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ABSTRACT: Traditionally, sciaenid eggs have been identified based on morphological characteristics such as size, number of oil globules
and/or pigmentation patterns. Identification of sciaenid eggs by these procedures is time consuming and often inaccurate due
to considerable egg size overlap among species. The utilization of molecular techniques for the identification of economically
important species has become a fundamental component in ecological studies involving fish eggs and larvae. This study reports
the development of a series of both multiplex and individual polymerase chain reactions to identify the eggs of 11 sciaenid
species commonly found in the Gulf of Mexico and estuaries near Port Aransas and Corpus Christi, TX, USA. Following method
development, the discriminatory power of the assay was first determined with samples from adult fish collected from Aransas
and Corpus Christi Bays, Galveston Bay and the lower Laguna Madre in northern Mexico. Most (97%) of these fishes were correctly
identified to the level of species. To demonstrate the applicability of the assay, wild fish eggs were collected and analyzed
from the Aransas Pass tidal inlet from September through December 2005. During this period, the eggs of four target species
were positively identified which was in keeping with current knowledge regarding the spawning areas and seasons of these sciaenids
based on the presence of mature females, eggs and/or larvae. Future use of this method can provide valuable information to
better discriminate spawning sites and seasons of these species.
Marine Biology 04/2012; 157(8):1889-1895. · 2.28 Impact Factor
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ABSTRACT: Interactions between the thyroid hormone (TH) and corticosteroid (CS) hormone axes are suggested to regulate developmental processes in vertebrates with a larval phase. To investigate this hypothesis, we isolated three nuclear receptors from a larval acanthomorph teleost, the red drum (Sciaenops ocellatus), and established their orthologies as thraa, thrb-L and gra-L using phylogenomic and functional analyses. Functional characterization of the TH receptors in COS-1 cells revealed that Thraa and Thrb-L exhibit dose-dependent transactivation of a luciferase reporter in response to T3, while SoThraa is constitutively active at a low level in the absence of ligand. To test whether interactions between the TH and CS systems occur during development, we initially quantified the in vivo receptor transcript expression levels, and then examined their response to treatment with triiodothyronine (T3) or cortisol. We find that sothraa and sothrb-L are autoregulated in response to exogenous T3 only during early larval development. T3 did not affect sogra-L expression levels, nor did cortisol alter levels of sothraa or sothrb-L at any stage. While differential expression of the receptors in response to non-canonical ligand hormone was not observed under the conditions in this study, the correlation between sothraa and sogra-L transcript abundance during development suggests a coordinated function of the TH and CS systems. By comparing the findings in the present study to earlier investigations, we suggest that the up-regulation of thraa may be a specific feature of metamorphosis in acanthomorph teleosts.
General and Comparative Endocrinology 03/2012; 176(1):39-51. · 3.27 Impact Factor
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Journal of Experimental Marine Biology and Ecology 01/2012; 432-433:186-190. · 1.88 Impact Factor
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ABSTRACT: The present study describes the distribution of an arginine vasotocin (AVT) V1a receptor (AVTr) throughout the brain of a sex-changing grouper, rock hind Epinephelus adscensionis. The objectives of this study were to describe the AVTr distribution in the brain of rock hind for potential linkages of the AVT hormone system with sex-specific behaviors observed in this species and to examine sex-specific differences that might exist. An antibody was designed for rock hind AVTr against the deduced amino acid sequence for the third intracellular loop. Protein expression, identified with immunohistochemistry showed high concordance with mRNA expression, identified with in situ hybridization. AVTr protein and mRNA expression was widely distributed throughout the brain, indicating that AVT may act as a neuromodulator via this V1a receptor subtype. AVTr protein and mRNA were present in regions associated with behavior, reproduction and spatial learning, as well as sensory functions such as vision, olfaction and lateral line sensory processing. We observed high AVTr expression in granular cell formations in the internal cellular layer of olfactory bulbs, torus longitudinalis, granular layer of the corpus cerebellum, valvula of the cerebellum, nuclei of the lateral and posterior recesses, and granular eminence. High protein and mRNA expression was also observed in the preoptic area, anterior hypothalamus, and habenular nucleus. No obvious sex differences were noted in any region of the rock hind brain.
