Day 14- More Mahi

Noon Coordinates 23° 5'52.80"N 150°11'42.00"W

July 23, 2009
Our resident Ichthyologist, Christiana Boerger’s, account of the day:

Today we hooked 3 Mahi Mahi! This puts our total fish catch up to 7. Mahi Mahi (Coryphaena hippurus) are also referred to as Dorado or Dolphinfish. They put up a great fight when you reel them in, actually jumping out of the water. When we catch the fish, I dissect them to look for plastic in their stomach and save samples of tissue to analyze for POPs (persistent organic pollutants) later in the lab.

The dissections were particularly interesting today! I go through some simple steps to get the samples I need. First, I record the time and location of where the fish were caught. Then I take some simple measurements, standard length (the length from the tip of the closed mouth to the end of the caudal peduncle) and weight. Next comes the fun part for me, opening them up! I carefully take scissors and cut from their natural opening (anus) to the bone located in between the pelvic fins. I carefully cut out the liver and place it on a piece of tin foil which will be frozen until it can be looked at back at a lab for toxin analysis. I check out the gonads to reconfirm the sex of the fish. These are all females but none of them have had developed eggs yet. Next I remove the stomach. I make another cut to open up the stomach completely to take a look around. The last thing I do is take a muscle tissue sample of each of the fish, which is frozen along with the liver.

No plastic in the stomachs today, however, in the first Mahi, there were 3 whole fish in its stomach. I identified them to be some sort of puffer fish. You could still feel the spikes on the skin. The second Mahi had a less digested pufferfish. I was actually able to pull out the stomach of this pufferfish and found its last meal to be crustaceans (probably crabs). I found some more bones in Mahi #2’s stomach, which I identified to be from a flying fish, due to its super long pectoral fins. The third Mahi had an empty stomach, except for a couple different types of parasites which were still moving around.

We have caught small flying fish in some of our trawling nets and I am very interested to see if I will find any plastic in their stomach’s, seeing as I now know they are a part of the Mahi’s diet. So exciting from a research perspective!! Needless to say, we’ve got enough Mahi to eat for days, and Joel has made some Mahi jerky, Jeff made some Mahi poke, and the Captain is preparing a dinner tonight of what else, but Mahi sushi rolls and sashimi!!

The ORV Alguita Fish Nerd,
Christiana