Fish mortality associated to volcanic eruptions in the Canary Islands

The Canary Islands are an active volcanic archipelago. In the last decade, volcanic activity has occurred twice on the youngest and western most islands: El Hierro (submarine eruption) in 2011-12, and La Palma (subaerial eruption) in 2021. 70 fish specimens of different species from El Hierro volcano and 14 from La Palma were necropsied. A notable high and early mortality of fishes was registered during the submarine eruption of El Hierro. In most of them, generalized congestion in the gills, liver, spleen, kidney, heart and rete mirabile of the swim bladder was observed. Some specimens also presented exophthalmia, gastric eversion, ocular haemorrhages, over-inflation of swim bladder and gas bubbles mainly on the skin and cornea. The eruption of La Palma volcano was characterized by the emission of large amounts of lava flows and pyroclastic deposits (mainly ash in size) both, on land and sea. Lava flowed on land and eventually reached the sea, forming lava deltas in the coastline of La Palma. This event was also associated with an increase in fish mortality in locations near to the lava deltas. Fishes presented ash particles in opercula/oral cavities and gills. In addition, several fishes presented an intense intestinal impaction composed of volcanic material including ashes and hyaloclastites fragments. To our best knowledge this study describes, for the first time, pathological findings in dead fishes associated with two different styles of recent volcanic eruptions in the Canary Islands

Establishment of a fish model to study gas-bubble lesions

Decompression sickness (DCS) is a clinical syndrome caused by the formation of systemic intravascular and extravascular gas bubbles. The presence of these bubbles in blood vessels is known as gas embolism. DCS has been described in humans and animals such as sea turtles and cetaceans. To delve deeper into DCS, experimental models in terrestrial mammals subjected to compression/decompression in a hyperbaric chamber have been used. Fish can suffer from gas bubble disease (GBD), characterized by the formation of intravascular and extravascular systemic gas bubbles, similarly to that observed in DCS. Given these similarities and the fact that fish develop this disease naturally in supersaturated water, they could be used as an alternative experimental model for the study of the pathophysiological aspect of gas bubbles. The objective of this study was to obtain a reproducible model for GBD in fish by an engineering system and a complete pathological study, validating this model for the study of the physiopathology of gas related lesions in DCS. A massive and severe GBD was achieved by exposing the fish for 18 h to TDG values of 162–163%, characterized by the presence of severe hemorrhages and the visualization of massive quantities of macroscopic and microscopic gas bubbles, systemically distributed, circulating through different large vessels of experimental fish. These pathological findings were the same as those described in small mammals for the study of explosive DCS by hyperbaric chamber, validating the translational usefulness of this first fish model to study the gas-bubbles lesions associated to DCS from a pathological standpoint

Decompressive Pathology in Cetaceans Based on an Experimental Pathological Model

Decompression sickness (DCS) is a widely known clinical syndrome in human medicine, mainly in divers, related to the formation of intravascular and extravascular gas bubbles. Gas embolism and decompression-like sickness have also been described in wild animals, such as cetaceans. It was hypothesized that adaptations to the marine environment protected them from DCS, but in 2003, decompression-like sickness was described for the first time in beaked whales, challenging this dogma. Since then, several episodes of mass strandings of beaked whales coincidental in time and space with naval maneuvers have been recorded and diagnosed with DCS. The diagnosis of human DCS is based on the presence of clinical symptoms and the detection of gas embolism by ultrasound, but in cetaceans, the diagnosis is limited to forensic investigations. For this reason, it is necessary to resort to experimental animal models to support the pathological diagnosis of DCS in cetaceans. The objective of this study is to validate the pathological results of cetaceans through an experimental rabbit model wherein a complete and detailed histopathological analysis was performed. Gross and histopathological results were very similar in the experimental animal model compared to stranded cetaceans with DCS, with the presence of gas embolism systemically distributed as well as emphysema and hemorrhages as primary lesions in different organs. The experimental data reinforces the pathological findings found in cetaceans with DCS as well as the hypothesis that individuality plays an essential role in DCS, as it has previously been proposed in animal models and human diving medicine