Journal of chemical neuroanatomy 06/2011; 42(1):72-88. · 1.75 Impact Factor
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ABSTRACT: Hermaphroditism, associated with territoriality and dominance behavior, is common in the marine environment. While male sex-specific coloration patterns have been documented in groupers, particularly during the spawning season, few data regarding social structure and the context for these color displays are available. In the present study, we define the social structure and male typical behavior of rock hind (Epinephelus adscensionis) in the wild. In addition, we detail the captive conditions and time period necessary to induce the onset of the sex-specific coloration and sexual change. At six oil production platform locations in the Gulf of Mexico, rock hind social group size and typical male rock hind social behavior were documented. We observed a rapid temporary color display in rock hind that could be turned on and off within three seconds and was used for confronting territory intruders and displays of aggression towards females. The male-specific "tuxedo" pattern consists of a bright yellow tail, a body with alternating dark brown and white patches and a dark bar extending from the upper mandible to the operculum. Identification and size ranges of male, female and intersex fish collected from oil platforms were determined in conjunction with gonadal histology. Rock hind social order is haremic with one dominant male defending a territory and a linear dominance hierarchy among individuals. In five captive experiments, the largest remaining female rock hind displayed the male specific color pattern within 32d after dominant male removal from the social group. To our knowledge, this is the first evidence in a grouper species of color patterning used to display territoriality and dominance outside of spawning aggregations. The behavioral paradigm described here is a key advance that will enable mechanistic studies of this complex sex change process.
PLoS ONE 01/2011; 6(5):e19576. · 4.09 Impact Factor
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ABSTRACT: In fishes, insulin-like growth factor-I (IGF-I) stimulates growth and differentiation but also plays a role in a number of other processes including osmoregulation, metabolism, immune response and reproduction. This study presents the cDNA encoding multiple prepro-IGF-I transcripts obtained from red drum, Sciaenopsocellatus, and examines differential expression in select adult tissues and during ontogeny. Four distinct transcripts were sequenced which were identical in the coding region for the signal (132 bp) and mature (204 bp) peptides but differed in the coding region of the E peptide by the exclusion of 117 (Ea-1), 81 (Ea-2) or 36 (Ea-3) bp compared to the 222 bp present in Ea-4. Analysis of the pertinent portion of the genomic sequence of this gene suggests that the transcripts are a result of alternative splicing. This is the first report of the expression of all four known prepro-IGF-I transcripts in a teleost other than a salmonid. The deduced amino acid sequences exhibited 70-95% identity with teleosts and somewhat lower identity to other vertebrates (60-75%). Three of the 4 transcripts (Ea-2, Ea-3, Ea-4) were expressed in the liver, ovary, spleen, gall bladder, brain, red muscle, pancreas and spinal cord of adults. Only the Ea-4 transcript was expressed in adult stomach tissue while no signal was detected in pituitary, retina, intestine, adipose or white muscle. In contrast, all 4 transcripts were expressed throughout ontogeny. The apparent expression of the Ea-1 transcript only during the larval stage may indicate a developmental role for this E peptide in red drum.
