Deep-water marine fish living on the continental slopes at depths from 2,000 feet to one mile have liver pathologies, tumors and other health problems that may be linked to human-caused pollution, one of the first studies of its kind has found.
The study was conducted in the Bay of Biscay by scientists from Oregon State University and the Centre for Environment, Fisheries and Aquaculture Science in the United Kingdom, with sampling taking place in an area with no apparent point-source pollution, thus appearing to reflect general ocean conditions. The researchers also discovered the first case of a deep water fish species with an “intersex” condition, a blend of male and female sex organs.
Fish were obtained from the north east region of the Bay of Biscay (north east Atlantic Ocean) by trawling at depths between 700 and 1400 m. Liver and gonad samples were collected on board ship and fixed for histological processing and subsequent examination by light microscopy. The physiological ailments identified were found in black scabbardfish (Aphanopus carbo), orange roughy (Hoplostethus atlanticus), greater forkbeard (Phycis blennoides) and other less-well-known species, and included a wide range of degenerative and inflammatory lesions that indicate a host response to pathogens, as well as natural cell turnover (a pathogen is a biological agent that causes disease or illness to its host). Hepatocellular and nuclear pleomorphism and individual cases of ovotestis and foci of cellular alteration (FCA) were detected in black scabbardfish. Six cases of FCA were observed in orange roughy (Hoplostethus atlanticus) together with a single case of hepatocellular adenoma.
“In areas ranging from pristine, high mountain lakes of the United States to ocean waters off the coasts of France and Spain, we’ve now found evidence of possible human-caused pollution that’s bad enough to have pathological impacts on fish,” said Michael Kent, a professor of microbiology in the OSU College of Science, co-author the study and an international expert on fish disease.
“Deep in the ocean one might have thought that the level of contamination and its biological impact would be less,” Kent said. “That may not be the case. The pathological changes we’re seeing are clearly the type associated with exposure to toxins and carcinogens.”
As the sea deepens along the continental slopes where these species live, it’s been known that it can act as a sink for heavy metal contaminants such as mercury, cadmium and lead, and organic contaminants such as PCBs and pesticides. Some of the intersex fish that have been discovered elsewhere are believed to have mutated sex organs caused by “endocrine disrupting chemicals” that can mimic the hormone oestrogen. Very few, if any, health surveys of this type have been done on the fish living on the continental slopes although the physiological effects of anthropogenic pollution on marine organisms elsewhere have been studied extensively.
The endocrine system of organisms refers to the collection of glands that secrete hormones directly into the circulatory system, to be carried towards target organs containing cells possessing the appropriate receptor. The major endocrine glands include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus, gastrointestinal tract and adrenal glands. Endocrine disruptors are chemicals that at certain doses, can interfere with the endocrine (or hormone system) in animals. Endocrine distrupting agents were defined by USEPA (1997) as “an exogenous agent that interferes with the synthesis, secretion, transport, binding, action or elimination of natural hormones in the body that is responsible for the maintenance of homeostasis, reproduction, development and/or behaviour”. These disruptions can cause cancerous tumors, birth defects, and other developmental disorders. Types of hormones secreted via the endocrine system include Steroids, Peptides and Amines. Produced mainly in the gonads (i.e testes (testorsterone) and ovaries(Estradiol)), steroids are lipids and are believed to be the most susceptible hormone to toxic action from anthropogenic chemicals.
Due to the small size of steroid hormones, they can diffuse through the cell membrane where they bind to a steroid receptor inside the cytoplasm, from where the steroid-receptor complex is translocated to inside the nucleus. Here the complex binds to a receptor site located on the DNA strand. The initiation of transcription occurs (synthesis of RNA molecules) and the RNA is transported to the cytoplasm where protein synthesis occurs. In the marine environment, there are many anthropogenic pollutants present that can bind to the steroid receptors in the cytoplasm or cell membrane (hormone mimicry) where the response induced is identical to that caused by hormones.
These hormone mimicking chemicals can block the hormone receptor, interfering with the signal from the body hormones so no response is initiated. However, in some cases a hormone mimicking substance can produce a signal stronger than the body’s hormones, as well as a weaker signal, both of which can result in detrimental effects to the exposed organism. Known endocrine disrupting chemicals include phytoestrogens, plant-derived xenoestrogens not generated within the endocrine system but consumed by eating phytoestrogenic plants, as well as Polychlorinated Biphenyls (PCBS) contained in hydraulic fuels and flame retardants.
Antifouling agents containing substances such as TBT (Tributyltin) have been used since the 1960s on ship’s hulls and fish farm nets to prevent the fouling of surfaces by marine algae and sessile organisms through the slow release of the toxic TBT from paint. The first endocrine-mediated effects of TBT were observed in oyster populations at the Bay of Archachon. Shell deformities were observed in the oysters as well as the inability of the juvenile oysters to settle and attach to the substrate. These effects of TBT led to the breakdown of local oyster production in the area with economic consequences. Intersex in species of freshwater fish has also been observed in the River Lea during the 1980’s as a result of endocrine disruptors. Sections of gonads of the Roach fish showed to contain developing eggs. Subsequent research showed sewage effluent that was oestrogenic to the fish (due to estrogen present in birth control pills and hormone therapy drugs) could influence the reproductive development and success of the fish as well as yolk protein precurssors (vitellogenin) in the male fish.
Endocrine disruptors in the environment have also shown to have detrimental effects to some human physiological processes. The decline in sperm count in humans as well as an increase in rates of testicular cancer diagnosis are believed to be a result of exposure to various pesticides that humans have been in contact with over the last century.
Ultimatley, the physiological effects of pollutants on marine organisms are varied and are dependant on the site of absorption and the molecular properties of the contaminant itself. Physiological processes known to be impacted by exposure to contaminants include the respiratory system, cardiovascular system, oxidative metabolism, osmoregulation, feeding and nutrition, reproduction, neurological effects and behaviour. The type of exposure will have a significant affect on the organisms physiology also, with acute exposures such as oil spills and ship wrecks releasing waste leaving no time for physiological adaptation by the organism. This can lead to immediate mortality in organisms or significant illness and disease throughout a population. Chronic exposures (lower level and gradual) as described in this study, have often shown that physiological systems in organisms can adapt to the contamination, through acclimation (tissue repair) allowing the organism to maintain performance under new environmental conditions.
In a previous study by OSU conducted in the American West, scientists found toxic contamination from pesticides, the burning of fossil fuels, agriculture, industrial operations and other sources, which primarily found their way into high mountain lakes through air pollution. Pesticide pollution, in particular, was pervasive. Together, the two studies suggest that fish from some of the most remote parts of the planet, from high mountains to deep ocean, may be impacted by toxicants, Kent said.
The study has been published in Marine Environmental Research.
S.W. Feist , G.D. Stentiford, M.L. Kent, A. Ribeiro Santos, P. Lorance.Histopathological assessment of liver and gonad pathology in continental slope fish from the northeast Atlantic Ocean. Marine Environmental Research, 2015
Header Photo Credit:
A ship floats amongst a sea of spilled oil in the Gulf of Mexico after the BP Deepwater Horizon oilspill disaster, an example of large scale oceanic pollution – kris krüg