If you practise scuba diving, you may encounter the most diverse animal species, thanks to the incredible biodiversity of the deep sea.
Many believe diving is an extreme sport, but the truth is it offers wonderful sensations where nature envelops you as you discover unique landscapes. Below we'll discuss marine curiosities...
Types of feeding
Fish feeding habits are highly diverse. Based on their dietary patterns, we can classify them into three main groups:
- Herbivores: these are relatively few, found in both fresh and saltwater. They feed on algae and marine plants.
- Carnivores: these feed on worms, crabs, other fish, or insects and molluscs. Examples include sharks and tuna, among others.
- Omnivores: those that feed on both animals and plants.
The diet of larvae or juveniles is typically very different from that of adults. Most larvae feed on zooplankton, mainly rotifers, copepods and cladocerans.
Feeding strategies
Based on how they obtain food, we can also categorise fish as filter feeders, predators and detritivores.
- Predators actively chase their prey to capture it. These carnivorous animals share common characteristics; they're fast species with hydrodynamic bodies, well-developed vision and smell, and undoubtedly good dentition. Tuna, bonito, barracuda and many sharks are excellent examples of large predators that devour vast quantities of sardines and similar fish.
- Detritivores feed on organic matter deposited on the seafloor. The term detritivore thus refers to omnivores that feed on decomposing plant and animal particles. Many detritivores exist among species inhabiting ocean floors where food is scarce.
- Filter feeders consume plankton which they separate from water and concentrate using specific filtration methods. Typical filter feeders include sardines and anchovies. They possess gill rakers, gill-derived structures resembling spines that form a filter to trap plankton. Even the largest fish on our planet, the whale shark (Rhincodon typus), is a filter feeder. Unlike most sharks, it doesn't have true teeth - they're reduced and the gill arches are equipped with fine plates that act as filters.
Hunting strategies
Some predators prefer to hunt alone like pike (Esox lucius) - freshwater fish - while others hunt in groups, like tuna (Thunnus thynnus), which gather to pursue schools of fish.
Others prefer to remain unnoticed and ambush their prey. Scorpionfish and sea robins camouflage perfectly among rocks, where they wait motionless for prey to approach before striking unexpectedly.
Some possess the ability to generate electric shocks, like the electric ray (Torpedo torpedo) or electric eels (Electrophorus electricus) among others, used either for defence or to stun prey.
To attract victims, some fish use lures, like the anglerfish (Lophius piscatorius), which has a highly modified first dorsal fin that when wiggled resembles a worm. The stargazer (Uranoscopus scaber) is a sedentary fish that lives buried in the seabed, exposing only its eyes and an oral tentacle used to attract prey.
Abyssal species often possess special organs called photophores that can emit light. These photophores are often strategically placed near the mouth or sensory barbels to attract other fish.
Interesting feeding methods
Many species form associations with others for mutual benefit. Remoras, for example, have a dorsal sucker on their head allowing them to attach to sharks or other large fish, enabling them to feed on shark leftovers for free. Remoras may also feed on sharks' external parasites, creating mutual benefits.
Cleaner fish (Labroides dimidiatus), small fish from the wrasse family, feed on other fish's external parasites. They can even enter the mouths of much larger fish without being eaten. A fish needing cleaning services spreads its fins or opens its mouth to show the area needing attention. However, the false cleanerfish (Aspidontus taeniatus) mimics the colours and movements of the real cleaner, biting the fins of fish expecting cleaning services instead.
Locating food
Fish have developed various mechanisms to detect food or attract prey, some quite remarkable.
Fish possess a sixth sense, the lateral line - special scales with nerve endings that detect water vibrations. This allows them to detect potential predators or prey at a distance. This organ proves particularly useful in low-visibility environments.
Some fish like the red mullet (Mullus surmuletus) have sensory barbels near the mouth used to scour the seabed for food. Smell and hearing also play important roles in prey detection.
