Breathing :
Fish have a special mechanism in the shape of their gills for extracting oxygen from the water. This gills are positioned on either side of the head, a little gill, the gill filament and the gill lamella, are protected by the gill cover. The water enters the girls by way of the mouth valve preventing the water fro, flowing out. It leaves through the skin fold which functions as a valve at the opening at the rear of the fill cover. Any food particles are sieved out by gill rankers on the  inside of the gill lamella, in which there is a oxygen in the water in to the bloodstream of the fish.

Feeding :
Many fish are carnivorous, but they do not all prey on other fish. The most usual food consists of a variety of bottom-living and mid –water organisms, such as insect larvae, mollusks, small plank tonic crustaceans etc. Some fish live on insects which fall on the water surface. Often, when these are plentiful, they do not touch other food. Some species of fresh-water fish live exclusively on vegetation. Carp and teach to like eat water plants.    

The digestive system :
As a fish does not breathe through its nostrils or its month, but by means of its gills its gullet or esophagus leads from the mouth straight into the body cavity. Usually a fish does not chew its food, its teeth being used to grab food or prey. The food is swallowed whole. Consequently the gullet is capable of stretching to a considerable extent. Food passes next into the stomach, which is folded into a U-shape. The first half (9cardiac), which is the larger, is capable of being distended considerably by a good meal.

The second half (pyloric)  leads through a sphincter (circular) muscle, which joins the stomach and the intestine. Just beyond is the pyloric cacao, which has numerous long, narrow sacs in it, rather like the fingers of a rubber glove. There are usually more than thirty in a rainbow trout. These increase the surface or the absorptive area of the gut and sometimes aid digestion by secreting by secreting digestive juices. The length of the intestine varies appreciably from one fish to another.  It exists in the cavity of the body of the fish as a loosely coiled tube. At its far end it opens to the outside by way pf the anus, which is situated just behind the pelvic fin.

At the forward end of the body cavity is the blobbed liver with the gall bladder from which the bile duct liver with the gall baser from which the bile duct leads to the intestine. In this same area there are scattered the pancreatic tissues. The spleen is joined to the back arm of arm of the stomach.   

The digestive juices are secreted into the stomach, the pyloric caeca and the front end to the intestine. Other secretions are injected from the pancreas area. Bile, which emulsifies the oils in the food, is injected from the liver through the bile duct. These all contrive to break down the various foods into compounds that can be assimilated by the body of the fish through cells in the walls of the intestine. The unwanted, undigested remains pass out as faces through as faces through the anus.


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