One: They’re Pretty Lazy
Since fry have pretty specific requirements to support rapid growth, most nursery ponds aren’t actually used during colder months, although growing ponds may still be going strong. This means that seasonal ponds spend a fair amount of time literally chilling out. Instead of sitting around, ignored and useless, however, they can get a complete makeover so they’re primed and ready for the next year’s activities.
Two: They Love Sunbathing
Seasonal nursery ponds are actually considered preferable to year-round ponds because an annual full-pond reset prevents aquatic weeds, unwanted fish, and other pests from gaining a foothold.
After the last batch of fingerlings graduate to the next pond level, Nursery ponds are pumped out and permitted to dry out completely. Weeds, detritus, and other unwanted invaders are removed, and if a natural layer of sludge is maintained, it is allowed to dry to the point of cracking.
This dry-to-cracking step can be a significant problem if you’re using a clay or bentonite liner for your nursery pond, since even moderate dryness can damage or destroy the impermeability of your liner. Cracked clay will not reform into a water-tight barrier, and it will quickly crumble away, leaving a leaky, silty pond… or puddle.
If the natural advantages of a seasonal pond appeal to you, make sure you use a durable geosynthetic liner that’s resistant to UV rays. PVC liners can be particularly vulnerable to degradation when exposed to even indirect sunlight, and it’s expensive and time-consuming to replace them every few years. Reinforced Polyethylene Liners (RPE) are flexible, easy to install, and highly resistant to damage from exposure to sunlight. Even better, they’re rated for potable water containment (drinking water), and entirely fish-safe.
Three: They’re Clean and Well-Groomed
Growing fry need freedom to move as they feed. In fact, even their natural food sources need room to spread out. In nursery ponds, aquatic weeds that take up room without providing any advantages should be eliminated. In a seasonal pond, this is a simple process of emptying the pond completely, removing any established plants, and gently raking the sludge at the bottom, removing excess buildup. This exposes seeds and other stowaways to the drying effect of the sun.
Exposure to the sun also oxidizes troublesome chemical compounds like sulfides and facilitates mineralization of organic matter. Poisonous gases accumulated from bacterial breakdown of organic wastes are allowed to dissipate.
UV exposure and lack of water also interrupts the proliferation of aquatic weeds, eliminates viable insect larvae and kills unwanted fish populations, keeping the nursery pond in a pristine condition free of predators, diseases, and competition for resources. This is a cheap and effective way to maintain a high quality nursery pond while eliminating the need for expensive and potentially harmful chemicals.
Four: Beauty Sleep. Enough Said.
Going for the full spa experience means that while the pond bakes happily in the sun, other needs can be addressed. Dikes, embankments, trenches, and gates can be repaired or replaced, and special substrates or other environmental improvements can be installed or renewed. If water levels in the previous season indicate a potential leak, this is the time to find it and make repairs. Equipment maintenance is easy to manage at this point as well.
Eliminating Competitors
Potential competitors include fish, insects and aquatic plants who compete with fry for resources like space, oxygen and food. Aquatic plants, in particular, deplete the pond of nutrients, which would ideally go to supporting the growth of natural food sources like planktonic algae. In small ponds, larger aquatic plants can also create stress by consuming significant dissolved oxygen during the night. To offer the best advantage to your stock, it’s essential to eliminate and prevent competitors from entering the nursery pond. Without the use of chemicals, aquatic weeds can gain a significant foothold in ponds which can’t be drained, but they’re easily controlled in a thorough dry out.
Predators
Predatory species prey directly on stock. Snakes, birds, finfishes, amphibians, and crustaceans are among potential predators at the fry stage. Many aquatic insects such as beetles, dragonfly nymphs and other bugs in both their larval and adult stages compete with fry for food but also prey on them. In nursery ponds, fin fish predators are also a big problem because being larger, they have significant advantages over fry and juvenile fish. Parasites can also wreak havoc on a vulnerable young population. A full- scale summer dry out can go a long way toward eliminating these problems. Follow up chemical treatments, if needed, don’t generally need to be as concentrated.
