VOORHEESVILLE — Second-graders in Timothy Mattison’s class are learning lessons in biology and geology, in math and English — all from a giant fish tank in their classroom. They are raising trout, from egg to fingerling.

The most important lesson they may be learning, though, is about the difference between wildlife and pets.

“We don’t name them,” said Mattison of the fish. “You have to be honest from the get-go...I emphasize that these are wild animals. Once they hatch — and this is true not just in our classroom but in a creek, too — if there is any difficulty, like digesting food, they die off.”

The class this year started with the usual 50 to 80 eggs. “We’re down to six fish,” Mattison said this week.

One of his students this year sent Mattison a condolence card. “It said, ‘I’m so sorry about the fish,’ It was sweet,” said the veteran teacher.

Six years ago, Mattison was intrigued when he saw a large fish tank, encased with foam boards, in an Eagle Elementary School classroom across from his son’s. “I asked the teacher why it was covered up,” he recalled.

That led him to a program sponsored by Trout Unlimited. Trout eggs raised at a fish hatchery at the State University of New York College of Agriculture and Technology at Cobleskill are delivered in October by Ron Dorn of Trout Unlimited.

“He brings us the eggs in a Mason jar,” said Mattison. “Each one is about the size of a pencil eraser. They are small and white and each has a dot, which is the eye of the fish; that’s pretty neat.”

The eggs are placed in a large fish tank in Mattison’s classroom, where the water is kept at 58 degrees, “like a creek in winter,” he said. That’s why his tank, like the one at Eagle Elementary, is covered with foam boards, for insulation.

Mattison said of the temptation to remove the boards to look at the eggs, “I always tell the kids, it’s like running a refrigerator with the door open.”

Every day, though, the boards are removed as a small group of students — they are referred to as “trout teams” — feed the fish and record their observations. “Trout Unlimited gives us what they’d eat in the creek — ground-up insects,” said Mattison, noting the smell is pungent.

The fish soon hatch with a yellow sac from the egg still attached to each one. “It’s like they have giant potbellies for a week or two; the yellow of the egg is their food source,” said Mattison.

At each session at the fish tank, the students count the fish, do a quick drawing, and record their observations. “They record in their notebooks what looks different,” said Mattison.

“Once the fish absorb their sacs, they can swim freely, and then they start eating,” said Mattison.

At that stage, the fish are most likely to die, he said. “They can have problems with eating, digesting, getting rid of waste.” In the best year of the six that Mattison’s students have been raising trout, they released 60 or 65 he said.

This year, Mattison got a permit from the state’s Department of Environmental Conservation to release six trout. One of the problems the class faced this year — a first for Mattison — was the fish had a gill disease. “There were dead ones at the hatchery, too,” he said. He had to purchase hydrogen peroxide and put 600 milliliters in the tank each day for “a couple of cycles,” he said.

“The kids ar OK,” he said of dealing with the deaths, “if you’re honest from the get-go. There are no tears. They say, ‘There’s a dead one.’ It’s very different than losing a family pet,” he said.

Mattison has taught his class from the beginning, he said, “Wild animals come from nature. They are with us just a while so we can learn, then we have to let them go.”

Mattison’s students will release the six surviving fish in the Vly Creek this month. “We get them in the creek before all the big critters wake up,” he said. On Wednesday, Mattison’s students also participated in DEC’s stocking of the Vly Creek that runs next to their school.

Two-hundred-and-fifty brown trout, each eight to nine inches long, were released as part of a DEC program that stocks trout in 314 lakes and ponds and 2,850 miles of streams across New York State.

“A surprising number of kids fish with their families,” said Mattison. He noted that the Vly Creek runs next to the elementary school, with a bridge from the school’s parking lot spanning it.

“Most kids at the school have been in the creek, playing; it goes right through the village,” he said. Mattison also said, “At the Voorheesville Public Library, you can borrow a fishing pole.”

Someone from Trout Unlimited comes out to the school and teaches the kids how to cast — “without hooks, of course,” said Mattison.

Mattison himself is not a fisherman. “I was drawn to it for environmental aspects,” he said of raising trout in his classroom. “Right now, we’re working on a dream stream project, designing the perfect habitat for trout.” Students are learning how clean the water has to be to sustain the fish, or that it can’t be too warm —shade on the sides is best.

They also have learned about the source of the creek that flows next to their school and is in its alma mater. “The source of the Vly Creek is behind Indian Ladder, in a swampy area,” said Mattison. “They learn how the water is cleaned by the boggy, swampy stuff.”

Mattison loves being a teacher. “It’s fun to come to work and be able to be a little bit goofy,” he said. “There’s an energy with kids you don’t always get with adults that I find to be honest.”

Still, he said, when the fish are let go, the fish his students raised from eggs, “There’s always a little melancholy when they release them.”

He thinks, though, that the length of time the children spend with the fish, from October till April, is good. “So many things in life are quick — poof, in, out, done,” he said. “They start with eggs and release something entirely different months and months later. They seen them go through different development stages.”

Mattison concluded, “It’s beneficial for the kids to work with something over a long period in a society where most things seem like a flash in the pan.”