Fish are an important component of marine ecosystems, but relatively little is known of their health, in part because sick and dying fish are difficult to detect.
Since 2001, we have worked with the City and County of Honolulu to monitor fish at various sewer outfalls around Oahu for presence of liver tumors. As part of this process, we are keeping tabs on general health of fish by examining internal organs for presence of lesions that could aid in detecting shifts in health status over time. Part of these activities also involve disease outbreak investigations. For instance, we have documented tumors in various species of reef fish in the main and northwestern Hawaiian Islands.
Pufferfish Mortality Investigation
From June to October 2010, the HFS received reports of Stripebelly pufferfish either puffed up in the water, floating unable to submerge, or washed up on the beach. There were also reports of puffers biting each other and even attacking divers. At necropsy, fish had massively swollen livers and hyper-inflated gas bladders. A bit of collaborative sleuthing by HFS and the National Oceanic Atmospheric Administration’s Marine Products Chemistry laboratory in Charleston, SC revealed that the fish likely died from ingesting a natural toxin.
Microscopic examination of tissues suggested a poison (toxin) might be responsible. Laboratory tests revealed the presence of a small chemical compound in pufferfish tissues that was toxic to cells. We suspect that fish somehow ingested the toxin that led to liver failure and subsequent clinical signs seen in the field. As part of their defenses, numerous marine organisms make chemicals that are toxic when eaten. The most common examples are toxins produced by microscopic algae that bioaccumulate in fish or shellfish. We think the same thing happened to the pufferfish though the source of the toxin is not yet known. Pufferfish were seen dying in all the main Hawaiian Islands suggesting that the cause was geographically widespread (e.g. not likely something like point source pollution).
Surgeonfish die-off in the Northern Marianas
In early August 2014, there was a die-off of lined surgeonfish (known locally as Hiyok) that started on Tinian and spread to Saipan. It is estimated that hundreds of fish were found dead on various beaches during that time, and that the mortality was limited to blue-lined surgeonfish. Affected fish were noticed to exhibit lack of fear of humans, appeared drunk, and had a propensity to swim towards shallow water and upon reaching bottom, lose their righting reflex, and wash up on the beach. There was concern on the part of the community because the Hiyok is an important food fish, and the suitability of these fish for consumption was questioned. The mortality continued through September but appeared to wane at the end of September-early October. The HFS collaborated with CNMI Department of Fish & Wildlife who submitted fish samples for necropsy. Laboratory tests revealed that fish died from ingesting a natural toxin, probably produced by algae.
- Overview
Fish are an important component of marine ecosystems, but relatively little is known of their health, in part because sick and dying fish are difficult to detect.
Since 2001, we have worked with the City and County of Honolulu to monitor fish at various sewer outfalls around Oahu for presence of liver tumors. As part of this process, we are keeping tabs on general health of fish by examining internal organs for presence of lesions that could aid in detecting shifts in health status over time. Part of these activities also involve disease outbreak investigations. For instance, we have documented tumors in various species of reef fish in the main and northwestern Hawaiian Islands.
Pufferfish Mortality Investigation
Sources/Usage: Public Domain.Pufferfish. From June to October 2010, the HFS received reports of Stripebelly pufferfish either puffed up in the water, floating unable to submerge, or washed up on the beach. There were also reports of puffers biting each other and even attacking divers. At necropsy, fish had massively swollen livers and hyper-inflated gas bladders. A bit of collaborative sleuthing by HFS and the National Oceanic Atmospheric Administration’s Marine Products Chemistry laboratory in Charleston, SC revealed that the fish likely died from ingesting a natural toxin.
Microscopic examination of tissues suggested a poison (toxin) might be responsible. Laboratory tests revealed the presence of a small chemical compound in pufferfish tissues that was toxic to cells. We suspect that fish somehow ingested the toxin that led to liver failure and subsequent clinical signs seen in the field. As part of their defenses, numerous marine organisms make chemicals that are toxic when eaten. The most common examples are toxins produced by microscopic algae that bioaccumulate in fish or shellfish. We think the same thing happened to the pufferfish though the source of the toxin is not yet known. Pufferfish were seen dying in all the main Hawaiian Islands suggesting that the cause was geographically widespread (e.g. not likely something like point source pollution).
Surgeonfish die-off in the Northern Marianas
In early August 2014, there was a die-off of lined surgeonfish (known locally as Hiyok) that started on Tinian and spread to Saipan. It is estimated that hundreds of fish were found dead on various beaches during that time, and that the mortality was limited to blue-lined surgeonfish. Affected fish were noticed to exhibit lack of fear of humans, appeared drunk, and had a propensity to swim towards shallow water and upon reaching bottom, lose their righting reflex, and wash up on the beach. There was concern on the part of the community because the Hiyok is an important food fish, and the suitability of these fish for consumption was questioned. The mortality continued through September but appeared to wane at the end of September-early October. The HFS collaborated with CNMI Department of Fish & Wildlife who submitted fish samples for necropsy. Laboratory tests revealed that fish died from ingesting a natural toxin, probably produced by algae.
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