Cancer, characterized by the uncontrolled growth of cells, is a biological phenomenon observed across many species. Fish, like other animals, can develop various forms of cancer. This highlights the deep conservation of cellular mechanisms for abnormal cell proliferation.
Fish and Tumors
Tumors in fish can manifest in diverse ways, often appearing as visible bumps or lumps on the body, head, or fins. Internal tumors, however, are not always apparent externally and can lead to symptoms such as swollen abdomens or changes in swimming and eating behaviors.
While not all abnormal growths in fish are cancerous, many are malignant. Various types of tumors have been identified, including fibromas and sarcomas. Pigmented tumors like melanomas can also occur, particularly in species such as Gypsy-swordtail fish. Gonadal tumors, affecting reproductive organs, are reported in species like koi and northern pike.
Factors Contributing to Cancer in Fish
Environmental contaminants play a significant role in the development of cancer in fish. Polycyclic Aromatic Hydrocarbons (PAHs), industrial byproducts, can accumulate in aquatic sediments and lead to liver and skin cancers in bottom-dwelling fish. Heavy metals such as arsenic, lead, mercury, cadmium, and chromium, discharged into waterways, can also be absorbed by fish and contribute to tumor formation.
Pathogens, particularly certain viruses, are another factor linked to cancer in fish. Retroviruses, herpesviruses, and iridoviruses have been associated with various neoplastic diseases, including skin tumors and fibromas in different fish species. These viral infections can trigger abnormal cell growth.
Genetic predispositions also influence a fish’s susceptibility to cancer. Some species or specific genetic crosses, such as the platy-swordtail cross, are known to have a higher likelihood of developing certain cancers like malignant melanoma. Zebrafish, for example, are frequently used in cancer research due to their conserved cancer genes and their ability to develop tumors that resemble human cancers.
Ecological Implications
The prevalence of cancer in fish populations serves as an indicator of environmental health. Fish are considered bioindicators because their constant exposure to their aquatic environment means their health reflects habitat quality. High rates of tumors in fish can signal significant chemical contamination in a particular body of water.
Widespread cancer can impact fish populations by reducing reproductive success and increasing mortality rates. Fish affected by large or internal tumors may experience difficulty swimming or feeding. This can disrupt the natural balance of aquatic ecosystems, as fish play an important role in nutrient cycling and food webs. Monitoring cancer rates in fish helps scientists understand the long-term effects of pollution on aquatic life and the broader ecosystem.
What This Means for Human Health
There is no scientific evidence indicating that humans can contract cancer from eating fish that have tumors. Consuming cooked fish generally denatures any potential pathogens or substances that might be present in the fish. The primary concern for human health related to fish consumption from polluted waters primarily involves the accumulation of toxic chemicals, such as heavy metals or persistent organic pollutants, within the fish tissue.
Research into cancer in fish contributes to a broader understanding of cancer biology. Since fish and humans share many fundamental genetic pathways involved in cancer development, studies on fish models can provide insights into human cancers and potential treatment strategies.