Necropsy Notes: General Anatomy

The heart, housed inside the pericardial cavity, is located between the pectoral fins and between each operculum (a.k.a. gill flaps). Fish hearts are two chambered compared to the four chambered hearts of humans.

Interestingly, powerful swimming fish (e.g., tunas, salmon, sharks, muskies) are not necessarily a result of their musculature make-up, but the amount of coronary circulation provided by small arteries that wrap the heart. However, not all fish have this type of circulation. Also, remember that arteries deliver oxygenated blood to the heart, whereas veins deliver DEoxygenated blood to the heart (where it can be reoxygenated). So, the coronary arteries that deliver oxygen to the heart muscle are IMPERATIVE to the performance and activity level of a fish. If these arteries become compromised (e.g., blocked) then cardiac arrest can insue. Hedrik pointed out that perhaps in warm water there is so little oxygen in the water and even less afforded to the fish during the angling event that mortalities at in warm water may be caused by heart attacks. This is purely conjecture, but is worth investigating next summer.

Fish livers are generally large (in sharks they may constitute over 1/3 of their total body weights), and the muskie's is no exception. A muskie's liver is located just below the esophagus and running along the stomach. [Far right, picture 1 and 2]. The dark colored object just left of the liver is the gall bladder.

Fish gonads are located along the top of the fish and below the backbone. In these pictures you can see this muskie is a female and full of eggs! [Update. Hedrik took a small portion of the ovaries and counted the number of eggs then extrapolated the total number of eggs using the length of the ovary. There were 606 eggs in a 29 mm/1.1 in segment of one of the ovaries. The total length of the removed ovary was 43.5 cm/17.1 in. I will forego reporting all the calculations, but there were an estimated 18,180 eggs (give or take) in this 38 in female. Scott and Crossman (1983) reported a range of 6,000 to 265,000 eggs in adult muskellunge. Hedrik's estimate falls well within the reported range!]

The creamy white tissue below the ovaries and lining either side of the pink tissue (intestine) are fat deposits.

When we caught the fish I noticed a bulge in its stomach, and during the necropsy had a chance to find out what was inside it! Perhaps not surprisingly, it was another white sucker of nearly identical size as the one we used to catch the muskie with. The sucker already in its stomach appeared to be extremely fresh, with hardly any signs of decomposition.