About 25% of fish species are piscivorous, meaning they feed primarily or exclusively on other fish. Piscivory is a common feeding strategy among fish, especially in marine environments where fish are abundant and diverse. However, piscivory is not evenly distributed among fish groups, and some factors such as body size, habitat, and evolutionary history influence the likelihood of a fish being piscivorous. In this article, we will explore the characteristics, adaptations, and examples of piscivorous fish, as well as the ecological implications of fish eating fish.
Piscivorous fish are fish that eat other fish as their main source of food. They can be classified into two types: obligate piscivores and facultative piscivores. Obligate piscivores are fish that can only survive on a fish-based diet, while facultative piscivores are fish that can switch between fish and other prey items depending on availability and preference.
Some examples of obligate piscivores are tuna, swordfish, marlin, barracuda, and shark. These fish are typically large, fast, and powerful predators that can chase and capture their prey in open water. They have streamlined bodies, strong jaws, sharp teeth, and keen senses to aid them in hunting. Some obligate piscivores, such as shark, can also detect the electrical signals emitted by their prey using special organs called ampullae of Lorenzini.
Some examples of facultative piscivores are trout, bass, pike, perch, and catfish. These fish are usually smaller, more flexible, and more opportunistic than obligate piscivores. They can feed on a variety of prey items, such as insects, crustaceans, mollusks, worms, and plants, in addition to fish. They have more diverse body shapes, mouth structures, and feeding behaviors to adapt to different habitats and food sources. Some facultative piscivores, such as pike, can ambush their prey by hiding in vegetation or rocks, while others, such as catfish, can scavenge for dead or injured fish using their barbels and taste buds.
Adaptations of Piscivorous Fish
Piscivorous fish have evolved various adaptations to enhance their ability to catch and consume other fish. Some of these adaptations are:
Gape size: The gape size is the maximum width of the mouth opening of a fish. Piscivorous fish tend to have larger gape sizes than non-piscivorous fish, as this allows them to swallow larger prey items whole or in fewer bites. For example, the gape size of a tuna can reach up to 25% of its body length, while the gape size of a carp can only reach up to 10% of its body length.
Pharyngeal jaws: The pharyngeal jaws are a second set of jaws located in the throat of some fish. Piscivorous fish use their pharyngeal jaws to manipulate, crush, or slice their prey after swallowing them. This helps them to digest their prey faster and more efficiently, as well as to prevent choking or regurgitation. For example, the pharyngeal jaws of a moray eel can move forward and backward to grasp and tear their prey, while the pharyngeal jaws of a cichlid can rotate and grind their prey.
Stomach size: The stomach size is the volume of the stomach of a fish. Piscivorous fish tend to have larger stomach sizes than non-piscivorous fish, as this allows them to store more food and energy for longer periods of time. This is especially useful for fish that live in environments where food is scarce or unpredictable, such as the deep sea or the polar regions. For example, the stomach size of a cod can reach up to 30% of its body weight, while the stomach size of a herring can only reach up to 5% of its body weight.
There are many examples of piscivorous fish in the world, but here are some of the most notable ones:
Great white shark: The great white shark is the largest predatory fish in the world, reaching up to 20 feet in length and weighing up to 5,000 pounds. It is an obligate piscivore that feeds mainly on fish, such as tuna, salmon, and herring, but also on marine mammals, such as seals, dolphins, and whales. It has a powerful bite force of up to 4,000 pounds per square inch, and can accelerate up to 35 miles per hour when attacking its prey. It is also one of the few fish that can breach the water surface, sometimes jumping up to 10 feet in the air.
Piranha: The piranha is a small but ferocious fish that lives in freshwater rivers and lakes in South America. It is a facultative piscivore that feeds on fish, as well as insects, worms, crustaceans, and even mammals and birds. It has a reputation for being a voracious and aggressive predator, capable of stripping the flesh off its prey in seconds. It has a razor-sharp teeth that can cut through bone and metal, and a strong jaw that can exert up to 70 pounds of force per square inch.
Lionfish: The lionfish is a colorful and venomous fish that lives in coral reefs and rocky areas in the Indo-Pacific region. It is an obligate piscivore that feeds on fish, such as damselfish, cardinalfish, and wrasse, but also on crustaceans, such as shrimp and crab. It has a unique hunting strategy that involves using its long and spiny fins to corner and stun its prey, before swallowing them whole. It also has a potent venom that can cause severe pain, swelling, and paralysis to its predators and human divers.
Fish eating fish is a natural and essential part of the aquatic food web, as it transfers energy and nutrients from lower to higher trophic levels, and regulates the population and diversity of fish species. However, fish eating fish can also have negative impacts on the ecosystem, especially when it is influenced by human activities, such as overfishing, pollution, and climate change. Some of these impacts are:
Trophic cascade: A trophic cascade is a phenomenon where changes in the abundance of one species affect the abundance and behavior of other species across different trophic levels. For example, when humans overfish the top predators, such as shark and tuna, this reduces the predation pressure on their prey, such as herring and sardine, which in turn increases their population and consumption of their prey, such as plankton and algae, which in turn decreases their population and production of oxygen and carbon sequestration. This can result in a cascade of ecological consequences, such as reduced biodiversity, altered nutrient cycles, and increased greenhouse gas emissions.
Invasive species: An invasive species is a species that is introduced to a new environment where it does not belong, and causes harm to the native species and ecosystem. For example, when humans introduce the lionfish to the Atlantic Ocean, this increases the predation pressure on the native fish, such as grouper and snapper, which in turn decreases their population and diversity, and disrupts the balance of the coral reef ecosystem. This can result in a loss of ecosystem services, such as tourism, recreation, and fisheries.
Evolutionary response: An evolutionary response is a change in the traits of a species over time due to natural selection. For example, when humans pollute the water with chemicals, such as mercury and PCBs, this increases the toxicity of the fish, especially the piscivorous fish, which in turn affects their survival and reproduction. This can result in a selection for fish that are more resistant or tolerant to the toxins, or a reduction in the size or number of the piscivorous fish. This can result in a change in the genetic diversity and adaptation of the fish species.
Fish eating fish is a common and complex phenomenon that involves various factors, such as body size, habitat, and evolutionary history. Piscivorous fish have different characteristics, adaptations, and examples that reflect their feeding strategy and lifestyle. Fish eating fish also has ecological implications that can affect the structure and function of the aquatic ecosystem, both positively and negatively. Therefore, it is important to understand and appreciate the role and impact of fish eating fish in the aquatic world.
