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Trout in the Classroom Update


The trout continue to grow and are now each about as long as a large paper clip.  Though we started with 200 eggs and over 150 hatched, that number has dwindled to a population of about 40 fry.  This is normal as a trout’s breeding strategy relies on quantity rather than quality meaning that they produce a lot of eggs but not many are expected to survive to adulthood.  In the wild, most of the young would be eaten by predators.  In our tank, the fish that grow fastest take on the role of predator.  Brook trout inhabit head-water streams where food supply from insect hatches is not always consistent.  They make it through the lean times by eating anything smaller than them that moves – including other baby brook trout!  Now that the fry are all growing at about the same rate the population should stabilize.  We have also increased their feedings to several times a day.  On the menu is a ground up fish meal that is very similar in content to store-bought fish food.

Brook trout require very clean, cold water to thrive and reproduce so we have been testing the water quality in the trout tank about once a week.  Several science classes from both the Middle and Upper School have recently visited the lab to demonstrate how to perform water chemistry analysis.  All that food that the fish are eating gets turned into waste which contains high levels of ammonia.  Since aquaria are closed systems, if the ammonia is not broken down properly, it will build up to potentially toxic levels for the fish.  We have added beneficial bacteria to the tank that help to break ammonia down into less toxic nitrites and nitrates.  Nonetheless, we still test the water and do partial water changes regularly to make sure that levels are not increasing due to issues like overfeeding.  So far our water levels have been right on the mark!