The Liver:
A normal liver is usually dark red in color, however livers of herbivorous fish may appear brownish. A healthy liver shows a uniformly red mass often containing many blood vessels. A whitish or milky liver indicates a pathological fatty condition. Under the microscope, the fat appears as small fluid spheres with dark edges. A yellow or yellowish brown liver is not capable of functioning for long; the cells die off slowly, leading to the fish's death.

The Gallbladder:
The gallbladder is transparent and filled with green fluid. It is attached to the liver, and its bile duct joins it to the intestine.

The Spleen:
The spleen of many fish is very small, with a color range from dark red to reddish black. Under a microscope it will look light red, interspersed with lighter circular areas; scattered yellow brownish clumps of cells are masses of macrophages that remove aging red blood cells from the blood. The spleen is intensely perfused with blood and thus usually is involved first when pathogens enter the bloodstream.

Internal Anatomy