Fish hatcheries rely even more heavily on steady water quality than fish farms, due to the sensitivity of fry and fingerlings. A dip in water quality, just for a few hours, can completely ruin the chances of a batch of eggs hatching or cause stunted growth that lasts for weeks. Yet, fish are constantly ruining the very water they live in despite your best efforts to keep it clean and circulating. In addition to the constant effects of fish eating and eliminating waste into the water, these five factors all make it hard to keep water quality steady in the hatchery environment.
Influx of Fresh Water
Raceways and ponds, that are fed with a constant stream of fresh water rather than only topped off occasionally, are going to be affected by the water supply. If pollution or temperature changes happen somewhere in the supply upstream, the hatchery could be affected before the problem is even discovered. Having biofilters and treatment chambers in between the water supply and the hatchery vessels is essential, but it’s no guarantee of protection. This is one benefit that recirculating aquaculture systems have over open ones; especially when it comes to sensitive hatcheries.
High Stocking Rates
Stocking rates are particularly high in fish hatcheries because of the mid to low level survival rates when working with hatchlings and fry. It’s simply not possible to get 100% of fish fry to survive in the hatchery setting because they’re built to respond to the pressures of their environment. Yet, if you do a particularly good job at keeping fragile hatchlings alive, you can accidentally overstock your ponds and tanks when moving them to fry nursery areas. High stocking rates lead to reduced water quality due to excess waste production and competition for food. Track your stocking rates at every stage, rather than just assuming you’ll experience a standard survival rate from beginning to end.
Fluctuating Feed Levels
For the best balance of rapid growth, high water quality, and low feed costs, you’ll need to adjust how much food is given to fingerlings at every stage of growth. Following a flat feeding plan, that doesn’t account for growth rates, will quickly result in either underfeeding or water quality issues when uneaten food piles up in the ponds. Even as you carefully adjust your feeding regimen to the size and stocking rate of each pond, you’ll still find that their appetites vary due to the weather. This can alter otherwise steady water quality parameters before you notice. Overfeeding is particular likely to increase nitrogen and can leave suspended particles in the water that irritate fish gills. A complex feed management program may require more skilled labor, but it’s worth the balance in water quality.
Water Exchange Through Soil
Water exchange is one of the most overlooked issues with water quality for unlined, in-ground ponds. Unless it is lined with an impermeable polymer material, water in an earthen pond is constantly seeping out. This means that water also seeps in, mixing with the pond water and affecting the quality. Water traveling through soil and rocks picks up a lot of dissolved minerals, which end up mixed in with the water supply. It can be a lot of work to correct high mineral levels in a large pond and can put one or more of your nursery or production areas out of commission until the problem is corrected. Keeping water from exchanging through the soil is the best way to prevent this particular quality issue. A flexible liner will do the job most reliably.
Lined ponds maintain steady water quality with less work. Don’t settle for a constant battle to maintain water conditions within certain parameters, when flexible and affordable fish-safe lining materials are available from BTL Liners.
