Massachusetts Aquaculture White Paper - Aquaculture Systems and Technologies

The following information about aquaculture systems and technologies is found in Stickney (1979), Wheaton (1977), Piper et al. (1982), Brown and Gratzek (1980), and Leitritz and Lewis (1980).

Currently, four different systems account for the majority of inland aquaculture in Massachusetts: earthen ponds, tanks, raceways, and recirculation systems. Additionally, net-pen culture systems are also a possibility for limited inland use in the future. For any culture system, the main consideration in terms of growing fish is the water supply. The quantity and quality will determine not only what species can be grown and how many, but also which life stages can be cultured and by what technique. Tanks and raceways use the most water of any system for producing a given weight of fish and are reliant on a continual and clean water supply. Ponds use the least water during the course of a growing season, as only evaporative losses or outflow must be replaced, but must be monitored for gradual water quality loss due to stagnation. Recirculating systems also require small amounts of water but maintain water quality. Conditions such as water temperature, dissolved oxygen levels and water quality requirements vary widely among species. Frequently, a combination of raceways, earthen ponds and tanks are employed at the same location to accommodate the culture of a variety of species and life history stages. Additionally, the production technique employed is dependent on the size of the starting product (i.e. eggs, feeding fry, fingerlings etc.) and the desired end product (i.e. broodstock, market-size fish etc).

For more information about hydrology and water availability in Massachusetts, contact the Information Office of the U. S. Geological Survey, Water Resources Division at (508) 490-5058.

Ponds

Earthen ponds are extremely popular among Massachusetts' fish growers due in part to ease of construction, low maintenance, relatively small area requirements and ability to grow a wide variety of species. Additionally, because earthen ponds mimic nature, they may produce fish of an overall healthier appearance than other techniques. A natural supply of food is often available in earthen ponds which may lead to better fish health. Pond culture can vary from all life stages naturally occurring in a single pond to elaborate systems with discrete ponds for holding broodstock, spawning, rearing, growing and catch-out or harvest. Earthen ponds used for the production of fish are generally of two types: embankment and excavated. Embankment ponds are created by constructing a berm to impound water while excavated ponds are formed by removing soil to form a depression which is then filled by water from a stream, spring or surface run off. Provisions should be made to allow the pond to be drained.

Two major factors to consider in deciding upon embankment versus excavated pond include the topographic layout of the site location and the quality and quantity of the water supply. Depending on the surrounding topography, a combination of excavating and impounding may be necessary. The water source for the pond will in part dictate the species and numbers of fish which may be propagated. Spring fed ponds can be used to rear a wide variety of both cold and warm water species in the same pond. Earthen ponds vary in size from small, shallow, circular excavations of considerably less than one acre in surface area to large, relatively deep, rectangular ponds of several acres. Pond banks should be as steep as the soil will support to minimize the area less than one meter deep. This will minimize the accumulation of waste materials, limit growth of aquatic plants and discourage avian predation.

Raceways

Raceways are essentially rectangular troughs of varying dimensions pitched to allow a shallow stream of water to flow directly from one end to the other. Generally, raceways are constructed of concrete and are the popular method for raising trout. This type of technique is easily constructed and maintained, and due to a steady flow of water, they are able to support higher densities of fish than in ponds. Additionally, disease treatment and harvest of fish is much easier in raceways than in ponds. Their disadvantage lies however, in that they require large flows of high quality, well oxygenated water and a relatively large amount of space. Raceways are generally constructed in one of two configurations; in parallel and in series. When constructed in parallel, the water source splits to flow through multiple raceways arranged parallel to each other. The water then exits the raceways into a common outflow pipe. This type of system utilizes less space but requires high water flows to maintain the proper level in each raceway. When constructed in series, water enters the upper raceway then exits into a second raceway just downstream. This flow continues to the last raceway in the series. This design requires lower flows and less space, but can result in oxygen deficiencies between raceways and accumulation of metabolic wastes in lower raceways. The raceway concept may also be employed with natural earthen channels or by troughs with concrete sides and earthen bottoms. The dimensions of raceways will vary depending on available space and desired species, however, a length:width:depth ratio of 30:3:1 is frequently employed. Fish in raceways should be of comparable size to minimize cannibalism and harassment of smaller fish. A smaller version of the raceway trough is frequently used to incubate and hatch eggs and hold developing fry generally housed inside a building.

