BONY FISH (Class Osteichthyes)

BONY FISH (Class Osteichthyes) EXTERNAL ANATOMY The largest group of fish are the bony fishes and includes As the name suggests, bony fish have a bony skeleton with a eels, seahorses and pipefish. The total number of species of protective bony plate called the operculum covering the gill bony fish is thought to be more than 15,000. cavity and a single external gill slit. Masters of disguise Unlike sharks, many bony fish Eyes Operculum Dorsal fin have bright colours and patterns. Bony fish have well developed eyes with The operculum, or gill cover, The dorsal fin acts like a Fish that live on the sea floor almost 360° vision. is a hard bony plate that rudder or keel on a boat, often have flattened bodies, usually camouflaged in mottled, Unlike sharks, bony fish do not have eyelids. protects the gills. Bony fish keeping the fish upright and neutral colours. Some fish species have false eye spots on have a single gill opening on stable. The dorsal fin can their tails to confuse predators as to which either side of the head. be split into two – the front end is which. spiny dorsal fin plays a role in protection, the second is Fish generally have good eyesight, but eye size Lateral line known as the soft dorsal fin. does vary depending on habitat and behaviour. The lateral line is a series of sensory pores, or receptors, which detect vibrations and pressure Nostril changes in the water. Caudal fin Although fish don’t have a nose they do have The caudal fin or tail as it is more commonly nostrils (or nares) that are used to smell odours known helps with steering, like the rudder on (such as chemicals) in the water. a boat. It also regulates the speed of forward movement. The caudal fin of bony fish is called a homocercal tail because both the upper and lower lobes are Fish chatter the same size (or symmetrical), unlike in sharks Fish produce sounds by rubbing together where the upper lobe is generally larger than the two bony parts of the body, such as their lower lobe (referred to as a heterocercal tail). teeth or spines. Many bony fish move by bending their bodies so their tail finds thrust against the water. Mouth Mouth shape and position often indicates what type of feeder the fish is e.g. upwards facing mouth indicates a surface feeder. Continuous tail: Swims The mouth is very important in ‘breathing’ (gas at slow speed but highly exchange), as water is taken into the mouth and manoeuvrable, enabling access into crevices and passed over the gills, where oxygen is extracted caves (e.g. cobbler). Truncate tail: Cruises and carbon dioxide is released. Pectoral fin Scales at intermediate Bony fishes’ teeth are attached to their jaws. speeds, with increased Pectoral fins are used Bony fish have round, manoeuvrability due to individually to turn the fish overlapping scales, although a larger surface area (e.g. Superior – the mouth is in either direction or control Vent some species have lost mangrove jack). Also positioned towards the their scales and have naked able to accelerate quickly up and down movement. The vent, or anus, is when needed. surface and the fish feed skin (e.g. toadfish, sunfish). on what is above them, When used together, they the external opening Lunate tail: Very fast fish, able to maintain high e.g., garfish and snook. act as brakes or allow the fish to the digestive and Scales serve as a protective covering against bacterial speeds for long periods of to swim backwards. Pectoral reproductive systems. time, but a lack of surface Terminal – the mouth is fins are absent in eels. infection and parasites. The area means they can’t positioned in the middle skin also has thousands of stop or turn easily or swim of the head and the fish Fins backwards (e.g. tuna). either chase prey or feed mucous glands embedded on what is ahead of them, The fins of bony fishes Ventral (Pelvic) fin in it. These secrete mucous e.g., tuna and tailor. are membranous and The paired pelvic (or ventral) that in turn provides an Rounded tail: Swims at fins assist with balance and additional protective coating intermediate speeds, with Inferior – the mouth is strengthened by a series greater manoeuvrability positioned towards the of spines or soft rays. steering, including side- to the fish, makes it more and able to accelerate bottom and the fish prey Unlike the rigid fins of to-side and up and down Anal fin streamlined for movement quickly for short periods Forked tail: Cruising fish upon or scavenge/graze sharks, the fins of most movement, as well as The anal fin assists with through the water and (e.g. estuary cod). benthic food sources, e.g., that swim continuously at whiting and cobbler. bony fishes can be folded acting as brakes to slow stability, stopping the fish prevents any water leaking very fast rate (e.g. tailor and flat against the body. the fish down. rolling from side to side. into the fishes’ body. Australian herring). Extra fin surface provides more Sponsored by: manoeuvrability than fish with a lunate tail. Department of Primary Industries and Regional Development Marine Waters marinewaters.fish.wa.gov.au Illustrations © R.Swainston/www.anima.net.au | 2871/17