General and Comparative Endocrinology 10/2010; 169(1):75-81. · 3.27 Impact Factor
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ABSTRACT: The current study sought to clarify the role of cholecystokinin (CCK) in the digestion of larval red drum (Sciaenops ocellatus) in order to better characterize the processes limiting the utilization of microparticulate diets at first feeding. The red drum CCK cDNA, isolated from adult anterior intestine and pyloric caeca, contains a 414 base pair (bp) open reading frame encoding a deduced amino acid sequence of 138 residues which is highly similar to preprocholecystokinin from other vertebrates. The mature CCK octapeptide has the same amino acid sequence as that found in mammals and in Atlantic herring (Clupea harengus). Tissue distribution analysis of adult and juvenile red drum using primers specific for red drum CCK mRNA revealed bright bands in samples from the brain, pyloric caeca, anterior intestine, and gonad with fainter bands seen in all other tissues. Immunohistochemical analysis of larval red drum showed that CCK-immunoreactive (CCK-IR) cells were present as early as 3 days post hatch (DPH) in some fish and were present in all fish by 6 DPH. CCK-IR cells were found in the anterior midgut in early larvae and had spread to the first bend of the gut by day 6. In older larvae (18+ DPH), CCK-IR cells were found in large numbers in the anterior intestine and in the developing pyloric caeca. The sequence and distribution of CCK mRNA along with the presence of CCK-IR cells in early red drum larvae suggest that CCK is present and may be capable of regulating pancreatic secretion in early red drum larvae.
General and Comparative Endocrinology 11/2009; 166(1):152-9. · 3.27 Impact Factor
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ABSTRACT: Although cortisol plays an important role in teleost development, the onset of cortisol production and the cortisol stress response in teleosts remain poorly understood. Here we have reported basal cortisol levels and the development of the cortisol stress response in larval red drum (Sciaenops ocellatus). We isolated partial nucleic acid sequences encoding two key corticosteroidogenic enzymes, CYP11B and CYP21 and assessed ontogenetic patterns of their mRNA levels relative to basal and stress-induced cortisol production. Basal cortisol was first detected 3 days post-hatch (DPH) and reached a maximum at 9 DPH. Cortisol did not increase in response to an acute stressor prior to 6 DPH. From 6 DPH forward, stress caused significant increases in larval cortisol content. Stress-induced cortisol levels in 6-9 DPH larvae were highest 1h post-stress. In larvae 11 DPH and older, the highest cortisol measurements occurred 0.5h post-stress. Elevated cortisol was still evident after 3h in 6 DPH larvae. From 11 DPH onward, basal cortisol levels were reestablished in larvae by 1h post-stress. CYP11B and CYP21 transcripts were detected in red drum 12h prior to hatching and in all post-hatch larvae examined. Changes in CYP11B and CYP21 mRNA levels did not occur in association with the ontogenetic appearance of cortisol, or the onset of the stress response. As larvae developed, the dynamics of the cortisol stress response matured from a low magnitude, slow recovery response, to a response similar to that observed in juvenile and adult fish.
General and Comparative Endocrinology 08/2009; 165(2):269-76. · 3.27 Impact Factor
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ABSTRACT: There is considerable interest in rearing Southern flounder, Paralichthys lethostigma, for commercial production
and for stock enhancement. Both goals depend upon excellent larval nutrition for the production of
robust juveniles. The current use of live prey for larviculture is an expensive and time consuming process
that can be alleviated by weaning larvae onto dry feed. A study was conducted to assess the potential
for early weaning of southern flounder larvae onto a microdiet (MD). In addition, the activity of selected
digestive enzymes was measured during ontogeny to evaluate the digestive capabilities of the larvae over
time. Pancreatic enzyme activities (U larva−1) were very low or undetectable at hatching and a marked
increase in activity was not observed until the larvae reached 4 mm (~11 dph) in standard length for chymotrypsin
(24–44,000) and 6 mm (~25 dph) for amylase (b1–24), trypsin (1–18) and bile salt-dependent lipase
(0–443). Acid protease activity (~1.0) was detected once the larvae were 8.5–9.0 mm (37–39 dph) in length
although a sizeable increase in activity (N10.0) was not observed until after completemetamorphosis (N11.0 mm;
40–45 dph). Feeding regimes employed for the weaning study consisted of a live feed control (C) and a combination
of live feed and MD in which the addition of the MD was initiated on 11 dph and live feed terminated
on 17 (T17), 23 (T23) or 29 (T29) dph. At the end of the study (35 dph), mean standard length and the percent
of settled fish were significantly greater for fish in the control treatment (8.3 mm; 21.1%) than for fish fed any
combination of live prey and MD (6.4 mm; 2.0%). Average survival was 27.7% and no significant differences
were noted among treatments. However, the number of fish exhibiting spinal deformities, lordosis, was
significantly lower in the control and T29 treatments (1.7%) than the T17 and T23 treatments (25%). The results
of this study indicate that southern flounder larvae readily wean onto dry feed prior to the onset of metamorphosis.
