Food Preferences and Resources

As a group, bony fishes have a diverse range of food preferences. Some are herbivores (plant-eaters); some are carnivores (meat-eaters); some are omnivores (plant- and meat-eaters); and some are detritivores (animals that eat decomposing plants and animals).

As a group, bony fishes can eat all sizes of plants and animals, from microscopic plant plankton to some of the largest marine animals.

Some of the animals common in the diets of bony fishes include: annelid worms, marine snails, mussels, clams, squids, crustaceans, insects, birds, amphibians, small mammals, and other fishes.

Food Intake

The amount of food a bony fish eats is directly related to its size, its metabolic rate, and the temperature of its environment.

• Smaller fishes generally have a higher metabolic rate than large fishes of the same species. Thus, small fishes generally eat proportionately more.
• Warm-water fishes generally require more food than similar-size cold-water fishes. A fish's body temperature - and its metabolic rate - is determined by the temperature of its environment.

Some bony fishes can go long periods without eating. Some freshwater eels (Anguilla spp.) can survive more than a year without food.

Some researchers have calculated food intake for some species.

• In one study, bluegill (Lepomis macrochirus) - a species of small freshwater fish - ate between 1% and 35% of their body weight in food per week, depending on water temperature.
• Studies on anchovies (family Engraulidae) during the summer showed a food intake of about 8% to 10% of body weight per day.

Methods of Collecting and Eating Food

Many bony fishes, such as mackerels and tunas (family Scombridae), seabasses (family Serranidae), and others are active predators. Like other predators, they often select weak, ill, injured, or dying prey because it is easier to catch.

Some bony fishes, such as anchovies (family Engraulidae) are filter feeders. They strain plankton from the water with gill rakers.

Many bony fishes, including catfishes (Family Ictaluridae) are adapted for bottom feeding.

A species' particular mouth shape and teeth are adapted to accommodate a particular diet.

• The wolf eel's (family Anarrhichadidae) large canine teeth grasp its shelled prey. Its blunt molars crush the shells.
• The blue sucker's (Cycleptus elongatus) thick, nubby lips help it suck plants from rocks.
• A parrotfish's (family Scaridae) chisel-like teeth, in a beaklike mouth, nibble on reef-building corals. These fish are herbivores that eat the algae within the coral. In the process, they grind the coral's hard exoskeleton and defecate sand.

Some bony fishes are quite specialized for feeding. Here are just a few examples:

• A billfish (family Istiophoridae) uses its long bill to stun prey.
• An archerfish (Toxotes jaculatrix) shoots water "bullets" at insects as high as 1.8 m (5.9 ft.) above the water, knocking them to the water's surface.
• Lying at the bottom of the ocean and looking more like a rock than a fish, a stonefish (Synanceja spp.) waits for prey to come to it. When an unsuspecting animal swims by, the stonefish swiftly gulps it.
• The 91 cm (3 ft.) arawana (Osteoglossum bicirrhosum), a freshwater fish of South America, can leap entirely out of the water to seize small birds.
• Some fishes produce strong electric current to stun prey. The electric catfish (Malapterurus electricus) can produce 350 volts of electricity. The South American electric eel (Electrophorus electricus) can produce up to 650 volts of electricity.
• Some species of bony fishes, notably the cleaner wrasse (Labroides dimidiatus), are "cleaners" that pick debris and parasites from larger fishes.