Fundamentals of Aquatic Veterinary Medicine. Группа авторов

to play a role in aquatic species mortality through gill damage (Dorantes‐Aranda, 2015; Hallegraeff et al., 2017). Studies performed by Hallegraeff show that reactive oxygen species do not cause damage to fish independently, but when free fatty acids are present they work in synergy to increase the potency of the fatty acid. This results in damage to the gills and to osmoregulation. Microalgal blooms such as barbed diatoms can also cause damage to the gills through mechanical stress by lodging in fish gills (Hallegraeff et al., 2017).

      There is no effective treatment for the toxicity that occurs due to harmful algal blooms. Avoidance of the blooms is best achieved by decreasing runoff of high nutrient materials, planting grasses and other plants near waterways to help reduce nutrient runoff and use the nutrients in the water, and careful monitoring. If a large bloom occurs in an aquaculture facility, there are several considerations that need to be made before action is taken:

       Is the toxin present a danger to humans, aquatic species, or both?

       Is an early harvest an option?

       Will killing the algae cause more toxin to be suddenly released?

      With blooms that are specifically ichthyotoxic due to fatty acids and reactive oxygen species, the fish may still be safe for harvest. If so, it is important to prevent histamine build‐up by keeping the fish alive long enough to allow the system to be flushed. This can be accomplished by airlift upwelling and targeted clay applications to remove the ichthyotoxins (such as bentonite clay at 0.05–0.25 g/l for Prymnesium, Karenia, Karlodinium, Chattonella, Heterosigma, and Alexandrium). The last three listed have a lower removal percentage then the first three (Hallegraeff et al., 2017). If an early harvest is not an option, then means for movement of the fish and decreased nutrient load should be considered. The feed should be stopped to decrease nutrient levels. Cages can be moved to unaffected areas if possible. To reduce concentration, surrounding the fish with perimeter skirts and increased aeration or airlift upwelling can be used. Clay flocculation should be carefully considered based on the area the fish are in and the type of algal blooms present. Most clays can cause damage to benthic fauna present, especially mollusks (Hallegraeff et al., 2017)

      1.6 Diseases Associated with Suboptimal Water Quality

Many diseases or conditions have been wholly, or in part, associated with suboptimal water quality. Examples may be found in Chapter 4.

      Supplementary materials available online

       Bibliographic references.

       Further Resources.

References

      1 American Public Health Association, American Water Works Association, Water Environment Federation. (2017). Standard Methods for the Examination of Water and Wastewater, 23e. Baltimore, MD: American Public Health Association, American Water Works Association, Water Environment Federation.

      2 Anderson, D.M., Cembella, A.D. and Hallegraeff, G.M. (2012). Progress in understanding harmful algal blooms: paradigm shifts and new technologies for research, monitoring, and management. Annual Review of Marine Science 4: 143–176.

      3 Authman, M.M. (2015). Use of fish as bio‐indicator of the effects of heavy metals pollution. Journal of Aquaculture Research and Development 6(4). doi:10.4172/2155‐9546.1000328.

      4 Bartucca, M., Mimmo, T., Cesco, S. et al. (2016). Nitrate removal from polluted water by using vegetated floating system. Science of the Total Environment 542: 803–808.

      5 Clean Water Team. (2002). Electrical Conductivity/Salinity Fact Sheet. Fact Sheet 3.1.3.0. Clean Water Team Guidance Compendium for Watershed Monitoring and Assessment State Water Resources Control Board, Version 2.0. Sacramento, CA: California State Water Resources Control Board.

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