Tanks

Tanks essentially act as ponds but are generally constructed of concrete or fiberglass. Wood can also be used but must first be treated to prevent rotting. Concrete tanks have the advantage of being less expensive, easily constructed and formed into various shapes. Because they are heavier than fiberglass tanks, however, they tend to be permanent structures and their interior surface is not as smooth as that of fiberglass tanks. This can be overcome by the use of sealers to provide a smooth finish. Fiberglass is the most common material for fish culture tanks. Tanks of this type are light, relatively inexpensive, and inert to fresh and salt water. Like concrete, fiberglass tanks can be molded into a variety of shapes and sizes. The potential size of tanks used for fish culture is limited only by expense and engineering capabilities. Most tanks used in fish culture are circular or oval with the water inlet causing a rotary circulation. The inlet is generally above the water level in the tank to provide aeration as it enters. The water usually exits through a standpipe or bottom drain in the center of the tank. Circular tanks have several advantages over other tank shapes and raceways. Water velocities tend to be higher, feed distribution is better, they are easier to maintain, require a lower flow rate, and generally cost less to construct and install.

Net-Pen Culture

Net pen culture consists of raising fish in box shaped nets suspended in the water column. To date, most of the culture of this type in the northeast has been for salmon in shallow bays along the coast. However, recent advances in designs of floating pens have allowed the culture of trout and other species in inland waters and man made lagoons. There are two types commonly used in fish culture. The first employs a rigid structure such as pilings driven into the substrate. Nets are then stretched over the pilings to create pens. The second type is floating net enclosures anchored to the bottom. The first type is expensive to construct and limited to relatively shallow waters. In either case, good water circulation is essential since water and wind action carries away waste products and continually provides well oxygenated water.

Advantages of this technique are that fish are easily observed and harvested and relatively little space is required. Net pen culture is especially desirable in areas that cannot be drained or otherwise hamper harvesting of cultured fish. Disadvantages, however, are that because these pen structures are generally constructed in open water, they are subject to numerous factors beyond the control of the fish propagator. Wind, waves, currents and predators are just a few. Additionally, fouling caused by suspended matter in the water column adhering to the nets will dramatically increase the effect of these factors. For example, fouled nets create twice the tidal resistance than clean nets. These parameters may also change throughout the season, therefore, a thorough site analysis is recommended before this type of culture is attempted. Use of a second larger mesh net outside the confinement nets will aid in limiting predation and escapes. Because the pens are continually submerged, the material used for construction must be resistant to corrosion and weather well. Disease control is also very difficult, and labor requirements are high.

Recirculating Systems

As the name implies, recirculating systems filter and reuse all or a portion of their water. Currently, this technique is in very limited use due to its high start-up and maintenance costs. It has several advantages, however, in that this systems is highly desirable in areas where a constant water supply may be questionable or a discharge is not appropriate. Additionally, other advantages of this type of system are the ability to incorporate the growth of a second product through hydroponics and the use of settled material as fertilizer. As the technology evolves and water withdrawal and discharge requirements become more stringent, this technique is bound to see an increase in utilization. Most closed systems consist of four primary components: culture chambers, a primary settling chamber, biological filters and a clarifier or secondary settling chamber. These systems can vary in size from a compact portable unit to warehouse-sized buildings. The culture chambers are generally tanks or raceways. Multiple culture chambers may be linked to the remaining components. The effluent from the culture chambers then flows into the settling chambers. Settling chambers are designed to slow water flow to allow particulate matter to settle. Water then exits the settling chamber and enters the biofilters. Biofilters remove dissolved metabolites and convert ammonia, which is lethal to fish, to nitrate. A secondary settling chamber may be employed to remove suspended materials that may pass through the biofilter. Upon exiting the biofilters, the flow reenters the culture chambers to complete the loop. Systems which replace water at regular intervals but also recirculate a portion of their water are referred to as semi-closed systems. As a result of small losses of water due to evaporation, leakage, etc. all closed systems require replacement of small amounts of water either continually or intermittently. The obvious drawbacks to this type of system are high initial start-up costs and large amount of space required for most systems.

Click here to go back to the Table of Contents for The Massachusetts Aquaculture White Paper

Published: September 1995