After preserving the fish, I dissect the gonads from each fish and weigh them. I preserve each gonad in formalin for future analysis. The weight of the gonads allows me to calculate the gonadosomatic index (GSI) for each fish, which is the ratio of gonad weight to somatic body weight. This particular image is an O'opu Akupa with its ventral body surface removed to reveal its internal organs. The ovaries, liver, and stomach are visible. There is a large clam shell protruding out of the anus.
The GSI is a quantitative method for the estimation of how mature or ripe the fish is. A higher GSI implies heavier gonads, which in turn implies that the fish is ripe. I correlate this data with analysis of the gonads using a microscope, in order to determine the maturation stage of each fish collected.