WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2018 59 (CONTINUED ON PAGE 60) classes known, six divisions have species that produce toxic bioactive compounds (Table 1). The designation of freshwater or marine toxin occurrence is based on where the toxin was first identified and should not be construed as meaning that this is the sole location for that toxin. For instance, euglenophycin was first identified from a North Carolina aquaculture facility (Zimba et al. 2004), yet occurs widely in brackish to hypersaline rivers and streams (Zimba et al. 2017). Another example is the occurrence of the hepatotoxin microcystin in marine corals (Richardson et al. 2007), in marine shrimp aquaculture facilities (Zimba et al. 2006), and freshwater systems (Zimba et al. 2001). Algal Toxin Groups The cyanobacterial toxins are perhaps the most diverse of any HAB division, with over 65 different toxin classes produced that are classified into eight activity groups including hepatotoxins (3 classes), neurotoxins (9), cytotoxins (21), protease inhibitors (17), dermal toxins (2), grazing deterrents (4), molluscicides (5), anti-malaria compounds (6), and feeding deterrents (1). We have identified the production of over 11 bioactive compounds per cyanobacterial isolate in an analysis of 149 terrestrial, marine, and freshwater isolates. Micropeptin, a protease inhibitor, was the most common cyanotoxin group produced by species in this survey and accounted for over 41 percent of toxin occurrence. Little work has been done on estuarine benthic cyanobacteria in the United States but benthic communities in New Zealand and other countries have been prolific producers of bioactive metabolites. We recently identified one cryptic small cyanobacteria that produced anabaenopeptins responsible for mysid population declines and death, with two other new-to-science taxa implicated in redfish and shrimp mortalities. Dinophyceae occur widely in marine settings, with over 90 percent of the 2000 known species found in marine habitats. About Intensive aquaculture requires additional food resources to be added to ponds to increase primary and secondary production. The inherent efficiencies of feeding results in over half of the nitrogen being released to water and sediments through excretion, overfeeding, and feed sinking before consumption. These nutrients can increase dissolved nutrient concentrations and promote algal bloom development. While algal blooms are typically useful to decrease aeration requirements, on some occasions harmful algal species proliferate in ponds. These blooms can be either planktonic or benthic, the latter being sometimes difficult to recognize. A quick informed decision is critical for management of toxic harmful algal blooms (HABs) to prevent large financial losses. Testing of ponds suspected of harboring toxic algae can be approached as a sequence after recognition of a change in feeding or presence of unusual activity, including mortality. If toxic algae are suspected, pond algal composition needs to be determined. It is advisable to collect samples of windrowed sediments, including algae, to have a complete picture of potential toxic species present. Samples should be examined live if possible within a few hours of collection, or alternatively preserved with a compatible preservative, such as Lugol’s iodine, formalin or glutaraldehyde. Although microscopic identification can provide insights into potential algal toxins in ponds, the confirmatory step of analyzing samples from ponds is essential (Fig. 1) as not all members of a toxin-producing species actually produce toxins, i.e. the gene clusters responsible for toxin formation can be lost or modified. Two exceptions are the prymnesiophytes and raphidophytes; both appear to produce toxins in most if not all strains. Euglenophycin was found in 6 of 7 strains of Euglena sanguinea. Toxin production on a per cell basis can vary by >100-fold even in toxic strains. Harmful algal blooms can cause aquaculture mortalities by enhanced oxygen demand causing hypoxic/anoxic conditions and through secondary metabolite formation. Of the 13 algal A Review of Algal Toxin Effects on Freshwater and Marine Aquaculture Systems Paul V. Zimba and I-Shuo Huang Unusual feeding activity, weird swimming/activity, changes in water color/smell Identification of algae present in the water column and sediment to determine potentially toxic species present Analytical assessment of toxins present in water and in tissue using ELISA (presumptive) and MS/MS detection (confirmatory) FIGURE 1. Steps in identification of harmful algal bloom occurrence in aquaculture systems.
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