Abstract
Based on observations made by fishermen and local residents of Qeshm Island as well as information and news published by news agencies and media, in some parts of the coastal waters and the southern coasts of Qeshm Island as well as the coastal waters in the southeast of Hengam Island, a large number of filefish carcasses have been observed. In an area approximately 55 km long, these carcasses were distributed heterogeneously and scattered in several coastal - marine areas from June 17 to 20 this year. The total amount of dead fish in the approximate estimate was about 200 kg. Unfortunately, in the very first hours after the release of the photos and videos and unsubstantiated and unrealistic suspicions that cause concern in the minds of the public and local residents were quickly spread in cyberspace and in some cases the identified species was declared wrong. Therefore, according to the importance of this issue and the need to conduct the necessary studies and research to investigate the situation and determine the cause or causes of fish mortality and provide the necessary information to the local community and fishermen, an expert team from the Environment Office of the Qeshm Free Area Organization was sent to the site. The expert team thoroughly monitored the coasts for field surveys, sampling, local information collection and documentation. Simultaneously with the actions taken on the island, the issue was investigated based on archival sources as well as related articles and reports inside and outside the country, as well as analysis of information and data collected to investigate various scenarios and possible causes raised by researchers and experts in marine ecosystems at the headquarters of the Iranian Fisheries Science and Research Institute and the Persian Gulf and Oman Sea Ecological Research Institute - Bandar Abbas. In this regard, a complete report has been prepared and will be published by the institute soon. In this report, while documenting and collecting the required information and data based on field, laboratory and questionnaire studies, the background of previous studies and chronicles of similar phenomena were used. Also, thematic analysis has been performed based on multi - directional matrix research and suggestions and management - executive solutions have been presented.
Results
According to ichthyological research and matching the appearance of dead fish specimens, all specimens belong to the family "Monacanthidae" with the scientific name Paramonacanthus choirocephalus, which in English is called "Pig faced filefish" and in Arabic is called "Buqumi". It is possible to identify this fish incorrectly because of the physical similarity of this species with three other similar species of the same family. The main habitat of these fish is in shallow coastal areas and continental shelf areas to a depth of less than 50 meters and often up to 25 meters. This fish is distributed in all seas of tropical regions and the Indian Ocean, as well as the seas in southern Iran (Persian Gulf, Strait of Hormuz and Gulf of Oman). They depend on enclosed habitats and sandy beds around rocky areas and coral reefs. They are also found in waters around artificial habitats and sunken ships and equipment. Behaviorally, these fish have slow swimming movements, do not migrate, and live mostly alone. They feed on a variety of phytoplankton and zooplankton, benthic invertebrates and sponges. In some cases, algae and seaweed are also included in their diet. This species and other similar species of the filefish family are not commercially valuable for fisheries and food, and as a result they are not considered as target species for fishermen. But in terms of color and appearance, it is in the group of ornamental fish that are kept in saltwater aquariums. They are mainly considered as by – catch fish and discarded by the bottom trawlers. In terms of national and global conservation classification, although no detailed assessment has been made so far, due to its lack of economic and fishery importance for human consumption, there is no concern about the resources and population of this species. Therefore, in the current situation, there is no need to implement conservation programs.
- Examination of the time period of fish carcasses revealed that in terms of the area covered, scattered areas of about five areas on the south coast of Qeshm Island with a length of about 55 km, including the coastal waters in the southeast of Hengam Island, the coasts of Salakh Village, Mesen Village, Suza Village, Naz Islands, and the southeastern shores of Qeshm Island, different densities of fish carcasses were brought to shore, which did not have a specific pattern and were in fact heterogeneous and scattered in several coastal - marine areas. Density per unit area was estimated at an average of about 10 fish per square meter, which is a significant volume in terms of fish mortality. Also, morphometric measurements and weighing of fish samples showed that in terms of size, fish length ranged from 9 to 16 cm with the average length of 13 cm and fish weight ranged from 22 to 43 g with the average weight of 35 g. Therefore, it seems that the samples of dead fish, based on the average length and weight announced for adult specimens of this species in scientific resources, often had the maximum age and in the adult stage. The total amount of dead fish in the approximate estimate was about 200 kg. Considering the average weight obtained (35 g) for a sample, it seems that about 5500 – 6000 fish have died. On the other hand, due to the fact that the behavioral characteristics of this species are such that it does not migrate and forms the shoal, and on the other hand, the formation of school for feeding and reproduction has not been reported in the scientific reports and resources. Therefore, in this regard, it is a unique case in terms of the number of fish in the constituent herd.
