commercially stock fish were conditioned to spawn in their tanks by prepared feeds. maintaining water temperature at 28 - 30°C, a level that A 24-hour light photoperiod was used to rear the lar- corresponds to the upper end of the ambient temperature vae through 6 dph using aquarium lighting. At 7 dph the range experienced in south Florida coastal waters dur- photoperiod was changed to 18 hours light and 6 hours ing the S. crumenophthalmus spawning season (NODC dark. Beginning at 16 dph the light period was reduced National Ocean Data Center 2010). Natural light was by one to one and a half hours hour per day until the provided through a 95% reflective cloth. Water exchange photoperiod was entirely natural (~11 hours light and was approximately 20% per day. Ammonia (NH4)waskept 13 hours dark) at 20 dph.