Fish Biology

1. Fish Biology Oceans 11 – May 2012

2. Fish Distribution • Most of the world’s fishes are continental – they live either as part of the freshwater systems on land or as sea-dwellers staying near the coastal environment. • Why? • Rich source of nutrients due to discharge by rivers, upwelling from the ocean, aeration due to surf/tide/waves and penetration of sunlight. • Upwelling = winds push surface water offshore, which is then replaced by nutrient-rich deep waters.

3. Fish Anatomy • Exterior Anatomy: • Agnatha – backbone is called a notochord, which is a rod-like structure made up of special notochordal tissue. • Chondrichthyes – backbone is a notochord surrounded by rings of cartilage, known as the vertebrae. Sometimes this cartilage calcifies and becomes hardened like bone. • Osteichthyes – have bony vertebrae that are united to form the backbone; the notochord is no longer present

4. Appendages • Fish have fins as their appendages • Fins can be median (alone) or paired (in pairs). • Median fins are located along the centerline of the body (top, bottom and end) • Top fin = dorsal = acts as a “keel” to keep fish stable during quick turns • Fleshy fin = adipose fin = stability • Bottom fin = anal fin = stability; can be used to slow down • End fin = tail or caudal fin = propulsion

5. External Anatomy Cont’d • Paired fins : • pectoral fins = “arms/legs” of a fish • Pelvic/ventral fin = maneuverability

6. External Anatomy: Scales • Scales are colorless. Fish usually get their color from various structures underneath the scales. • Scales can be arranged two ways: • Imbricate = overlapping like shingles on a roof • Mosaic = fitting closely together • Four types of scales: • Placoid • Cosmoid • Ganoid • Leptoid – found on bony fishes – like our perch!

7. Internal Anatomy – Circulation, Respiration, Temperature • Blood transports oxygen, nutrients and waste • Single circuit circulation – heart-gills-body-heart • Two-chambered heart with upper atrium and lower ventricle (in contrast to our 4-chambered heart) • Fish get oxygen from water via their gills, which requires a huge amount of energy • Therefore gills must be efficient. They are made efficient in the following ways: large surface area, short diffusion, water flows one way over the gills, use of countercurrent circulation

8. Continued… • Fish are cold-blooded – their body temperature varies with the surrounding environment • Some fish have evolved to be warm-bodied (tuna) • By “locking in” their body heat, they are able to contract their muscles 3 times as fast as a cold-bodied fish, giving them more power and more speed.

9. The Swim (or gas) Bladder • Reduces the density of a fish so that it can float • Sea water is the most dense type of water, therefore salt water fish need smaller swim bladders than fresh water fish • Fish get gas for their swim bladder in a few ways: • Swallowing air when surfacing • Transferring gas from the blood stream to the swim bladder when at great depths.

10. The Lateral Line Sensitive to differences in water pressure nearby Neuromast = bundle of sensory cells = what makes the lateral line sensitive

11. Fish Reproduction • Most fish lay eggs • Three methods of reproduction: • Heterosexual – male/female mating • Hermaphroditic – a single fish is both male and female, producing both egg and sperm. Some of these fish undergo fertilization with similar hermaphroditic fish, and others self-fertilize • Parthenogenetic – unfertilized eggs develop into embryos