Did you know trout burp?!

 Hi friends!

Check out this video of a trout burping and keep reading to find out how it works!

Ever wondered how your trout can move up and down in their tank or in a lake? It may seem as simple as them just swimming up or down, but the physics are actually much more complicated. Water has different densities and more or less pressure at different depths, so your trout has to adjust as it moves through a water column (if you think about your body of water as an excel sheet, the column is the up and down dimension).

Your trout moves through the column of water by adjusting its buoyancy (fancy word for how much it floats or sinks). To adjust to different depths of water and change between them, your trout has a swim bladder. This swim bladder can fill with air to make the trout more buoyant, so that it floats, or less buoyant, so that it sinks. Swim bladders can be found in trout and salmon and are connected to their throat, so they can pull air into and out of them as they breathe (it's a little like you closing off your lungs when you swallow so you don't pull liquid into them). To release the air the trout burps, like you would after drinking a lot of soda.

Sometimes when a trout is caught in deep water it doesn't have enough time to adjust its swim bladder before it comes to the surface, when that happens you can have to manually burp the trout, as in the video above. If the trout doesn't burp and you release it, it will float belly up if it has too much air in its swim bladder, and can die before it's able to release the air.

You can check out a trout burping in person next time you're fishing with your family!

Wild Winter Baby Trout

We've been observing our trout hunting and eating zooplankton in captivity, but what about all the baby trout in the wild? Will they have the upper fin in hunting and competing for food when we release our captive trout? Is a winter stream environment a nurturing habitat for baby trout? Let's find out!

A baby wild trout has about 5 months of life in its stream habitat by this time in March and is known as a trout "fry" or "parr." Check out this cool video to see what a brook trout parr looks like at this time of year!

Upper Treman trout stream in May 2020.

Here are some cool facts about wild trout parrs and how they grow up: 

1. A wild trout parr will be smaller than a trout parr raised in captivity. This is because growing up in the wild is typically colder than growing up in a tank, the water can even be a temperature that would normally cause water to freeze if the stream is running fast enough! The colder the water a trout grows up in, the slower the trout will grow. 
   

2. 

   Stonefly larvae in June 2020.

   A wild trout parr starts hunting almost right away as soon as it can swim, and sometimes even before it can swim! While our captive trout learn to come up to the surface of the tank and beg for food, a wild trout looks for its food at the BOTTOM of a stream. This is called BENTHIC feeding and means that trout grow up mostly eating stonefly, mayfly, and caddisfly larvae that can be found hiding among the rocks of healthy streams. 
   
3. A wild trout parr will hunt and eat zooplankton, just like we watched with our captive trout in our recent feeding experiments! Wild parrs don't typically eat Daphnia (the zooplankton we fed our trout), but they do eat a different species of zooplankton... known as copepods. In fact, a common copepod that trout like to eat is called a calanoid and might look like a Plankton you've seen before (hint: Spongebob).
   

   

   Calanoid, a microscopic zooplankton.

So what do you think? Who has the upper fin? A trout that has grown up hunting and spent its whole life in the wild, or a larger trout that doesn't have as much experience hunting or hiding among the rocks? 

Trout Feeding Results!

We're almost done with live feeding experiments this year! Let's take a look at what we've found so far and some questions we might still have:

Based on the graph above we can see that we know our trout will eat daphnia, BUT each trout at each school behaves a little differently. These are cumulative (adding all together) numbers from each school, so we can see that there are particular times where trout find the daphnia and eat them right away. This is cool, but because the numbers are all together we miss how many trout didn't eat any at all or ate more than the number of daphnia we thought were introduced to that trout's beaker. 

Marina with South Hill trout experiments last week! 

At South Hill the other day: "My trout didn't eat anything at all!," proclaimed an upset 4th grader. She continued, "it didn't even move!" The other students at her table and the teacher agreed, the trout hadn't even moved. 

Following our classes it's not uncommon to see a complete lack of interest in the daphnia from at least one trout per classroom (South Hill that day had 5). Our students at South Seneca and Fall Creek came up with some ideas for changing the experiment to find out WHY some trout don't eat. 

"We could use a bigger container or put 2 or 3 trout together," suggest the 5th graders at South Seneca. Their observations led them to believe that perhaps the trout would eat more given a larger space or some companions to compete against. We tested this at Caroline, where the 4th graders poured their trout and any leftover daphnia back into the tank and observed with exclamations "Wow look how fast their eating!" and "That trout must've been really hungry!" 

Newfield trout feeding with DCL pre-COVID!

The 4th graders at Fall Creek had other ideas: "We could use a mirrored box," one student suggested, "that way the trout can't see us, but we can still observe the trout." This student thought maybe having everyone observe the trout made them eat less, no one likes eating with someone staring at them. Other suggestions included trying different food besides daphnia - things like smaller fish, ants, bugs, crushed crayfish, seaweed, or even fish lures - to see if perhaps daphnia just weren't motivating enough to make a good trout feeding experiment. 

All these great observations led to a complex scientific discussion. When we broke down watching the trout eat and how they behaved we came up with that we knew the trout would eat daphnia, but not WHY or WHEN or HOW QUICKLY. Through these observations we were able to conclude that our trout should be able to hunt and find food when released into a stream environment, but not all would survive the same and some might struggle to meet their basic needs after growing up in captivity.