Marine Fishes Pelagic organisms that can actively swim (against a current) are known as nekton Nekton include some invertebrates such as cephalopods and pelagic arthropods such as shrimp and swimming crabs, but most nekton are vertebrates

Phylum Chordata, Subphylum Vertebrata Vertebrates (subphylum Vertebrata) share four fundamental characteristics of the phylum Chordata with 2 invertebrate subphyla – Subphylum Urochordata – Subphylum Cephalochordata Vertebrates differ, however, in the presence of a backbone, or spine, and the presence of an endoskeleton

Subphylum Vertebrata The vertebral backbone consists of a dorsal row of hollow skeletal elements, the vertebrae The vertebrae surround and protect the nerve cord, or spinal cord, which ends in a brain protected by a skull made of cartilage or bone Vertebrates exhibit bilateral symmetry and have a distinct head, and organ systems

Subphylum Vertebrata

Marine Fishes Fishes were the first vertebrates, appearing more than 500 million years ago Jawless fishes Cartilaginous fishes Bony fishes

Marine Fishes Fishes are the oldest and structurally-simplest of all living invertebrates ~Half of all vertebrates are fish! Most species of fish are marine Three groups are fish are currently recognized – Jawless Fishes (superclass Agnatha) – Cartilaginous Fishes (class Chondrichthyes) – Bony Fishes (superclass Osteichthyes)

General Fish Morphology

Jawless Fishes (Agnatha) The most primitive of all living fish are the jawless fish (Agnatha) As they lack jaws, jawless fish must feed by suction with the aid of a round, muscular mouth and rows of teeth Body is cylindrical and elongated like that of an eel or snake; no paired fins or scales – lack true vertebral column! – Cartilaginous skeleton

Jawless Fish (Agnatha) Jawless fish include the hagfish and the lampreys – Hagfish feed mostly on dead or dying fishes; usually found on deep, muddy bottoms Exclusively marine – Lampreys attach themselves to other living fishes and suck their blood and tissue matter Primarily freshwater

Hagfish (left) vs. Lamprey (right)

Cartilaginous Fishes Cartilaginous fishes (Chondrichthyes) have a skeleton made not of bone, but of cartilage, which is lighter and more flexible than bone Cartilaginous fishes have well-developed jaws and paired fins for efficient swimming Most cartilaginous fish also have rough, sandpaper-like skin, the result of placoid scales pointed tip directed backwards

Cartilaginous Fishes Cartilaginous fishes include sharks, skates, rays and chimeras, or ratfishes Nearly all are marine ~350 species of sharks; ~500 species of skates and rays; 30 species of chimeras

Sharks (cue scary, cello music) Sharks are often referred to as living fossils because many of the species alive today are similar to ones that swam the seas >100 million years ago Sharks have powerful jaws with rows of numerous sharp, often triangular teeth – Lost or broken teeth are quickly replaced by another, which shifts forward from the row behind it as if on a conveyor belt

Sharks Sharks have fusiform, spindle-shaped bodies, which cut easily through the water A well-developed, muscular caudal fin propels them through the water; paired pectoral fins enable steering and dorsal fins provide stability

Sharks are efficient predators Many sharks exhibit counter-shading, appearing dark on top and light on the bottom – Camouflage from above and below Why? flmnh.ufl.edu

Sharks, dog bites, lightning strikes, and falling coconuts, oh my! Sharks have five to seven gill slits which are located behind the head for respiration (we’ll come back to this…) More than 80% of all sharks are under 2 meters in length (less than 6.6 feet), and only a few of the remaining 20% are aggressive towards humans FACT: You are more likely to die from a dog bite (or lightening strike) than a shark bite…

Fish are friends, not food… In fact, sharks have WAY more to fear from humans than we do of sharks Shark populations are in considerable decline worldwide – 80% global decline in shark populations! – million sharks killed every year for their fins! – Potential increases in diseased, unfit, and unhealthy prey individuals all-creatures.org

Dramatic decline in shark populations Myers, et al. 2007

Is your dinner endangered?

Rays and Skates Rays and skates have dorsoventrally flattened bodies, with 5 pairs of gill slits on the underside (ventral side) of their body Most are demersal, spending much of their lives on the sea floor Pectoral fins are greatly extended resembling wings

Is it a ray, or a skate? Skates usually have 2 dorsal fins; Rays lack dorsal fins altogether Skates have a muscular tail; Rays have a whip- like tail, usually with a prominent stinger Ray Skate

Chimeras, or ratfishes Approximately 30 species of deep-water, strange-looking cartilaginous fish are grouped separately as chimeras, or “ratfishes” Only one pair of gill slits, covered by a flap of skin Demersal (bottom-dwelling) Some with a long, rat-like tail

To summarize….

Bony Fishes (Osteichthyes) Bony fish (Osteichthyes) are the most successful and abundant of the 2 groups of fishes (96% of all fish; ~27,000 species) Osteichthyes possess a hard, strong - but lightweight - skeleton made of calcium that supports them and is responsible for their success (and diversity) as a group Bony fish include tuna, cod, flounder, goldfish, and other familiar species

Bony Fishes (Osteichthyes) The composition of their skeleton is not the only distinguishing feature of bony fishes In contrast to the tiny, pointed placoid scales of cartilaginous fishes, bony fish usually have cycloid or ctenoid scales, which are thin, flexible, and overlapping – Cycloid scales have a smooth outer edge – Ctenoid scales have a toothed outer edge

Bony Fishes (Osteichthyes) The scales are made of bone and are covered by a thin layer of skin and a protective mucus Bony fish are also characterized by the presence of a gill flap, or operculum

Bony fish have a bony opeculum Cartilaginous fish have gill slits kmle.co.kr

Bony Fishes (Osteichthyes) Bony fish are subdivided into two major groups – Lobe-finned fishes – Ray-finned fishes Lobe-finned fishes are largely extinct, but include lungfishes and coelacanths Ray-finned fishes, in contrast, are far more successful, and can be further divided into soft-rayed and spiny-rayed bony fish

Soft-rayed vs. Spiny-rayed Soft rayed fish representatives include: – Cod – Trout – Herring Spiny-rayed fish representatives include: – Bass – Groupers – Reef fish

Fishes of Long Island CunnerTautogPorgyStriped bass

Fishes of Long Island BluefishBlack sea bassWeakfishMonkfish

Flatfish (“doormats”) of Long Island Winter flounderSummer flounder Windowpane KEY: Right-sided Left-sided

Ontogeny recapitulates phylogeny?!!?