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Food is ingested through the mouth, but the mouth also takes in fresh water. This water is continually pumped over the gills to extract oxygen from it, and then expelled through the operculua.
The pharynx is located at the very back of the mouth, and this is where the fish grinds up food particles into smaller pieces for digestion.
The pharyngeal teeth are located on the lower surface of the pharynx. These teeth are continually shed and replaced throughout the fish’s life.
Above the teeth, on the upper surface of the pharynx, there is a hard chewing surface used to grind the teeth against.
Gill arches are bony structures that support the delicate gills. The forward projections (look like spikes) on the gill arches are called gill rakers. These gill rakers serve the purpose of straining out food and debris in order to protect the delicate gill filaments.
Gills are composed of filaments containing capillary beds for gas exchange. They allow the fish to take in oxygen and expel carbon dioxide.
The goldfish heart is two-chambered, having one ventrical and one atrium. It pumps deoxygenated blood to the gills for oxygenation, and throughout all other organ systems of the body.
The liver aides digestion by excreting digestive enzymes, stores fats and carbohydrates, and also destroys old blood cells.
The gallbladder stores bile produced by the liver.
Goldfish have no stomach for food storage, but the beginning section of the intestine, called the intestinal bulb, functions as temporary food storage in addition to absorbing lipids from food items. The second section of the intestine, called the caudal intestine, is narrower and absorbs protein from food items.
The spleen stores blood and recycles old red blood cells.
The gonads, or reproductive organs, are located underneath the swim bladder. Females have a single ovary that produces eggs, and males have paired testes for the production of milt.
Swim Bladder (Cranial Lobe & Caudal Lobe)
The swim bladder is a hollow, gas-filled sac that helps the fish maintain buoyancy. Fancy goldfish can sometimes be prone to swim bladder problems because of their modified, deep bodies. Their is a duct, called the pneumatic duct, leading from the esophagus to the swim bladder and by using this, goldfish can somewhat regulate the swim bladder by gulping air.
The kidneys filter out nitrogenous waste from the blood.
The spine provides structural support to the body, and also houses the spinal nerve cord.
The brain is where automatic functions, like respiration, and higher behaviors, like decision-making, occur. This is where all sensory information is processed.