Harbor Branch Oceanographic Institute Foundation, Inc. (FL)

Less than 10 aquaculture farms in the U.S. have been successful in commercially raising and distributing the popular Florida pompano fish. A new study has determined the optimal salinity required to culture fingerlings (juvenile fish) from hatch to weaning under on-farm conditions. Researchers have shown it's possible to grow this warm water marine species in salinities a low as 10 parts per thousand, which makes it more economic and easier for producers far from the coast to attempt Florida pompano commercial growth. The Florida pompano, Trachinotus carolinus, a fish species that can live in waters of a wide range of salinity, is a prime candidate for aquaculture commercial fish production in the United States. Identified by its compressed silvery body with yellow dorsal and ventral surfaces, this species is found in warm water habitats along the eastern Atlantic Ocean. Florida pompano also is a popular target for recreational anglers along the U.S. Atlantic Coast from Massachusetts to Florida. There are less than 10 aquaculture farms across the U.S. that have been successful in commercially raising and distributing Florida pompano. Many farms import their broodstock from countries such as Mexico, the Dominican Republic and Brazil. When attempting to rear Florida pompano from hatch to market, farms face a variety of challenges including access to seawater. On inland farms, seawater must be mixed on-site using artificial sea salt products, which can contribute to high production costs and lower profit returns. While several studies have investigated using juvenile Florida pompano in low salinity, no low salinity experiments have been conducted on Florida pompano larvae (early stages of a fish). To address the knowledge gaps of the impact of low salinity on Florida pompano larval health, researchers from Florida Atlantic University's Harbor Branch Oceanographic Institute, in collaboration with two local fish farms, Live Advantage Baits and Proaquatix, conducted a novel experiment that serves as a model study for future on-farm collaborations and helps build a bridge between scientists and farmers in aquaculture. The objective of the study was to determine the optimal salinity required to culture fingerlings (juvenile fish) from hatch to weaning under on-farm conditions. Low salinity conditions can affect the early development of the Florida pompano by increasing osmoregulatory stress, which reduces the availability of metabolic energy reserves, otherwise needed for developmental processes such as cellular formation. For the study, Florida pompano larvae were reared in three different salinities: 10, 20 and 30 parts per thousand (ppt) at local producers' farms. Growth, fatty acid profiles and transcriptome responses (cellular formation) were quantified every three days after hatching (three, six, nine, 12, 15, 18 and 24 days post hatch) and results were compared across salinities. Results, published in the journal Aquaculture, showed that larvae reared at 10 ppt grew at a normal rate and the developmental stage had a greater impact than salinity on fatty acid composition and larval gene expression. "We have shown that it is possible to grow this warm water marine species in salinities a low as 10 parts per thousand, which makes it more economic and easier for producers far from the coast to attempt Florida pompano commercial growth," said Sahar Mejri, Ph.D., senior author and an assistant research professor, Department of Aquaculture and Stock Enhancement at FAU Harbor Branch. "We expect to run this study for a longer period to investigate the long-term effects of low salinity on larval health and development." An important metric for determining the health and viability of Florida pompano as a commercial food species is the lipid pro the larvae. Lipids are composed of individual fatty acids, including essential fatty acids (EFAs) such as docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA). In the early days of development, the fatty acids linoleic acid (LA), alpha linoleic acid (LNA), and 18:3 n-6 were proven to be important as potential energy fuels and precursors for long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis, which was supported by the whole transcriptomics analysis. "Larvae reared at the lowest salinity, 10 parts per thousand, seemed healthy and showed normal growth and physiological development overall with no adverse effects," said Mejri. "Larval diets combined with developmental stages had a greater impact than salinity on fatty acid composition and transcriptomics gene expression." Study co-authors are David J. Bradshaw II, Ph.D., a senior research fellow; Victoria Uribe, an aquaculture research technician; Laura E. King, a Ph.D. student; Carlie S. Perricone, a research coordinator; Gonzalo Illán, Ph.D., a post-doctoral fellow; Marty Riche, Ph.D., a research professor; and Paul S. Wills, Ph.D., a research professor and associate director for research, all with FAU Harbor Branch; and Elizabeth Allmon, Ph.D., a post-doctoral research scientist; and Marisol Sepulveda, Ph.D., a professor, both with Purdue University. This work was supported by the U.S. Department of Agriculture, Agricultural Research Service (cooperative agreement number 59-6034-9-007).

