Marine Fishes

BIOL265Dave Werner

Kingdom Animalia – Phylum Chordata

Major Characteristics found in all chordates:

1. Notochord – a stiff but flexible rod along the length of the body

2. Dorsal hollow nerve chord – neural structure that develops into the brain and and central nervous system

3. Pharyngeal gill slits – openings or grooves found on the cavity behind the mouth(found in all chordates at least at some stage of their life cycle)

4. Post-anal tail

Kingdom Animalia – Phylum ChordataSubphylum Urochordata : Tunicates - ~1400 entirely marine species, including

sea squirts.

Sessile, filter feeders…

Body may look like that of a spongebut they have a leathery outer protectivelayer called the tunic that feels very different from sponges… internally, theyare quite complex…

Kingdom Animalia – Phylum Chordatasubphylum urochordata

Although urochordates are sessile, they typically have motile larvae that truly exhibitall the chordate characteristics…

In a few cases however (i.e. salps); the urochordates retain the larval form evenas adults, remaining motile…

Tunicates

Also, tunicates may be solitary… … or colonial

What would be the advantages or disadvantages of each of these lifestyles?

Kingdom Animalia – Phylum Chordata

Subphylum Cephalochordata : Lancelets - ~ 29 species of small “fish-like” organisms with all the typical “fish” characteristics, other than a backbone… They live on soft bottoms, and use gill slits to filter feed…

Kingdom Animalia – Phylum Chordata

Subphylum Vertebrata :

The vertebrates represent a diverse group of animals…

Simply put however, they are chordates with a backbone.

Their backbone (or vertebralcolumn, or spine) is made up ofa dorsal row of hollow skeletal elements that protect the nervecord (or spinal cord).

Marine Fishes

Class Agnatha – Jawless fishes … feed by suction and help from their round muscularmouth with rows of teeth…

Include hagfish (or slime eels) that feed on dead or dying organisms… sometimes from the inside out!!! … include about 20 species.

Other agnathans include lampreys which either feed on invertebrates, orattach to other fish and such their blood… include about 30 species.

Jawless FishPhylum: Chordata

Sub-Phylum: Vertebrata

Class: Agnatha

• There are two primary marine types of the class Agnatha. They are Hagfish and Lampreys.

• Most Primitive living fishes• Hagfish are of the order, Myxiniform. They are

related to the slimefish. They have the peculiar habit of tying themselves into knots in order to shed their slime coat and make a new one.

Hagfishes

• 20 known species• Deep, cold waters• 2.6 ft.• Skin is used for leather goods

Hagfish• feed on polychaete worms, shrimp, and dead or dying fish • attach to fish, form a knot in the tail and pass it forward to rip off flesh. Image

© BIODIDAC. • usually enter coelomic cavity and feed on soft parts

• many mucous glands present for antipredator defense

Lampreyshttp://itech.pjc.edu/jwooters/zoology/virtual_review/lamprey.htm

• Lampreys are of the order, Petromyzontiform. They are suckers and attach themselves to fish in order to parasitize off them.

• Found in Freshwater• 30 species

Sea Lamprey Life Cycle• A. Sea lampreys go through an extended larval phase before metamorphosing into the bloodsucking

parasitic phase. Each summer and fall there is one group of parasitic sea lampreys actively feeding in the Great Lakes.

B. The next spring, that group leaves the lake and migrates into tributary streams where they must build nests in clean gravel with flowing water.

C. Each female spawns an average of 60 to 70 thousand eggs.

D. After hatch, the larvae drift downstream to areas with slower currents and sand/silt bottoms. There, they establish permanent burrows and enter a larval stage varying in duration from 3 to 10-ormore years.

E. Larvae lack eyes and the oral disc. Living concealed in their burrows, they are harmless and filter microscopic material from the water for food. When they reach lengths of 120 mm or more, some individuals begin metamorphosis in mid summer.

F. During metamorphosis they develop eyes, the oral disc, and changes in their kidneys that (in their native range) would allow them to enter the salt water of the Atlantic Ocean. That fall or the following spring, they instead enter the Great Lakes to feed parasitically on fish that summer and fall, and mature and spawn the next spring—completing their life cycle. Sea lampreys only spawn once and then die after spawning.