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. Before we filet 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. Mahi are sexually dimorphic, which means you are able to tell the difference between male and female just by looking at them, without cutting them open to look at their gonads (sexual organs) like most bony fish. Males have a blunt, squarish head, while the females have a more feminine, roundish head. So far all of the fish we have caught have been females.

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 poke around a bit and then carefully cut out the liver and place in 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. None of them have had developed eggs yet. Next I remove the stomach. I make a cut at the top of the esophagus and completely take it out of the fish. 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, and Drew’s best guess was that they were Striped Bellied Puffers. You could still feel the spikes on the skin and see their very distinct mouth. Because the digestion process had already begun in the first fish, the insides of the pufferfish were not identifiable. 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, due to the high amount of exoskeletons found). 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 some 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 Mahi for days, and Joel has made some Mahi jerky (which is tied up on the stern and should be ready in a couple days), Jeff made some Mahi poke, (a mixture of raw fish, cabage, ginger, onions, chilli, and lemon juice), and the Captain is also preparing us dinner tonight of what else, but Mahi sushi rolls and sashimi!!

I’m hoping we catch even more fish tomorrow, especially since we are getting closer to the islands and I look forward to seeing what other species we will catch. The weather has been beautiful today and we should hopefully be in Honolulu sometime Thursday night or Friday morning. Thanks to all my friends and family reading the blog and sending emails! I miss you all so much!

The Alguita Fish Nerd,
Christiana