Home page » Fish anatomy » Organs of the fish

Organs of the fish

The brain

This is fairly simple in fish, when compared to other more evolved animals. The parts corresponding tosight and smell are particularly well developed, demonstrating the importanceof these two senses.

The skeleton

Obviously, this supports the fish's body, but it is less sturdy than that of a land animal, as a fish,partially reed from gravity, is "carried" by the water. Never the less,the relative fragility of the skeleton is a handicap and it is not uncommon tofind fry that emerge from their egg "twisted".

organs of a fish

The respiratory and circulatory system

Branchiae fish

This system is highly distinctive. The blood loaded with carbon dioxide is pumped by the heart to the ranchiae, where it is oxygenated. Nature has provided fish with eight branchiae(four on each side), each made up of two leaves. The total surface area of these essential organs, when spread out, would be nearly equal to that of the fish's body. The vivid red color of the branchiae is due to their abundant irrigation of blood; a darker color isa symptom of a respiratory problem. The branchiaeare fragile organs, susceptible to damage from suspended sediment or parasites,resulting in a reduced intake of oxygen, with all its unfortunate consequences.After traveling through the branchiae, the vivid red blood, rich in oxygen,irrigates the body, and the oxygengoes on to break down the food stuffs in the organs. The fish in the Belontiid family, which live in water in which the oxygen is sometimes rarefied, have a special organ for trapping atmospheric oxygen.

The digestive system

This has no special characteristics, apart from the fact that the stomach can stretch to hold large prey, especially in carnivorous fish. This is where digestion starts, and itthen continues in the intestine. With large prey the process can last severaldays, but in a tank, with artificial food, it will not take more than a fewhours.

The excretory system

This allows undigested matter to be evacuated through the anus in the form of excrement, or feces. The urine is formed in the kidneys, situated under the spinal column; it is evacuated through the urinary pore. It is worth mentioning that fishalso excrete nitrogenous substances via the branchiae. All excreted substances contain nitrogen and are toxic for animals, but ina well-balanced aquarium they are eventually converted into nitrates and thus cause no harm.

The swim bladder

Fish have a swim bladder,also known as an air bladder. This is an organ connected to the digestive system, which fills up with gas and helps fish to regulate their flotation when moving between two different types of water. They empty it to dive and fill it up when they need to come nearer the surface. Bottom-dwelling fish generally have a smaller swim bladder, or none at all, as they rarely swimin open water.

There productive organs

Males have two testicles that are linked to the vas deferens. while females have ovaries extended by the viducts. In both cases the sexual products - the spermatozoa and ova - are expelled via the genital orifice. As the fertilization of the eggs is externaland takes place in the water, there are no organs for coupling and fertilization, except in the case of live bearers.