Here in Maine, it is open-water fishing season.  Superior fishing opportunities attract many tourists to this area.  Consequently, I decided I should learn a few things about fish.  Other than the fact that some fish are pretty, others are predators, and many are tasty, I confess to not knowing much about them.  

One thing I thought I knew for certain was that fish are cold-blooded.  Didn’t I answer that question correctly in sophomore year biology?

Recent studies have uncovered anomalies about this supposed fact.  The reality is that while the majority of fish are cold-blooded, at least one fish is warm-blooded, and others are hybrids.  

In 2015, the opah or moonfish (Lampris guttatus) was discovered to be a completely warm-blooded creature. This is a fish species of commercial interest found around Hawaii. Researchers with the NOAA Southwest Fisheries Science Center, who first identified this new finding hypothesized that warm-bloodedness gives the fish a competitive advantage in deeper, colder waters.  So far, the opah is the only fully warm-blooded fish identified. 

Opah or Moonfish
Image by Mgs99 on

Next, another class of fish combines the properties of both the cold and warm-blooded.  At last count, there are about 35 different species that fit this description.  These include some sharks and some tuna species.  They can warm, more or less on demand, specific sections of their bodies such as muscles and their brain.  

However, until recently, it wasn’t clear what a competitive advantage to self-warm really means.  A study conducted by a team from Trinity University suggests that the advantage translates into the ability to swim faster than competitors and predators.  Warmer muscles mean stronger muscles. These fish can swim about 1.6 times faster than their cold-blooded cousins.  

The second part of the hypothesis suggested that maybe these fish could live in waters with a broader range of acceptable temperatures, including colder areas.  However, the results suggest that this is not one of the benefits of being able to warm their body parts.  Perhaps being able to dart away is a great enough advantage!

Again, nature shows that variation has purpose and adaptability is indispensable.


More about the opah discovery —

More about the Trinity University study —

The East Coast hurricane season, which begins on June 1st, is fast approaching.  The Pacific season starts on May 15th and a named tropical storm, Andres, has already formed.  We know that storm frequency and intensity are increasing with climate change.  This is bad news for all of us who live in possible storm paths.  You are probably also familiar with stories of birds that have been blown off of their traditional course because of a storm and end up being celebrity sightings elsewhere.  However, until this news release, I had never considered the impact of hurricanes on fish such as sharks. 

The new study conducted by researchers at the University of Miami Rosenstiel School of Marine and Atmospheric Science revealed different behaviors by shark species and by location during hurricanes.  Bull sharks (Carcharhinus leucas), nurse sharks (Ginglymostoma cirratum), great hammerheads (Sphyrna mokarran), and tiger sharks (Galeocerdo cuvier) were monitored during Hurricane Matthew in 2016 and Hurricane Irma in 2017.  These were category  5 and category 4 storms, respectively. 

As a reference, bull sharks are around 11 feet in length and weigh about 290 lbs.  Hammerheads are 20 feet long and 500 lbs while nurse sharks average at 13 feet and 730 lbs.  Tipping the scales are the tiger sharks at 14 feet and 1400 lbs.   When reading the following results, weight defines the relative size of the shark more than the length. 

In the study, all four types of sharks were initially found in inshore shallow waters. This was the primary study area.  As the storms approached, most of the relatively smaller sharks left the study area for deeper water.  However, most of the large tiger sharks did not.  Counterintuitively, immediately after the storm, the tiger shark population in the shallows increased.  The research team suspects that the tiger sharks were motivated to be in the area because of the surge in their food supply. They opportunistically fed on fish and invertebrates that died during the storms.  They may be scavengers, but they still like their meat relatively fresh. 



Relative sizes of sharks —

UMiami News Release —

Scholarly publication —

One aspect of nature that fascinates me is that so often it holds the solutions to our problems, including health issues.  This weekend, I came across a Twitter post about another such application.  

Tilapia is a white fish that had its peak of popularity in the United States in the early 2000s.  It was a low-fat, high-protein dinner staple.  Then there was a flurry of publicity around environmentally harmful farming practices and concerns about its actual contributions to your health.  Tilapia is still around, but it’s no longer the star on everyone’s plate.  

Now, tilapia is having somewhat of a comeback, but not as a food.  It seems that its skins and scales have promise in the management of wounds, particularly for burns.  

Here’s why it works: Tilapia’s skin holds a large amount of type 1 collagen, the kind that is often used in beauty products for hydration and to enhance elasticity.   Next, the fish skin’s natural microbes do not pose a threat to human skin nor its microbial colonies.  Finally, the structure of the skin and scales has the flexibility and resilience needed to stay in place for days, and sometimes weeks. 

When tilapia skin was applied to a patient’s burn lesions in a clinical study, some healing (reepithelialization) was seen within 12 days.  

Consequently, tilapia skin became the first nationally studied animal skin to be registered for the use of treatment of burns.   Since then, it has been used on additional burn patients. Other studies have tried it to address diabetic skin ulcers.   Veterinarians have even applied it to their animal patients.    

While this is not a typical natural history posting, it is about a fish species.  (Actually, tilapia is a collection of nearly 100 types of cichlid fish.)  I did a fairly extensive Google search and could find no evidence of other fish species used for this purpose.   (However, there are other animal skins used.)

The post gave me cause to think.  What if tilapia didn’t exist anymore through extinction?  What other species have properties that we have yet to discover?  If we can’t care enough to save these creatures because they have value just as themselves and as part of the overall ecosystem, can we decide to save them because someday, they may save us?


Thanks to @Emma_Hollen for posting the tweet that sparked the idea for this post.  It can be seen at:


Regarding use in burn patients — Journal of Surgical Case Reports. 2019 Published online 2019 Jun 14. DOI: 10.1093/jscr/rjz181

For use in diabetic skin ulcers —

For use in veterinary applications —