However, decreased growth and a high incidence of lordosis emphasize the need for the development
of a more appropriate MD for this species when digestive enzyme activities are relatively low and
gastric digestion is absent.
Aquaculture 01/2009; 296:213-218. · 2.04 Impact Factor
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ABSTRACT: This study examined the fatty acid composition of cobia Rachycentron canadum eggs and yolksac larvae, as well as the ovaries of wild caught females as an initial guide to lipid nutritional requirements. A 2-wk feeding study also was conducted to investigate the effectiveness of four dietary treatments on the growth and survival of cobia larvae. Cobia eggs in the tailbud stage contained 31.4 ± 1.3 μg lipid/egg. After hatching, the amount of lipid decreased significantly (P < 0.05) from 28.3 ± 0.3 to 23.2 ± 0.1 μg lipid/larvae during the yolksac larval stage (days 1 to 3 after hatching). Ovaries from wild caught adults and captive spawned eggs and yolksac larvae contained high levels of PUFAs with docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA) accounting for approximately 80% of the total suggesting that cobia larvae may have a high dietary requirement for these fatty acids. For the feeding study, larvae were fed: 1) Artemia only; 2) enriched rotifers for 1 d only + microparticulate diet (day 313); 3) enriched rotifers for 3 d (day 3–5) + Artemia (day 3–13); and 4) enriched rotifers for 6 d (day 3–8) + Artemia (day 3–13). Cobia larvae began feeding on rotifers 3 d after hatching and on newly hatched Artemia nauplii by the fifth day following the onset of exogenous feeding (day 7). On day 7, no differences in larval growth were found among larvae fed rotifers for 3 versus 6 d, whereas larvae fed only Artemia or rotifers for I d followed by microparticulate diet were significantly smaller (P < 0.05) and did not survive beyond day 9 and 13, respectively. The results of the feeding study indicate that cobia larvae require rotifers for a minimum of 4 d following the onset of exogenous feeding.
Journal of the World Aquaculture Society 04/2007; 34(3):368 - 378. · 0.71 Impact Factor
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ABSTRACT: The cDNAs of the G protein-coupled receptor 54 (GPR54) and three prepro-gonadotropin-releasing hormones, GnRH-I (seabream GnRH), GnRH-II (chicken GnRH-II), and GnRH-III (salmon GnRH) were isolated and cloned from the brain of the teleost fish cobia, Rachycentron canadum. The cobia GPR54 cDNA was 95 and 51-56% identical to those of tilapia and mammalian models respectively. The GnRH cDNA sequences of cobia showed strong identities to those of tilapia, Atlantic croaker, red drum, and the seabass and seabream species. The real-time quantitative RT-PCR methods allowed detection of all three GnRH mRNAs on the first day after hatching (DAH). The GnRH-I mRNA levels, which were the lowest among the three GnRHs, increased gradually with two distinct peaks in larvae at 3 and 4 DAH. On the other hand, GnRH-II and GnRH-III mRNAs were significantly higher in larvae at 2 and 6 DAH compared with those on the preceding days. In addition, significant peaks of all the three GnRH mRNAs were observed in the brains of 26-day-old fish. The finding of higher GnRH-I and GnRH-II mRNAs in males than females at 153 DAH may be related to early puberty observed during the first year in laboratory-reared male cobia. Moreover, this study demonstrates for the first time the expression of GPR54 mRNA during larval development in a vertebrate species. The concomitant expression patterns of GPR54 and GnRH mRNAs during different stages of larval and juvenile developments, and during early puberty in male cobia suggest a potential relationship between GPR54 and multiple GnRHs during these stages of development consistent with the role of GPR54 in controlling GnRH release in mammals. The increase in GPR54 and GnRH mRNAs observed during early puberty in cobia is consistent with a similar change reported in pubertal rats. This finding together with the localization of GPR54 mRNAs on GnRH neurons in fish and mammals suggests that the GPR54-GnRH interactions may be conserved in different vertebrate groups.
