Aquatic and Marine Biology

Most bony fish possess a swim bladder (also called air bladder) - a gas-filled organ that allows them to regulate buoyancy and maintain depth without expending energy. By adjusting the gas volume, fish can achieve neutral buoyancy. Cartilaginous fish like sharks lack this organ and must swim constantly to avoid sinking.

Cetaceans (whales and dolphins) have the most developed intelligence among aquatic animals. Dolphins, in particular, demonstrate advanced problem-solving, complex social behavior, self-recognition, and sophisticated communication. While sharks are efficient predators, their cognitive abilities are far below those of cetaceans.

Paramecium obtains O₂ from air or water through general body surface.

The stonefish (Synanceia) is widely considered the most venomous fish in the world. Its dorsal spines deliver potent neurotoxins that can cause extreme pain, paralysis, and even death in humans. Sharks are dangerous but not venomous; starfish are generally harmless.

Starfish are echinoderms, a completely different phylum from fish. Sharks, eels, and seahorses are all vertebrates in the fish phylum, while starfish are invertebrates with radial symmetry and a water vascular system.

The saltwater crocodile, also known as the estuarine crocodile, Indo-Pacific crocodile, marine crocodile, sea-going crocodile or informally as saltie, is the largest of all living reptiles.

Benthos is the community of organisms that live on, in or near the seabed, also known as the benthic zone. This community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.

Spongilla is a fresh water sponge.

In starfish, locomotion is done by tube feet.

Chondrichthyes includes cartilaginous fish.

It sinks because it is more dense than water.

Bindin is a species-specific protein found on the acrosomal process of sperm that recognizes and binds to receptors on the egg's vitelline membrane. This mechanism ensures that fertilization occurs only between gametes of the same species.

Pelagic fish live in the water column of the open ocean rather than near the bottom. Herring is a major pelagic species in the North Sea, whereas Cod and Halibut are demersal (bottom-dwelling) fish.

Starfish, or sea stars, belong to the phylum Echinodermata, which is characterized by radial symmetry and a water vascular system. They are marine invertebrates and are not related to fish (which are vertebrates). Amphibians and reptiles are also vertebrates and belong to different classes.

Pisciculture is the controlled breeding and rearing of fish, usually for food. It is a specific branch of aquaculture. The study of birds is ornithology, the culture of honey bees is apiculture, and the study of snakes is ophiology.