Fish Anatomy For Fish Breeding

Don M. Velasquez

INTERNAL FISH ANATOMY The following illustration of a largemouth bass shows some of the common internal features that are used to describe the differences between fish that are described in more detail below. As different as a man may be from a fish, both creatures share some fascinating similarities in basic structure and function. And the closer one looks, the more complex life becomes. The smallest units of life are microscopic cells, and some organisms such as an ameba are no larger than a single cell. In larger multicellular creatures, individual cells that are similar in structure and perform a specific function are grouped into tissues, and tissues may be grouped into even more complex and specialized structures called organs. These organs perform the basic bodily functions such as respiration, digestion, and sensory reception. Man and fish share such organs as the brain, stomach, liver, and kidneys. Other organs appear in different forms in different organisms; for example, the lungs in humans and the gills in fish are very different but both provide the same basic function of respiration. Finally, some organs (such as the fish's swim bladder) are simply not present in man. Below are descriptions of some of the organs identified on the above diagram, along with their functions. A number of other vital organs, such as the spleen and pancreas, may also be present but are smaller and more difficult to locate.

HEART The heart is located just below and between the left and right gill complexes. Covered in a pericardial sac the heart contains four chambers, which lie in a series. Blood moves through the heart in one circuit. Circulates blood throughout the body. Oxygen and digested nutrients are delivered to the cells of various organs through the blood, and the blood transports waste products from the cells to the kidneys and liver for elimination. A fish's heart consists of two main chambers - the atrium and the ventricle. The blood flows through veins to the atrium. It then passes to the ventricle. Muscles in the ventricle pump the blood through arteries to the gills, where the blood receives oxygen and gives off carbon dioxide.

SPINAL CORD Connects the brain to the rest of the body and relays sensory information from the body to the brain, as well as instructions from the brain to the rest of the body. The spinal cord, which consists of soft nerve tissue, runs from the brain through the backbone.

BRAIN The control centre of the fish, where both automatic functions (such as respiration) and higher behaviors ("Should I eat that critter with the spinning blades?") occur. All sensory information is processed here. The brain is an enlargement of the spinal cord and is

enclosed in the skull. fish brains are small, compared to their body shape of the brain of a trout you catch is about the size of a large pea. The brain of a fish is very different from a human brain. Fish brains have large lobes for smell and depending on the species, sight.

SWIM or AIR BLADDER A hollow, gas-filled balance organ that allows a fish to conserve energy by maintaining neutral buoyancy (suspending) in water. Fish caught from very deep water sometimes need to have air released from their swim bladder before they can be released and return to deep water, due to the difference in atmospheric pressure at the water's surface. Species of fish that do not possess a swim bladder sink to the bottom if they stop swimming. In most bony fishes the swimbladder (gas bladder) dominates the body cavity. Located between the digestive system and kidneys, this air filled sac may still be inflated if a careful dissection was conducted. The function of the swimbladder is for buoyancy regulation; primitive fish inflate the swimbladder through the gulping of air at the surface (physostomous). Advanced fish use a capillary system (rete mirabile) and gas gland connected to the blood stream to regulate the volume of their swimbladder (physoclistous). Most bony fish have a swim bladder below the backbone. This baglike organ is also called an air bladder. In most fish, the swim bladder provides buoyancy, which enables the fish to remain at a particular depth in the water. In lungfish and a few other fish, the swim bladder serves as an air-breathing lung. Still other fish, including many catfish, use their swim bladders to produce sounds as well as to provide buoyancy. Some species communicate by means of such sounds. A fish would sink to the bottom if it did not have a way of keeping buoyant. Most fish gain buoyancy by inflating their swim bladder with gases produced by their blood. But water pressure increases with depth. As a fish swims deeper, the increased water pressure makes its swim bladder smaller and so reduces the fish's buoyancy. The amount of gas in the bladder must be in-creased so that the bladder remains large enough to maintain buoyancy. A fish's nervous system automatically regulates the amount of gas in the bladder so that it is kept properly filled. Sharks and rays do not have a swim bladder. To keep buoyant, these fish must swim constantly. When they rest, they stop swimming and so sink toward the bottom. Many bottom-dwelling bony fish also lack a swim bladder.

GONADS As in all vertebrates, the re-productive organs of fish are testes in males and ovaries in females. Most fish release their sex cells into the water through an opening near the anus Testes When viable these paired structures can swell significantly and constitute up to 30% of the fish’s total body weight. Testes are usually flattened, folded around the edges and white in color. Mature individuals who are not spawning have testes with a brown color. The male organs, which produce milt for fertilizing the eggs, are much smaller and white but found in the same general location. The testes produce male sex cells, or sperm. The sperm is contained in a fluid called milt. . The males of some species have special structures for transferring sperm directly into the females. Male sharks, for example, have such a structure, called a clasper, on each pelvic fin. The claspers are used to insert sperm into the female's body. Ovaries When spawning the ovaries can constitute up to 70% of the fish’s total body weight. Ovaries can vary in color from pink, yellow or orange and usually have a tubular look. Mature ovaries are loaded with eggs contained in a clear sac. In adult female bass, the bright orange mass of eggs is unmistakable during the spawning season, but is still usually identifiable at other times of the year. The ovaries produce female sex cells, or eggs. Fish eggs are also called roe or spawn.

REFERENCES: • • • •

http://74.125.113.132/search?q=cache:pjkupAKlk3EJ:cfcc.edu/faculty/jjenkins/courses/msc276/lectures/Lab%25205%2520I nternal%2520Anatomy.doc+internal+anatomy+of+fish&cd=15&hl=tl&ct=clnk&gl=ph http://www.fish.state.pa.us/anglerboater/2002/S-O02web/internal.pdf http://library.thinkquest.org/C0124402/data/html/2/2anatomy_internal.htm http://www.iowas.co.uk/fish%20anatomy.html