Journal of Molecular Endocrinology 03/2007; 38(1-2):235-44. · 3.48 Impact Factor
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ABSTRACT: Cobia Rachycentron canadum is a fast-growing, pelagic marine species that has recently attracted aquaculturists in both the research and commercial sectors. The typical method of grow-out for this species is in outdoor systems where production is limited to locations and seasons conducive for adequate growth and survival. Expanding the culture of cobia to indoor recirculating aquaculture systems (RAS) would allow for the production of fingerlings throughout the year and extend production to cooler regions. Two rearing trials were conducted to examine the growth and survival of cobia from hatching through 4 (trial 1, T1) or 35 (trial 2, T2) g in RAS. Cobia larvae were reared in circular tanks placed in a raceway to control water temperature and quality. During early juvenile grow-out, fish were transferred without grading to a second raceway on 29 dph (T1) or over a period of grading from 29–43 dph (T2). Larval growth (1–22 dph) measured as standard length was similar for both trials ranging from∼3.9 to 14.7mm. However, larval growth measured as wet weight (0.033 g, T1; 0.026 g, T2) or dry weight (5.7 mg, T1; 3.9 mg, T2) was significantly greater on 22 dph during T1 as was the ratio between myotome height and standard length. These differences may have resulted from an increase in initial densities from 8.7 larvae l−1 (T1) to 14.7 larvae l−1 (T2) which apparently caused an increase in food competition and overall aggression. During juvenile growout, cobia reached 4.0 g on 43 dph in T1 and 35.4 g on 71 dph in T2matching weights achieved during grow-out in outdoor ponds. Over the course of both trials, survival was similar to that reported in outdoor ponds. Mean survival (±S.D.) during the early rearing phase (hatching through 29 or 43 dph) averaged 13.2±3.2%and 10.4±3.2%corresponding to final densities of 0.9±0.2 and 1.2±0.4 fish/l for T1 and T2, respectively. During the first grow-out phase (29–43 dph), survival of fish moved into the open raceway was 64.5%in T1 and 88.7% in T2. Survival of cobia during the second grow-out phase (43–71 dph) for T2 was 92.5%. The results of this study indicate thatcobia can be successfully cultured in indoor systems from hatching through at least 35 g without negatively affecting growth or survival.
Aquaculture 01/2007; 270:149-157. · 2.04 Impact Factor
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ABSTRACT: Cobia Rachycentron canadum is a migratory, pelagic species found in
warm marine waters worldwide, except for the central and eastern Pacific.
Considered uncommon throughout its range, cobia are not caught in quantities
that support a major commercial fishery in the U.S. and are often taken
incidentally while targeting other species. Cobia’s rapid growth rate and good
flesh quality have stimulated research with this species and aquaculture
production has increased annually since the late 1990’s. Researchers at the
University of Texas at Austin Marine Science Institute’s Fisheries and
Mariculture Laboratory (UT-FAML) have maintained cobia since 1991 in an
effort to learn about the general husbandry, spawning, and larval rearing of this
species. Since April 2001, both wild-caught and F1 cobia broodstock have
been induced to spawn naturally (without hormones) 39 times resulting in the
production of more than 45 million eggs to date. We spawned cobia for the last
five years in recirculating tank systems (25-42 m3) with and without heat pumps
to control water temperature. Spawning was induced under ambient or photothermal
controlled conditions resulting in spawns from March to December.
Offspring have been used to carry out numerous studies resulting in
publications addressing larviculture, feeding protocols, rearing density, salinity
tolerance, digestive system development, and studies of the neuronal control of
spawning.
