So, it’s holiday season here and I’m taking some time off to recover from surgery. The fish are set up with an automatic feeder. During my one visit, they seem to be thriving and growing like crazy. I’ll post an update in January. Happy New Year!
Yes, the larger trout are eating the smallest. There is a pretty wide range of genetic variety in our trout population. The largest parr are about 2 inches, and the smallest are still under 1 inch. While I think I am providing ample trout chow for all the fish to thrive, the largest and most aggressive trout seem to disagree! Look carefully at the two pictures below. While they are a bit blurry, you can see two different views of a larger trout with a tiny tail sticking out of his mouth:
First signs of cannibalism!
Yum!
Check out this short video of our parr feeding. My they have grown!
Well, it has been about 10 weeks now since these trout were conceived. The fish now have 6-8 dark bands on each side called parr marks, and are now called parr instead of fry. These bands may have some function as camouflage for the young fish in the wild. Although the picture is a bit fuzzy, you can see these marks on some of the larger fish in the foreground:
Note parr size using ruler
If you look carefully, you can also get some sense of the genetic variety in these fish. The largest of the parr are about 1.5 inches, and the smallest around half that. As the fish get larger and hungrier, I imagine we may start to witness some cannibalism.
So, after almost a month in the tank, the fry have reached about an inch (average) in length. Notice how they aggressively “hit” the food at the surface.
It will be interesting to see how many of the approximately 100 or so fry survive over the next few months. I’m doing regular water changes, but as the fish eat more and more food, they make more and more waste.
It was a rough weekend for our trout. When I went in to check on them Saturday, I found this…
One of many dead this weekend...
…and about 19 more like him! I immediately checked the tank equipment. Seems the artificial filter system had air in the line, and had quit removing wastes and decreased flow in the tank. I quickly primed the pump on the filter, and water started moving again. I sucked the dead trout out of the tank, so their decomposing bodies would not add to the nitrogen spike surely going on in the tank. I immediately changed 5% of the water with fresh water I had on hand. I decided to avoid adding much food for the day also.
When I came in today (Sunday), I found 25 more dead trout! So, if we had an estimated 150 fry at the start of the month then we have lost about 50 total–about 30%! Is that a high mortality rate? I’m not sure since this is my first time managing trout in a 55 gallon aquarium. In the wild, trout (and many fish) have evolved in fast moving streams with little food and numerous predators so they lay hundreds to thousands of eggs–many which do not survive. So, trout experience high mortality rates in the wild.
We’re trying to maintain a simple artificial habitat for these trout, and my students are trying to maintain more complex ones called ecocolumns. These columns have two terrariums and one aquarium built using 2 liter bottles:
Artificial Ecosystems
We’ve all experienced a similar phenomenon now–a nitrogen spike. As the living things in the tank feed and produce waste ammonia, the bacteria in the water (and soil in their terrestrial chambers) convert it to nitrites and nitrates. While plants thrive on nitrates, animals find these nitrogen-rich compounds toxic. The range of tolerance for living things is often not very wide, and trout are especially fragile fish. So, I verified the spike was ammonia (instead of nitrates) and quickly did a 15-20% water change to get the stuff out of the water. I also cut back on food again, as decomposing uneaten food can also “feed” the nitrogen cycle.
Perhaps all will be ok. I’m not sure just how many trout we can sustain in a 55 gallon tank long term.
Almost all the fry have left the safety of the basket now. These two could not swim out. Apparently they have a genetic birth defect that causes a curved spine. Notice how they can only swim in circles:
A portion of any population has genetic defects that limits their survival. This is natural as mistakes (mispellings) occur in DNA as it is copied. However, man-made substances can also induce changes in DNA, or mutations. Chemicals that cause mistakes to form in DNA are known as mutagens. Click here for a recent study showing how a chemical in birth control pills is getting into rivers (via toilets) and impacting the DNA of rainbow trout. There is a growing body of research about the impact of synthetic chemicals in runoff on aquatic life.
When I walked in today, 99% of the trout had left the safety of the egg basket. The trout were lining up in the currents in the tank, and looking for food by instinct. As I sprinkle a little trout chow at the surface, the tiny trout rise to “hit” their “prey.” Check out the view of feeding behavior from underwater in this 10 second video clip:
Check back tomorrow and we’ll look at those not so lucky trout still stuck in the egg basket…
When I walked in today, at least 80% of the fry were now swimming freely in the egg basket. So, I lowered the basket to the bottom of the tank-even captured the event with underwater video:
Now the challenge is for the fish to learn to feed, and grow strong enough to fight the current. Groups of fish are starting to jockey for position in the upper currents and lower currents in the aquarium, while their slower developing cousins hide in the submerged egg basket.
Safe harbor still for some
As of today, Oct 16th, our trout are now about 30 days past fertilization. As you can see from this picture of the egg basket, many more trout have progressed to the “swim up” stage.
About 20% of our trout are swimming up now
So, these trout have exhausted their yolk sacs and are swimming up looking for food by instinct. Yesterday I sprinkled in tiny bits of trout chow, and the trout made their first attempts at learning to feed at the surface. The fish that remain on the bottom are not dead, they are just developing a bit slower–probably due to small differences in genetics. Today, we took a few of the sac fry and swimmers out to compare their anatomy under a dissecting scope. You can easily see the difference in this short video clip:
My students are testing water quality weekly, and we are trying our best to maintain a pristine mountain stream in our classroom! Check back next week for another progress report.
