Environmentally conditioned, year‐round volitional spawning of cobia (Rachycentron canadum) in broodstock maturation systems

Year‐round control of the spawning cycle of cobia (Rachycentron canadum) has been established by using water temperature manipulation. To compare the effectiveness of using this method to induce volitional spawning in cobia, two 80 m3 recirculating aquaculture systems (RAS) were used. Temperatures in one of the maturation tanks (‘Mat 1’) were maintained between 27 and 29°C for 12 months of the 15.5‐month study period. Temperatures in the second maturation tank (‘Mat 2’) were allowed to fluctuate naturally throughout the year and ranged from 20 to 32°C. A total of 101 spawning events occurred in the tanks between the spring of 2008 and the summer of 2009 (3 April 2008 to 17 June 2009). Of the 38 total spawning events in Mat 1, 17 of them (44.7% of all Mat 1 spawning events) occurred during the off‐season (fall and winter). The egg viability rates did not differ significantly (P > 0.05) between on‐ and off‐season spawns in Mat 1. Conversely, cobia broodstock exposed to natural water temperatures (no environmental manipulation) in Mat 2 followed the natural pattern of warm water (>26°C) dependence, limiting egg production to spring and summer seasons. This method of water temperature manipulation allows for effective control of the cobia reproductive cycle without compromising egg viability

Effect of replacing darkness with dim light in the larviculture of red snapper, Lutjanus campechanus

Larviculture of red snapper was conducted using two lighting regimes to explore the effects of replacing periods of darkness with periods of light.•Extending exposure of red snapper larvae to dim light does not impact endpoints of growth, survival or feed consumption compared to a standard diel lighting strategy.•Replacing periods of darkness with dim light causes swim bladder inflation to occur more rapidly.•Reducing time of complete darkness may impact growth and feed consumption during development, but these changes do not persist after metamorphosis occurs.•The strategy of extending light exposure does not likely confer significant advantages in the large-scale production of red snapper fingerlings.Progress towards the development of reliable hatchery technology for red snapper, Lutjanus campechanus, has been limited by inconsistent spawning and difficulties in larval rearing. We report on recent progress to improve this technology. A larval rearing trial assessing the effects of two different photoperiods was conducted at the University of Miami Experimental Hatchery (UMEH). Four 400-L tanks were subjected to a photoperiod of 16 h of full spectrum light, and four 400-L tanks were subjected to 16 h of full spectrum light and 8 h of dim light through 11 days post hatch (dph). S-strain rotifers, Brachionus rotundiformis, were used as the exclusive first feeding source and were maintained at a density of 25 ml−1 throughout the experimental period. Standard length, swim bladder inflation, and feed consumption were measured for each tank at 3, 6, 9 and 12 dph. Survival was quantified at 12 dph and at the completion of weaning onto dry feeds at 40 dph. No significant differences in growth, feed consumption, or survival rates were observed between treatments at the conclusion of the trial. However, tanks exposed to a treatment involving 8 h of dim light showed completion of swim bladder inflation in 92.5 ± 10.8 % of larvae sampled by 9 dph, while tanks maintained with 16 h of light and 8 h of darkness showed a significant reduction with only 60 ± 2.5 % swim bladder inflation at this sample date (p = 0.0131). By 12 dph, all larvae in all tanks showed >95 % swim bladder inflation success. Total survival across treatment groups through 13 dph was 66 ± 8.0 % and 4.6 ± 1.0 % at 40 dph when the larvae were fully weaned onto dry diets

Advancements in hatchery production of red snapper Lutjanus campechanus: Exclusive use of small strain rotifers as initial prey for larval rearing

The red snapper (Lutjanus campechanus) has one of the most valued fisheries in the southeastern United States and has been largely studied for its aquaculture potential with varied results that revealed production challenges. This study focused on addressing challenges in larval rearing and juvenile production of this species. Broodstock fish were acclimated in a 60 m(3) tank equipped with recirculating aquaculture system (RAS) and temperature control. After 1 year in captivity, fish volitionally spawned and larval rearing trials were conducted in replicated flow-through seawater tanks ranging from 0.4 to 2.4 m(3), at a temperature range of 24-26 degrees C. Enriched s-strain rotifers, Brachionus rotundiformis (lorica length of 100-210 mu m), were used for first feeding. Enriched Artemia sp. were gradually introduced after 18 days post hatch (DPH). The survival rate before metamorphosis (12 DPH) averaged 66.09 +/- 0.08%. Survival rate from yolk-sac larvae to post-metamorphic early juvenile averaged 4.43 +/- 0.01%. At 40 DPH, early red snapper juveniles averaged 0.35 +/- 0.02 g in weight and 28.83 +/- 0.60 mm in standard length. A total of 31,849 fully weaned juveniles were harvested. This study demonstrates that small strain rotifers can be used exclusively as first feeding prey organism for red snapper larvae, representing a significant advancement for red snapper juvenile production

A novel system for embryo-larval toxicity testing of pelagic fish: Applications for impact assessment of Deepwater Horizon crude oil

