Introduction

Introduction. The primary excretory organ in fishes as in other vertebrates is the kidney. In fishes some excretion also takes place in the gills where the waste materials produced during metabolism are given off..

Excretory System Functions. Collect water and filter body fluids. Remove and concentrate waste products from body fluids and return other substances to body fluids as necessary for homeostasis. Eliminate excretory products from the body..

[Audio] Excretory organs control the osmolarity and the volume of blood and tissue fluid by excreting solutes that are present in excess. Through excretion animal or organism Give out nitrogenous wastes Keep homeostasis Balance blood pH.

[Audio] Excretory organs The primary excretory organ in fishes, as in other vertebrates, is the kidney. In fishes some excretion also takes place in the digestive tract, skin, and especially the gills (where ammonia is given off). Compared with land vertebrates, fishes have a special problem in maintaining their internal environment at a constant concentration of water and dissolved substances, such as salts. Proper balance of the internal environment (homeostasis) of a fish is in great part maintained by the excretory system, especially the kidney..

[Audio] The kidney, gills, and skin play an important role in maintaining a fish's internal environment and checking the effects of osmosis. Marine fishes live in an environment in which the water around them has a greater concentration of salts than they can have inside their body and still maintain life. Freshwater fishes, on the other hand, live in water with a much lower concentration of salts than they require inside their bodies. Osmosis tends to promote the loss of water from the body of a marine fish and absorption of water by that of a freshwater fish. Mucus in the skin tends to slow the process but is not a sufficient barrier to prevent the movement of fluids through the permeable skin. When solutions on two sides of a permeable membrane have different concentrations of dissolved substances, water will pass through the membrane into the more concentrated solution, while the dissolved chemicals move into the area of lower concentration (diffusion)..

[Audio] There are three kinds of kidneys Pronephrotic kidney, Mesonephrotic kidney, and Metanephrotic kidney Pronephrotic kidney is Composed of ciliated funnels. Blood is filtered in glomerulus and enters funnel. Can be seen in shark. filters wastes from the coelom (body cavity) and excretes them to the outside. Mesonephrotic kidney is composed of This kidney filters wastes from the blood, not the body cavity, and excretes them to the outside of the body via a pair of tubes called the mesonephric ducts (also "Wolffian ducts"). The mesonephric kidney develop into the adult kidney of fish and amphibians. Can also be seen in embryo of bird reptile and mammals and Metanephrotic kidney Can be seen in Reptile, bird and mammal. filters wastes from the blood, but excretes them to the outside through a pair of new tubes, the ureters..

[Audio] Chief excretory organ Kidney Ureters Urinary bladder urinogenital apperture Kidney composed of large number of kidney tubules (generally 100-10000 no.) Each tubules known as nephron (unit of kidney) Part of kidney Head kidney Trunk kidney.

[Audio] According to Ogava(1961) marine fish kidney may divided into five types: Type-I (Clupeidae). Type-II (Marine catfishes and eel) Type-III (Most common) Type-IV (Sea horse, pipe fishes) Type-V(Lophius) Freshwater fish kidney may divided : Type-I (salmon, trout). Type-II (cypridae) Type-III (cyprinodontidae, cottidae, gasterostidae).

[Audio] The kidney of freshwater fishes is often larger in relation to body weight than that of marine fishes. In both groups, the kidney excretes wastes from the body, but the kidney of freshwater fishes also excretes large amounts of water, counteracting the water absorbed through the skin. Freshwater fishes tend to lose salt to the environment and must replace it. They get some salt from their food, but the gills and skin inside the mouth actively absorb salt from water passed through the mouth. This absorption is performed by special cells capable of moving salts against the diffusion gradient. Freshwater fishes drink very little water and take in little water with their food..

[Audio] Marine fishes must conserve water, and therefore their kidneys excrete little water. To maintain their water balance, marine fishes drink large quantities of seawater, retaining most of the water and excreting the salt. Most nitrogenous waste in marine fishes appears to be secreted by the gills as ammonia. Marine fishes can excrete salt by clusters of special cells (chloride cells) in the gills..

Head Kidney Trunk kidney Opisthonephric duct Urinary bladder Urinary Pore Ovaries Oviduct Rectum Anus Genital pore.

[Audio] Renal or malpighian corpuscle Glomerulus Bowman's capsule Renal Tubules Neck region 1st proximal segment 2nd proximal segment Distal segment Collecting duct or tubules.

Renal artery Afferent arteriole Efferent Dorsal aorta 1st Proximal Segment arteriole Glomerulus Bowman's capsule neck Distai segment Collecting duct 2nd Proximal segment.

Renal or malpighian corpuscle. Glomerulus Bowman’s capsule.

[Audio] Trunk Kidney consist of large number of (100-10000) of tubular nephrons each of which produce urine. Each tubule consist of renal corpuscles while intracellular sapce is full of lymphoid tissue function.

[Audio] Head Kidney composed of lymphoid tissue, haematopoietic, interrenal and chromaffin tissue. Few nephrons may seen in some species but renal corpuscles are absent, so it is not excretory in function.

T. S. proximal segment. T. S. distal segment.

[Audio] Dispose of metabolic wastes Regulate solute concentrations in the body Transport epithelia arranged in tubes 4 major processes Filtration, pressure-filtering of body fluids producing a filtrate (water, salts, sugars, amino acids, N-wastes) Reabsorption, reclaiming valuable solutes (glucose, salts, amino acids) from the filtrate Secretion, addition of larger molecules like toxins and other excess solutes from the body fluids to the filtrate Excretion, the filtrate leaves the system.

[Audio] There are many functions of excretory system Kidney: To remove excess salt and water To produce and remove urine which contain creatin, creatinine nitrogenous compound and urea Uric acid In marine fishes kidney remove Mg and sulphate ions and TMAO Gill: Ammonia CO2 urea.