Fish biology at the marine lab

For the past three days, I spent a total of 23 hours in the lab identifying species of lantern fishes, dissecting 2 different local species of herbivorous fishes, and then examining their gut contents and digestive system.

The first day was fish taxonomy. We had a jar of 13 different species of lantern fish that were no more than 5 inches long. Most of them were only 2-3 inches long. We counted photophores, gill rakers, and fin rays. We picked out one of our identified species and will have to write a full description of the fish.

The second day was examining the digestive systems of herbivorous fish. We dissected a parore and a butterfish. First we had to remove the digestive tract to measure it and save the contents of the first segment (the stomach) and freeze them for the next day. Then we removed the skin from the cheek of the fish to see the musculature of the jaw apparatus and further down, removing the gill arches, to examine the pharyngeal structure. (Sorry if the photos seem to graphic, I thought it might be easier to show what we had to interpret this way.)

The final day we analyzed the gut contents of each of our dissected fish. We had to identify the species of algae present, which was at times quite difficult because it was partially digested. In some of them we found tiny little crustaceans that were living on the seaweed when it was ingested.

[Identified lantern fish, Hygophum hygomii]

[Dissecting a butterfish (O. pullus)]

[The greenish structure in the center of the photo is a modified to grind up food that is otherwise difficult to digest. There is a matching one on the roof of the pharynx.]