Key differences in the developmental process of pelagic fish embryos, in comparison to embryos of standard test fish species, present challenges to obtaining sufficient control survival needed to successfully perform traditional toxicity testing bioassays. Many of these challenges relate to the change in buoyancy, from positive to negative, of pelagic fish embryos that occurs just prior to hatch. A novel exposure system, the pelagic embryo-larval exposure chamber (PELEC), has been developed to conduct successful bioassays on the early life stages (ELSs; embryos/larvae) of pelagic fish. Using this unique recirculating upwelling system, it was possible to significantly improve control survival in pelagic fish ELS bioassays compared to commonly used static exposure methods. Results demonstrate that control performance of mahi-mahi (Coryphaena hippurus) embryos in the PELEC system, measured as percent survival after 96-hrs, significantly outperformed agitated static exposure and static exposure systems. Similar significant improvements in 72-hr control survival were obtained with yellowfin tuna (Thunnus albacares). The PELEC system was subsequently used to test the effects of photo-induced toxicity of crude oil to mahi-mahi ELSs over the course of 96-hrs. Results indicate a greater than 9-fold increase in toxicity of Deepwater Horizon (DWH) crude oil during co-exposure to ambient sunlight compared to filtered ambient sunlight, revealing the importance of including natural sunlight in 96-hr DWH crude oil bioassays as well as the PELEC system's potential application in ecotoxicological assessments. Images and diagrams are from the corresponding author and shapes were created by the corresponding author using Microsoft PowerPoint. [Display omitted] •A novel exposure system for fish ELS toxicity testing (the PELEC) is reported.•The method improves ELS toxicity testing of high-value pelagic fish species.•Testing results indicate that mahi-mahi embryos are highly sensitive to PAHs.•The PELEC also allows for testing of photo-induced crude oil toxicity.•Natural sunlight co-exposure with DWH crude oil significantly increases toxicity

Remote Predictions of Mahi-Mahi (Coryphaena hippurus) Spawning in the Open Ocean Using Summarized Accelerometry Data

Identifying complex behaviors such as spawning and fine-scale activity is extremely challenging in highly migratory fish species and is becoming increasingly critical knowledge for fisheries management in a warming ocean. Habitat use and migratory pathways have been extensively studied in marine animals using pop-up satellite archival tags (PSATs), but high-frequency data collected on the reproductive and swimming behaviors of marine fishes has been limited by the inability to remotely transmit these large datasets. Here, we present the first application of remotely transmitted acceleration data to predict spawning and discover drivers of high activity in a wild and highly migratory pelagic fish, the mahi-mahi (Coryphaena hippurus). Spawning events were predicted to occur at nighttime, at a depth distinct from non-spawning periods, primarily between 27.5 and 30°C, and chiefly at the new moon phase in the lunar cycle. Moreover, throughout their large-scale migrations, mahi-mahi exhibited behavioral thermoregulation to remain largely between 27 and 28°C and reduced their relative activity at higher temperatures. These results show that unveiling fine-scale activity patterns are necessary to grasp the ecology of highly mobile species. Further, our study demonstrates that critical, and new, ecological information can be extracted from PSATs, greatly expanding their potential to study the reproductive behavior and population connectivity in highly migratory fishes

Brief Oil Exposure Reduces Fitness in Wild Gulf of Mexico Mahi-Mahi (Coryphaena hippurus)

The Deepwater Horizon (DWH) disaster released 3.19 million barrels of crude oil into the Gulf of Mexico (GOM) in 2010, overlapping the habitat of pelagic fish populations. Using mahi-mahi (Coryphaena hippurus)-a highly migratory marine teleost present in the GOM during the spill -as a model species, laboratory experiments demonstrate injuries to physiology and behavior following oil exposure. However, more than a decade postspill, impacts on wild populations remain unknown. To address this gap, we exposed wild mahi-mahi to crude oil or control conditions onboard a research vessel, collected fin clip samples, and tagged them with electronic tags prior to release into the GOM. We demonstrate profound effects on survival and reproduction in the wild. In addition to significant changes in gene expression profiles and predation mortality, we documented altered acceleration and habitat use in the first 8 days oil-exposed individuals were at liberty as well as a cessation of apparent spawning activity for at least 37 days. These data reveal that even a brief and low-dose exposure to crude oil impairs fitness in wild mahi-mahi. These findings offer new perspectives on the lasting impacts of the DWH blowout and provide insight about the impacts of future deep-sea oil spills.Superscript/Subscript Available</commen

Capture, transport, prophylaxis, acclimation, and continuous spawning of Mahi-mahi (Coryphaena hippurus) in captivity

Successful culture of marine fish relies upon availability of high quality fertilized eggs obtained from broodstock. However, some of the most critical aspects of obtaining such eggs are often overlooked. These aspects include the capture, transport, acclimation, and spawning of sexually mature wild-caught fish. Mahi-mahi (Coryphaena hippurus), also known as dolphinfish, have been identified as one of the most promising candidate species for development of warm-water marine finfish aquaculture due to their high growth rate, market presence, and global distribution. In addition, mahi-mahi have proven to be a useful model species for physiology and environmental toxicology research, specifically in studies examining tropical and subtropical pelagic teleosts. One of the keys to aquaculture development of this species is the ability to obtain year-round production of fertilized embryos. This study documents the technical methods utilized to reach a point of consistent mahi-mahi egg production year-round, while also detailing the live transport tank and land-based spawning tank design, implementation, and operation. Following three different groups of wild-caught mahi-mahi broodstock from the point of capture throughout their lifespan, this study provides novel information on growth, survival, and spawning of this species in captivity. Results from this research have allowed for significant new insights into the effects of a variety of environmental stressors on the early life stages of this species. Furthermore, the ability to maintain consistent spawning populations of mahi-mahi in captivity has allowed for reliable and consistent production of fully-weaned fingerlings of this species, thereby resolving one of the key industry bottlenecks that has been limiting expansion of mahi-mahi commercial-scale aquaculture. •Technical methods are reported for developing a mahi-mahi broodstock population.•Results of environmental and nutritional conditioning allow for year-round spawning.•Design of mahi-mahi live transport and recirculating maturation systems are reported.•Growth and food conversion of broodstock reveal novel information on mahi-mahi.•Unique methods presented in this study allow for high survival and reliable spawning of broodstock mahi-mahi