When fish are caught, blood often emanates from their gills. This occurs due to the delicate nature of their gill structures and their physiological responses to capture stress. Understanding this involves examining both anatomical vulnerabilities and biological reactions.
Gill Anatomy and Function
Fish gills are complex organs primarily responsible for respiration, facilitating the exchange of gases between the fish’s blood and the surrounding water. These specialized structures consist of multiple gill arches that support numerous delicate filaments. Each gill filament is covered with finer, leaf-like structures called lamellae.
Within these lamellae lies an extensive network of microscopic blood vessels, specifically capillaries. This intricate vascularization allows for efficient oxygen absorption from the water directly into the bloodstream. However, this dense arrangement of thin-walled blood vessels renders the gills exceptionally fragile and prone to injury. Even slight physical disturbances can rupture these vessels, leading to bleeding.
Physical Trauma During Capture
Catching a fish often involves physical forces that can directly injure its delicate gill structures. As a fish struggles against a fishing line, it frequently thrashes violently, causing its gill plates to flare open and contract. This vigorous movement can lead to gill filaments rubbing against hard surfaces, such as the fishing line, boat, or net. Such friction can cause abrasions, tears, or ruptures of the gill tissue and its associated blood vessels.
Fishing tackle can inflict direct damage. Hooks, particularly treble hooks, can snag or penetrate the gill arch or filaments during the struggle. Even when a hook is not directly in the gills, the fish’s thrashing can cause the hook or lure to strike and damage the sensitive gill area. Improper handling, such as gripping the fish by its gills or allowing it to flop on a hard surface, can also contribute to physical trauma and subsequent bleeding.
Physiological Factors Exacerbating Bleeding
Beyond direct physical injury, a fish’s physiological response to being caught can amplify bleeding. When a fish is hooked, it experiences an acute stress response. This stress triggers the release of hormones, including adrenaline, into the bloodstream. Adrenaline causes a rapid increase in the fish’s heart rate and blood pressure.
This elevated blood pressure means that any damaged capillaries or blood vessels in the gills will bleed more profusely. The increased blood flow through the gills intensifies blood loss from even minor injuries. Therefore, the fish’s biological reaction to capture inadvertently exacerbates gill bleeding.
Variables Influencing Bleeding
Several external factors and handling practices can influence gill bleeding in a caught fish. The duration and intensity of the fight play a role; a prolonged struggle increases physical trauma and physiological stress, leading to more extensive damage and bleeding. The type of tackle used can also impact gill injury. For instance, large, barbed treble hooks may cause more internal damage compared to smaller, single, or barbless hooks, which are easier to remove.
Handling practices after the fish is caught also contribute to bleeding. Keeping the fish in water or handling it with wet hands can reduce external friction and prevent further damage to the delicate gill tissue. Conversely, allowing the fish to thrash on a dry surface or handling it roughly can worsen existing injuries, increasing blood loss from the gills.