Tuesday, September 6, 2011

First Ocean Sunfish Necropsy of the 2011 Season

Conducted at the Seacoast Science Center in Rye, New Hampshire

On Monday morning, I received a call from Steve Engstrom, Senior Aquarist at the Seacoast Science Center in Rye, NH. Steve informed me that a small ocean sunfish had stranded on the shores of the Science Center just the other day. He had heard that NECWA was interested in ocean sunfish sightings and strandings and so had tracked me down.

I was very excited to hear about this fish and made arrangements to drive up to Rye the next day and lead a necropsy with the help of the Science Center's staff and volunteers. And Leah, one of our long-term staff members, was going to assist with the necropsy as well. This would be Leah's second ocean sunfish dissection. Her first was last December 5th when we necropsied the largest ocean sunfish we had ever seen. This fish stranded on the shores of Mants Beach in Brewster MA. This recent fish in NH would be a stark contrast to the huge carcass we examined in 2010.

Staff and volunteers looking on.

When we arrived at the Seacoast Science Center, we met Karen, Nikki and Steve as well as lots of other staff and volunteers. There must have been over 20 people in attendance as many were eager to examine this unusual fish in more detail. We noticed one other person in attendance who had very colorful boots. Time for a fun "boot" photo!

Steve and his son watching the proceedings.

Fun and wacky boots!

It was clear that this was a small fish that could be picked up by 3 or 4 people. So we decided to load the fish in my truck and bring it to Seaport Seafood Market to have it weighed. The staff of Seaport Seafood Market were wonderful and really into this very unusual and stinky fish. The carcass weighed 170 pounds and this was very exciting since this is the first accurate weight we have collected from any of our carcasses.

Weighing our ocean sunfish.

Seaport Seafood Market, Rye NH

Most of the time, we are necropsying ocean sunfish carcasses that have washed ashore on isolated beaches of Cape Cod. Getting any type of weight measurement on these carcasses is impossible since the animals are too big to carry back to the parking lot and most beaches do not allow vehicle access. So this weight was a thrill for all of us and helps to fill in a gap in our data set.

Collecting external body measurements.

Jason collecting external body measurements.

One of the Center's staff, Jason, was very interested in assisting with the necropsy in a hands-on manner. Jason has done many necropsies of seals and other marine wildlife, but never an ocean sunfish. Always great to work with someone who is really "into" the necropsies and who gets "into" the work at hand. And these fish really smell, especially after a few days on the shore.

Measuring the length of the animal.

Measuring the girth of the animal.

So with Leah and Jason by my side, we started the process of photographing the carcass and documenting any unusual external features. When we started the necropsy, we worked with the carcass with its left side up. From this side, we saw one extensive cut through the dorsal fin indicating a possible boat strike.

But when we flipped the animal over on its right side, we observed a series of propellor cuts along the dorsal surface of the animal as well as lower sections of the dorsal fin. Now it became more clear that a possible boat strike was the cause of this animal's demise. We then collected skin and muscle tissue for future genetic analysis and examined internal organs for parasites and injuries.

Carcass now left side up.

Propellor scars on the right side of the animal's body.

We collected quite a few photographs to document the propellor scars and other body features visible on the outside of the animal. After taking a number of body measurements, it was time to sample and examine the animal internally.

Testes of the ocean sunfish.

Our first order of business was to determine the sex of the fish. This animal turned out to be a boy for we found the testes just posterior to the digestive tract. As we continued to open up the animal, we realized that this carcass had only a thin layer of reticulated collagen under the thin, rough skin. The function of the reticulated collagen is not clear, but what is clear is that this material completely wraps around the body of the animal. This is why I refer to ocean sunfish as the "ocean coconut of the sea!"

We worked methodically through the animal's digestive tract and measured as many organs as possible. Staff and volunteers with the Seacoast Science Center did a wonderful job of transcribing the data and taking the majority of the photographs.

Nematodes (roundworms) in the liver.

As we continued our internal examination, we observed that the liver had quite a few nematodes (roundworms) visible on the external surface and some were clearly embedded in the inner tissue. This is not unusual for ocean sunfish as they carry a large parasite load not only internally, but also externally.

Measuring the length of the entire digestive tract.

When examining the digestive tract, we unraveled the entire tract to measure its length and boy was it long. We also cut into the stomach to look for any type of blockage and to see if we could discover and identify any prey items. As in most of the carcasses we examine, we found nothing to suggest cause of death nor did we find any jellyfish or other gelatinous critters lodged in the digestive tract.

Knife is pointing to the pharyngeal teeth of the ocean sunfish.

Pharyngeal teeth of the ocean sunfish

We examined a number of internal organs including the heart, eyes, gills and throat. In the throat, we found the pharyngeal teeth that come in a set and are located on the upper part of the throat or pharynx. These hard, pointy structure are used to help keep slimy jellyfish, ctenophores and other gelatinous critters down after swallowing. It is interesting that one set of pharyngeal teeth had 3 rows of teeth while the other had only 2 rows.

Ocean sunfish eye.

Gills of the ocean sunfish with parasites.

We were also able to collect the entire vertebral column, another first for us today. By the end of the session, we had a large collection of data, tissue samples and photographs from this carcass. All of this data will be added to the NEBShark database in an effort to better understand this the largest of all the bony marine fish.

Collecting the vertebrae.

Marine food chain model.

After we cleaned up from the necropsy, Leah and I spent some time exploring the Science Center. One of the most impressive displays is the skeleton of a humpback whale that hangs down from the ceiling. This whale is Tofu, the young female whale that was hit by a boat just a few years ago. Captain Jonny Dennen and I found Tofu floating dead on the southwest corner of Stellwagen Bank two years ago. I assisted with the necropsy of this whale that was conducted in the Bourne landfill and the bones found their final resting place in the Seacoast Science Center.

Skeleton of Tofu, the humpback whale.

It is very sad when a known humpback whale is killed offshore. We had been watching Tofu for many weeks before her death and she was a beautiful animal. Her ventral tail pattern was very white and that is how she received her name, Tofu. But seeing her skeleton displayed so majestically from the ceiling reminded me that her death was not a waste. Not only did we learn much during the actual necropsy, but we also collected a lot of tissue and organ samples for many scientists around the world. And her bones remind others of the immense size and wonder of these rare and endangered marine animals.

A model of Tofu's beautiful ventral tail pattern.

After our tour, Leah and I decided to call it a day. We were very tired, but still "flying high" after a full day of adventure and exploration. It is good to be a biologist and to find wonder in such an unusual and not well understood fish. And we made many new friends today in New Hampshire and look forward to future collaborations.