The blood is under low pressure since the it travels through a single circuit, and not a double circuit as found in reptiles, birds and mammals. Excretory System Fish remove wastes from their body via the kidneys which are located above the stomach, just beneath the backbone. Solid wastes leave the body through the anus. Ripe eggs pass out of the ovaries into the general body cavity and can completely fill the space. The eggs leave the body through the urogenital opening.
Female fishes lay hundreds, or even millions, of eggs.
The male releases milt containing sperm, over the eggs. Only a few eggs hatch to become adults. Generally, parents do not care for their young. Many newly hatched fish continue to be nourished by a ventral yolk sac, present from the egg stage. Nervous System Fish have a nervous system composed of a brain with small olfactory lobes, a cerebrum, large optic lobes and a cerebellum.