Fish breeding and raising facilities tend to feature many rearing ponds of different designs and layouts. Rearing ponds can be designed to grow fry, fingerlings, or even mature fish as the final goal depending on the size, depth, and water quality. Nursery ponds are a subset of rearing ponds that house fish during the most delicate and difficult stages of growth. Extra time and money spent on nursery pond design pays off in the long run with much larger yields during each growth cycle thanks to stable conditions. Building a nursery pond requires you to choose a fish or mix of species first so you can tailor your design to their specific mix of needs.
Raising Fry to Fingerlings
Nursery ponds are specifically designed to raise fry that are a few days old until they’re large enough to be considered fingerlings. Fry are moved from highly controlled and indoor hatchery tanks into outdoor nursery ponds to give them space to grow and access to a properly sized food source. Most nursery ponds are fertilized prior to the arrival of a new batch of fry so there are plenty of plant and microorganism food sources suspended in the water. Triggering algae and freshwater plankton growth is usually something to avoid in a fish pond, but it’s an essential part of setting up a thriving nursery pond.
Designing Ponds with Fish in Mind
From ornamental koi that can take months to grow an inch to rapidly growing warm water food fish species, you have many options for stocking a nursery pond. Yet the exact conditions preferred by each species, right down to the water temperature, pH level, dissolved oxygen, and more, vary so much that what one fish loves may kill off another type. Putting trout in a pond designed around the needs of tilapia will only lead to slow fry growth, extensive losses, and increased rates of cannibalization among the growing fish. Settle on a single species or a mix of fish with complementary requirements before designing a nursery pond.
The Seasonal Nature of Nursery Ponds
Most nursery ponds are only used for a few months out of each year when outdoor conditions are right for growing fry to fingerlings. These kinds of ponds are rarely used during fall or winter in cooler climates, even if other rearing tanks and ponds in the facility are heated and used year-round. If you want to use your nursery pond year round, it’ll need extensive heating since fry are particularly sensitive to temperature fluctuations. Insulation installed under the liner and above the soil can also help protect your fish from temperature changes. Many nursery ponds are drained at the end of each active season for easy cleaning and other benefits.
Preventing Unwanted Fry Behavior
Nursery ponds installed outdoors and in the ground are often chosen to prevent the unwanted fry behaviors that crop up during tank rearing. Fiberglass and plastic tanks can trigger a number of problems that reduce the population or slow the growth rate. The environment of the nursery pond is more natural and provides a buffer against stress-induced behaviors. For example, walleye and catfish fry are known to cling to the sides of hatching and rearing tank walls. This is because the light-colored material or finish used for these tanks reflects a lot of light, confusing the natural behavior of the fry. The sloped walls, natural layer of sludge, and dark colored liners used for nursery ponds prevents clinging and other behaviors that reduce feeding activities.
High Water Quality and Volume
Despite starting out so small, fry need nursery ponds sized to their total finished size as fingerlings. If you plan to harvest catfish fingerlings at 4 inches for direct transfer to lakes and ponds, you’ll need a water volume and stocking rate based on that final size. Even fish species that can handle less than ideal water quality will need a highly balanced environment when in the fry stage of growth. Multiple filtration units, low stocking rates, and backup sensors to detect temperature changes or oxygen loss protect you from sudden losses when conditions change.
Cage vs Open Pond Culture
Nursery ponds tend to be designed so that the entire body of water is used for fry rearing. If you have access to a large or flowing body of water that can be used for aquaculture, setting up a cage or net system may make more sense. Fry rearing cages are made from a fine mesh that allows water to travel freely through the pen without letting the tiny fish escape. The pen can be expanded as the fish grow. While using a body of water provides a constant supply that needs no filtration, the water may still not have the quality measurements needed for your chosen fish species. Ponds offer better control of water supply and therefore the resulting water quality. There’s also need to move or resize a pond when it’s built from the beginning to hold the desired amount of finished fingerlings. If you’d like to combine systems, you can always separate different ages or species of fry within a larger nursery pond with net cages.
A properly performing nursery pond can handle fry as young as two to three days old and bring them to the fingerling stage of maturity in as little as three weeks. Thanks to an open water surface, perfect conditions for growing a natural supply of food, and relatively low maintenance requirements, open ponds are ideal for raising fry of both ornamental and edible fish species.