01/2007: pages 45-56;
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ABSTRACT: Red drum settle into shallow seagrass meadows during the larval stage. Day-night cycles in these habitats result in marked diel temperature and dissolved oxygen (DO) cycles, and it is possible that extreme fluctuations influence endocrine development and growth of larvae. Here, we described red drum interrenal and thyroid ontogeny and determine responses to environmental stimuli with special emphasis on settlement to explore possible role of hormones as mediator of directive environmental factors. This study detected an early activation of thyroid and interrenal axis during the yolk-sac phase and a second activation of the thyroid starting at settlement size to the end of the larval period. Whole-body l-thyroxine (T4) and 3-5-3'-triiodo-l-thyronine (T3) showed a sharp decline at the juvenile stage. In contrast, cortisol steadily declines during the larval phase to a minimum before the end of the larval period. Older settlement-size larvae exposed to a strong stimulus increased whole body cortisol. In contrast, new settlers showed a minor cortisol rise suggesting changes on stress responsiveness during the ontogeny of the species. Additionally, settlement-size larvae exposed to various environmentally realistic temperature or DO fluctuations showed no difference in growth compared to fish grown under stable conditions (control). However, growth rate was significantly reduced in DO cycled fish with prolonged exposure to hypoxia. No differences were found in whole-body cortisol levels in the reduced growth treatment groups, suggesting that growth retardation was not related to a cortisol-mediated stress response. In moderate DO and temperature treatment groups, cortisol showed wider fluctuations than control groups during the night time that were not related to stress.
General and Comparative Endocrinology 05/2006; 146(2):108-18. · 3.27 Impact Factor
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Journal of the World Aquaculture Society 01/2006; 37:126-131. · 0.71 Impact Factor
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ABSTRACT: The purpose of this study was to examine the effect of varying dietary levels of highly unsaturated
fatty acids (HUFA) in live prey on the standard length, specific growth rate, survival, and fatty acid
composition of yellowtail snapper Ocyurus chrysurus larvae. Two experiments were conducted
utilizing rotifers and Artemia enriched with live algae (Isochrysis galbana or Nannochloris oculata) or
commercial preparations (Aquagrow Advantage, Aquagrow Advantage plus Aquagrow arachidonic
acid, and Algamac 2000). Larval growth and fatty acid composition were evaluated during the
rotifer, Brachionus plicatilis, and Artemia feeding periods and survival rates were calculated at the
termination of each trial (18 or 20 d after hatching). In general, prey enriched with the commercial
products contained higher levels of docosahexaenoic acid, eicosapentaenoic acid, n–3 HUFA, and
Σ HUFA than those enriched with live algae. The addition of arachidonic acid to the Aquagrow
Advantage enrichment medium significantly increased the amount of this fatty acid in rotifers but
not in Artemia. At the end of the growth trials, larval standard length was highest when larvae
were fed prey enriched with I. galbana (6.4 mm) or commercial preparations (6.7–7.1 mm) versus
N. oculata (5.2 mm). Furthermore, larvae fed prey enriched with commercial preparations had
significantly (P < 0.05) higher survival rates (2.2–5.9%) than those fed prey enriched with live algae
(1.1–1.4%). These results suggest that yellowtail snapper larvae require dietary levels of HUFA
beyond those achieved by enriching prey with live N. oculata or I. galbana.
Journal of the World Aquaculture Society 01/2005; 36:271-281. · 0.71 Impact Factor
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Journal of Experimental Marine Biology and Ecology 01/2002; 272:147-158. · 1.88 Impact Factor
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ABSTRACT: Cobia Rachycentron canadum is a marine finfish species with emerging global potential for mariculture. Positive culture attributes include capacity for natural and induced tank spawning, growth rates in excess of 6 kg/year, high disease resistance, high survival rates (post-larviculture stage) in tanks and net pens, adaptability to commercially available extruded diets, and high-quality fillets suitable for the sashimi as well as white tablecloth restaurant markets. Nonetheless, cobia production faces several bottlenecks limiting industrial expansion including limitations in fingerling production per unit volume. This paper will provide an overview of production limitations, and focus on recent spawning and larviculture research results and ongoing research initiatives.
