By C. Greg Lutz, Guest Columnist
The goal of hatchery design, development and operation is to foster and maximize survival and output of larvae, post-larvae, fry or fingerlings. To a great extent, the factors that determine hatchery success are based on water quality and quantity, layout and design of facilities, and operational practices. Of these, only operational practices can be easily changed once a hatchery has been established. For this reason, site selection is more important for hatchery facilities than in probably any other segment of commercial aquaculture. Ideally, both surface and ground waters will be available for the site in question. Additionally, while access to utilities and major transport routes is important, this proximity to development should be balanced with a relatively undisturbed environment in the vicinity of the hatchery site.
Proximity to suitable water sources is the single most important criterion when sighting a hatchery facility. Successful hatchery operations require water with appropriate chemical characteristics, sufficient levels of oxygen, and minimal concentrations of disease organisms. While surface waters usually are well-balanced for supporting aquatic life in terms of chemical characteristics, they may harbor pathogens or parasites, not to mention pollution from various industrial or agricultural sources. Well water is typically free of disease organisms, and pollutants, but it is often devoid of oxygen as well, and may contain excessive levels of toxic dissolved gases such as hydrogen sulfide and CO2.
Most of the water supply considerations for seawater hatcheries apply equally well to freshwater facilities. Similar filtration and sterilization practices are usually required. Problems with using surface waters are similar, including not only uncertainties with regard to pollution, solids loads, and temperature, but also seasonal changes in elevation and flow. Chemical characteristics are more variable in freshwater environments, both from water body to water body and also over time. Key characteristics of concern for freshwater hatchery use include dissolved oxygen levels, temperature, nitrogenous compounds (especially ammonia nitrogen), pH, hardness, alkalinity and chloride levels.
Freshwater wells often present their own problems when used for hatchery purposes. In addition to being devoid of oxygen, they frequently have high levels of hydrogen sulfide, dissolved iron, and CO2. In some coastal areas, seasonal shifts in the depths of overlaying aquifers may result in the release of ammonia from certain types of underground mineral deposits. Taken together, these characteristics usually require vigorous aeration and, occasionally, sand filtration prior to further consideration for hatchery use. One solution is to run the inflow water through packed columns to drive off harmful gases, oxidize iron and add oxygen. Another is to pump directly into an open reservoir pond to allow natural processes to accomplish the same tasks, and then supply the hatchery from the reservoir.
In the face of increasing energy costs, not to mention biosecurity issues, water re-use is being investigated in many government and commercial hatcheries. Benefits of water re-use include conserving costs for heating or cooling water, reducing opportunities for pathogens to enter the facility through the water supply, and maintaining a more constant environment for eggs and early life stages. Successful implementation of water re-use requires a substantial investment in filtration systems and related equipment and infrastructure, but in many cases this approach may be economically justified.
Any hatchery facility should be designed to achieve efficiency while maintaining options for flexible management. Work-flow patterns should be considered when designing the facility, including water supply and drain lines. Distribution lines for air and water should be laid out efficiently, but with sufficient redundancy to isolate and respond to problems such as broken or leaking fittings. Thought should be given to incorporation of reservoir tanks, either in a centralized location or throughout the hatchery. These tanks may be designed for gravity flow or for use with back-up pumps in the event of a temporary loss of the main water supply.
Particular care must be taken to prevent any leaks on the suction side of water supply pumps, either in plumbing and fittings or in the pump itself. Small pin-hole leaks will allow air to be entrained and subsequently forced into solution under pressure. These gases in turn can result in gas-bubble disease as they leave solution in incubation and rearing tanks. Similarly, leaking fittings or unions on the outlet side of a pump can act as venturis, allowing additional air to be sucked into the system.
Most hatcheries find it necessary to raise or lower temperature of source water at various times of the year. Heating water in closed (pressurized) containment can also result in super-saturation of many gases and cause gas bubble disease. Many suitable devices with titanium surfaces are available for heating and cooling requirements, but they may be cost-prohibitive for some applications. If necessary, measures can be taken to install or construct heat-exchange devices. Polyvinyl Chloride (PVC) fittings and pipe, new fiberglass, new concrete, and many painted surfaces can all leach harmful chemicals which impact larval survival in many aquatic species. These components should be properly ‘aged’ prior to use by filling, rinsing, or steaming.
And, once water supplies and distribution are in place, a number of alarm systems may be appropriate for a hatchery depending on the complexity of the system, manpower availability, and redundancy of key components. Alarms for water levels in tanks, reservoirs or even source waters can be installed, as can alarms to monitor failure or shut-down of key systems such as water pumps.
C. Greg Lutz, has a PhD in Wildlife and Fisheries Science from the Louisiana State University. His interests include recirculating system technology and population dynamics, quantitative genetics and multivariate analyses and the use of web based technology for result-demonstration methods.