The Indian River Lagoon (IRL) is a bull shark nursery habitat crucial to survival and recruitment of Atlantic coast bull sharks. Analysis of 123 samples found the presence of one or more phycotoxin from harmful algal blooms in 82 percent of the bull sharks and their prey items. Findings highlight the potential threat of toxic algae to the IRL's ecosystem and surrounding human populations that may consume the same prey species. The highest concentrations of most toxins were detected in gut content samples, highlighting dietary exposure as an important mechanism of toxin transfer to bull sharks in the system. Stretching 251 kilometers along Florida's East Coast, the Indian River Lagoon has experienced large-scale, frequent blooms of toxic harmful algae in recent decades. Harmful algal blooms (HABs) occur when an overgrowth of aquatic microalgae over-accumulate in a body of water, negatively affecting wildlife and humans and degrading aquatic habitats. HAB species produce phycotoxins, potent chemicals produced by photosynthetic organisms, which can move through multiple levels of aquatic food webs as they accumulate and are transferred from prey to predator. Sentinel, or indicator, species can provide an integrated picture of contaminants in the environment. Researchers from Florida Atlantic University's Harbor Branch Oceanographic Institute, in collaboration with the Florida Institute of Technology and the University of Connecticut, are the first to measure multiple phycotoxin concentrations in bull sharks (Carcharhinus leucas) in the Indian River Lagoon, an estuary of national significance. In a prior study, the FAU Harbor Branch researchers confirmed the value of the Indian River Lagoon as a bull shark nursery habitat crucial to survival and recruitment of Atlantic coast bull sharks. In recent decades, human water pollution has compromised the biological integrity of the lagoon, which may continue to degrade if environmental pollution in the area continues. For the current study, researchers measured concentrations of phycotoxins in samples collected from 50 immature (young) bull sharks captured in the Indian River Lagoon between 2018 and 2020. They used ultra-performance liquid chromatography/tandem mass spectrometry to measure the toxins in shark gut contents, plasma (blood) and liver. Results, published in the journal Science of the Total Environment, suggest multiple phycotoxins in the Indian River Lagoon are widespread or persistent in the environment. Analysis of 123 samples demonstrated the presence of multiple phycotoxins (microcystin, nodularin, teleocidin, cylindrospermopsin, domoic acid, okadaic acid and brevetoxin) in sampled bull sharks. The highest concentrations of most toxins were detected in gut content samples, highlighting dietary exposure as an important mechanism of toxin transfer to bull sharks in the system. "The presence of one or more phycotoxin in 82 percent of the bull sharks sampled in our study and their prey items highlights the potential threat of toxic algae to the Indian River Lagoon ecosystem and surrounding human populations that may consume the same prey species," said Michelle L. Edwards, corresponding author, former field technician and marine science and oceanography graduate student at FAU Harbor Branch. Other than brevetoxin, all of the detected toxins (microcystin, nodularin, teleocidin, cylindrospermopsin, domoic acid, okadaic acid) were present in plasma samples. "Due to their ecology within the Indian River Lagoon, including residence during early life stages and use of distinct regional areas, bull sharks in the system served as an appropriate sentinel species to survey toxins," said Matt Ajemian, Ph.D., senior author, an assistant research professor and director of The Fish Ecology and Conservation Lab at FAU Harbor Branch. "In addition, the integrative nature of using gut contents of an upper-level predator for assessment of toxin presence, allowed us to identify toxins in several lower trophic species, including stingrays, catfishes and mullet." One important vector species for the transfer of phycotoxins to bull sharks in the Indian River Lagoon was the most commonly identifiable prey item in the study: mullet. In fact, 60 percent of gut contents in which microcystin was identified contained mullet. "Mullet are distributed throughout the Indian River Lagoon and migrate to offshore areas to spawn between September and December each year, a similar pattern to seasonal offshore movements by young bull sharks that spend time in offshore areas between October and March each year," said Edwards. Most toxins were detected in samples collected from all three regions of the Indian River Lagoon (North, Central, South) and during both "wet" and "dry" seasons despite the tendency of resident bull sharks to spend most of their time in specific regions with varied seasonal area usage such as offshore area movements. "Many phycotoxins can remain in the environment after a harmful algal bloom period ends," said Ajemian. "Both microcystin and domoic acid, an acid-type neurotoxin, which was the most commonly detected toxin we found in the bull sharks in our study, can adsorb to sediments and could be ingested by benthic organisms or become resuspended in the water column. This makes tracing the timing of exposure to these toxins a tremendous challenge." The higher concentrations in gut contents compared to other tissues of the shark suggest that although Indian River Lagoon-resident bull sharks may be frequently exposed to phycotoxins, they may not accumulate them compared to lower trophic species. "Research on the potential for accumulation in other shark tissues not sampled in our study may be warranted," said Edwards. According to Ajemian, they have just scratched the surface on what HAB exposure means for bull sharks in the Indian River Lagoon. "This was an essential first step in developing critical baselines as we continue to monitor the responses of these animals to HABs in the future," said Ajemian. Study co-authors are Adam M. Schaefer, Abt Associates; Malcolm McFarland, Ph.D., an assistant research professor, FAU Harbor Branch; Spencer Fire, Ph.D., an associate professor, Florida Institute of Technology; and Christopher R. Perkins, Ph.D., environmental laboratory director, University of Connecticut. This work was supported by the Disney Conservation Fund, SeaWorld and Busch Gardens Conservation Fund, the Harbor Branch Oceanographic Institute Foundation, and Florida Center for Coastal and Human Health. Edwards was additionally supported by the Sunrise Rotary Club of Vero Beach.