Aquaculture.
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ABSTRACT: Cobia Rachycentron canadum has recently been recognized as a potential candidate for aquaculture because this species exhibits high growth rates during the larval and juvenile stages. A series of salinity tolerance tests were performed on larval cobia in order to identify the salinity requirements of this species during culture. The effect of spawning salinity on larval tolerance is also discussed. The 18-h survival of cobia larvae 3, 5, 7 and 9 days post-hatch (dph) following abrupt transfer to salinities ranging from 4 to 48 ppt was evaluated using logistic regression. The salinity range within which 90% of the larvae would be expected to survive appeared to be age-dependent and was narrowest at 3 dph (20.1–35.6 ppt) and wider at 7 and 9 dph (7.5–32.8 ppt). The 18-h tolerance of larvae to abrupt changes in salinity was unaltered by spawning salinities of 28.0 and 36.5 ppt. In the second part of the study, rearing salinities were dropped by 5 ppt day − 1 from 32–34 ppt (control) to 5, 10, 15 and/or 20 ppt beginning on 1, 4, 7, 10 or 13 dph. Larval survival from hatching through 10 days following the initial drop in salinity was significantly (P b 0.05) lower (b 2%) in the low salinity treatments than the control (12–15%) when the salinity drop was initiated 1 and 4 dph. No significant differences in larval survival were detected between the control (12.5%) and 20 ppt treatment (8.9%) when the salinity drop began on 7 dph but survival in the 10 ppt treatment (3.2%) was significantly lower than the control. When the salinity drop was initiated on 10 dph, no significant differences in survival (10.7–14.7%) were detected among treatments. Finally, no significant differences in survival (9.6–15.4%) were found when the salinity drop was initiated 13 dph and terminated 22 dph. However, when a similar study was extended to 28 dph survival from 13 to 28 dph was significantly lower in the 5 (49.4%) and 10 (72.5%) ppt treatments than the control (96.5%) due to disease. No significant differences in standard length were observed for larvae within each experiment irrespective of rearing salinity. The results of this study indicate that rearing cobia larvae in salinities as low as 15 ppt may be possible beginning 13 dph.
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ABSTRACT: Cobia (Rachycentron canadum) is an excellent aquaculture candidate and culture of this species continues to develop worldwide. Current culture practices generally include larviculture and production of early juveniles on land with final growout occurring in ocean cages. Data indicate that production and/or growout of juveniles in land based recirculating systems may be hampered by growth depression in fish held at even relatively low densities. The current study investigated the responses of early cobia juveniles cultured at three different stocking densities (0.04, 0.22, and 0.44 g of fish/L) over a 10-week period in a recirculating aquaculture system. Water temperature was maintained at 27 ± 1 C and salinity was 32.0 ± 3.0 ppt. Fluorescent light banks were used to maintain a light/dark cycle of 14 h light/10 h dark. Early juveniles used in this trial had an average initial weight of 6.7 ± 0.2 g and were stocked at 3, 10, or 20 per tank in order to reach target stocking densities. Fish were fed to satiation twice daily with a commercial diet and the amount fed was measured to determine feed efficiency. Fish from each tank were counted and weighed collectively each week until the end of the trial to monitor growth and survival. In addition, fish from the control (0.04 g/L) tanks were individually marked via clipping of the pectoral fins and weighed individually each week. Survival was high (≥ 96% in all treatments) and there were no significant differences among treatments. Growth was also not significantly different among treatments with weight gains between 2523 and 2747% of initial weight (SGR ranging from 5.18 to 5.29). Feed efficiency of the control (0.96 ± 0.02) was significantly lower than that of the 0.22 g/L treatment (1.04 ± 0.03).
Aquaculture. 264:223-227.