- Examination of the dead fish samples showed that they had no physical injuries, parasites or skin damage (due to bacterial and fungal diseases) and they were generally healthy. Clinical observations also showed that there were no symptoms of disease in tissues covering the external surfaces of the body. However, due to partial autolysis, it was not possible to examine the internal organs. The results of the study of the presence of pathogenic and opportunistic pathogenic bacteria in the intestinal samples showed high diversity and abundance of bacteria. Identification of isolated bacteria using morphological, biochemical and physiological identification methods confirmed the presence of a wide range of pathogenic species including Vibrio parahaemolyticus, Pseudomonas aeroginosa, Aeromonas sp., Streptococcus sp. The mentioned bacteria were not present in the eye samples, but two species of V. parahaemolyticus and Aeromonas sp. were identified in the gill samples.
Conclusion
At first glance, to investigate the cause of fish mortality, the fisheries by - catch hypothesis is proposed. In this regard, it can be said that if the fishing factor is involved, the process of fish mortality has been such that a population of this species has been considered as by – catch fish (non – edible fish) and discarded by the bottom trawlers (albeit with reference to illegal and unlicensed fishing) including industrial trawlers or possibly traditional trawlers (Gufa). The ecological characteristics of the species (habitat, nutrition), parallel longshore currents and geological conditions of the area (coastal landforms) in the southern parts of the island have caused carcasses to accumulate on the beach in some parts. Based on field visits and the study of the subtidal area up to the depth of 10 meters by a group of divers (June 17), a significant number of half - dead fish have been observed swimming very slowly near the seabed. Therefore, it seems that a group of fish that were caught in the fishing nets for hours and released back into the sea, moved near the shore at a depth of less than 10 meters and their carcasses came to shore after death with coastal currents and tides. However, due to the fact that this fish is not in the fishing basket of traditional (and even industrial), ornamental and even commercial fishermen, and no activities have been reported for the exploitation of this type of fish in the south of the country (Hormozgan and Qeshm area), the above hypothesis is probably not valid. Due to the fact that this species does not have a known and permanent herd behavior and lives mainly individually in rocky beds and around coral reef habitats, hence the uniform accumulation of single carcasses and the scattering of carcasses in the coastal area with a length of about 55 km also rejects the fisheries by - catch hypothesis. Because there is basically species diversity in the dead by – catch fish population and it includes a combination of different types of fish that such a thing has not been observed.
- Another hypothesis discussed is the effect of toxic plankton bloom (Hazard Algae Bloom - HAB) due to the density and production of a group of toxic plankton (e.g. the group of dinoflagellates) and active feeding of these fish has caused their poisoning and eventually their death. However, according to regional monitoring and continuous satellite and field surveys, there have been no reports of pollution and red tides during the days of fish mortality. In addition, contaminants and red tides are generally not selective in causing mortality in aquatic populations and affect a range of different species of animals. Therefore, the possibility of the effect of the red tide phenomenon on fish mortality cannot be confirmed. Despite autopsy studies for microbiological tests (pathology), the contents of the gastrointestinal tract (intestines and stomach) of fish carcasses could not be identified and since feeding is generally a selective behavior for these fish, the nutritional factor may be involved in the death of these fish.
- Regarding the hypothesis of the presence of pathogens, according to the obtained results, the presence of four species of pathogenic and opportunistic pathogenic bacteria in the samples of dead fish was confirmed. However, no external clinical signs were observed in the samples. Pathogenic bacteria can live in the body of an aquatic organism for a long time and cause death in cases of stress to the aquatic organism (such as oxygen depletion). Among these, the role of species belonging to the genus Streptococcus in the development of the disease seems to be significant. Due to the high abundance of this bacteria and its predominant presence in the intestinal samples of the studied fish, the possibility of streptococcal infection is higher than other infections. Hence, the development of streptococcal infection can be considered as a strong possibility for the resulting mortality. However, these results do not rule out the possibility of other viral and parasitic pathogens.
- The hypothesis of chemical pollution such as industrial effluents and oil pollution is very weak and cannot be confirmed due to field studies, the lack of reports on chemical pollution and observations indicating a single species mortality pattern. It is also possible that due to the synchronization of the mortality phenomenon with the highest tide (due to the lunar eclipse phenomenon and the peak of tide changes), the level of dissolved oxygen in the water has dropped to an unbearable level for this species and has caused the mass death of this fish, which is called summer disease. Obviously, based on the scientific resources and the available evidence, other scenarios such as heat shock due to severe temperature fluctuations and even natural mortality, due to lack of evidence, cannot be acceptable reasons for mass mortality of filefish.