Fertilizer is generally thought of as something limited to use on land. However, nursery ponds for raising fry and fingerlings are fertilized prior to the addition of new fish. The influx of nitrogen triggers the growth of both algae and phytoplankton, tiny lifeforms that even the smallest fry can eat. Fertilizing creates a change of events that establishes a food source for fry that they may rely on for the first two to three weeks of life. Even after you start feeding, some fish will only be able to eat plankton until they get larger and more mature. Proper fertilization won’t harm the fry in any way and will create just the bloom you need for feeding any stocking density.
Prior to Pond Fertilization
Before applying any commercial or locally acquired fertilizer source for your nursery pond, consider an application of agricultural lime. This powdered additive is the best option for disinfecting the surface and cutting down on pathogens without any risk to the fish. Since most fish you’ll grow for ornamental or edible use require a higher pH on the alkaline side of the spectrum, agricultural lime also plays a role in increasing the pH of the water. Finally, most fry also need a relatively high dissolved calcium level to grow rapidly and without complications. Again, agricultural lime is a good source for this mineral and helps unlock absorption of the dissolved calcium already present in the water.
Fertilizer Options for Fish Production
Old-fashioned options for fertilizing nursery ponds that are often locally available include:
- Animal manure, with chicken and cow manure serving as the most commonly used materials around the water
- Processed wastewater residues, often called milorganite
- Green manure materials like legumes and other nitrogen fixing plants
- Alfalfa pellets or rice bran that contain highly concentrated sources of nitrogen and phosphorous.
You’ll need a lot of these materials to fertilize even the smallest ponds. It can be tricky to organize transportation for these fertilizers even when they’re available in your area for an affordable price. Some of these fertilizers can introduce pathogens if they’re not properly composted or treated before being added to the pond.
Commercial fertilizers come in granular or liquid forms and are formulated specifically to the needs of the fish fry. However, they’re also far more expensive and require shipping from a central manufacturer rather than local production. They’re not available everywhere, with regions already featuring plenty of aquaculture offering more options than other areas. Liquid fertilizers can be added to existing ponds with sprayers or floating dispensers, while granulated materials tend to be added to emptied or temporarily drained nursery ponds. Some can sink and release their nutrients from the bottom within just a few days for fast preparations for the next round of fry.
Why Sludge Removal Won’t Hurt Fertility
With natural sludge and mud layers contribute some nitrogen to fuel algae and phytoplankton growth, it’s not surprising pond owners are often afraid to remove the muck in their pond. For nursery ponds, muck removal between uses is essential for rapid growth. Sludge only contributes a small amount of nutrients at the point where the newest layer of material meets the water. The rest of the muck is too compressed and contained to contribute anything useful. Instead, excessive muck uses up oxygen as part of the decomposition cycle. Regular sludge removal contributes to proper pond fertility rather than hurting it.
Whether you plan to spread manure, distribute a granulated commercial product, or spray a liquid across the surface after filling, your nursery pond needs proper fertilization. This creates the natural cycle to feed the tiniest fish until they’re large enough to eat your preferred commercial feed blends. Since you’ll need to routinely remove sludge to add new fertilizer and get its full effects, make sure you liner your nursery pond before adding any materials. Manure or pellets mixed into the soil and installed under the liner won’t contribute to the bloom of valuable feed for your fry.