Culture of Hybrid Stripped Bass in Cages
The hybrid striped bass (Morone crysops saxatilis) is a cross between the striped bass and the white bass. The two species were successfully hybridized for commercial farming in 1967 in California. The aqua culture of this fish can be conducted in either net pens or in open ponds. A drawback to open pond culture is that ponds must be designed specifically for aquaculture, and in most cases they are not. Usually ponds are designed with irrigation, watershed conservation, livestock watering, or recreational purposes in mind. These ponds usually cannot be adequately drained or they have natural structures on their bottoms, which make harvesting difficult. However, with cage culture many of these ponds can still be used for aquaculture.
Cages or net pens are structures that enclose a number of fish in a confined area keeping them from ranging freely. This makes harvest extremely easy. The fish are dipped out of the cages or the cage itself is simply removed. Although the cage makes for a easier harvest the nature of the fish being in confined space calls for close management. Pond size is very important when considering cage culture for commercial purposes. Five acres is the recommended size for commercial culture (due to oxygen demand) although, smaller ponds can be used is mechanical aeration is used to offset the problem of oxygen depletion. Fish need oxygen to survive the oxygen they breathe is dissolved in the water. The amount of dissolved oxygen in the water is inversely proportional to the water temperature. Warmer water means lower levels of oxygen saturation, which is where problems arise. As the water temperature increases so does the metabolism of the fish. This higher metabolism causes the fish!
to consume more oxygen. If oxygen levels are low this stresses the fish, which in turn causes the fish to consume more oxygen and further reducing levels in the pond. So for a cage culture operation to be successful a high lever of oxygen saturation must be maintained. This can be done in two ways using a small number of fish on a large pond, or enhancing the ponds oxygen levels by mechanical means. The latter is what works best in intensive commercial situations. Mechanical methods such as paddlewheels, airlift pumps, or diffusers are artificial means of introducing oxygen into a pond. They simply expose more water surface to the atmosphere allowing a greater rate of oxygen transfer. Oxygen is one of the major limiting factors in determining how many pounds of fish can be produced in a given body of water. That is why in serious commercial cage culture a good oxygen meter is a valued piece of equipment.
Keeping oxygen in mind, cages can be placed any where in the pond so long as there is enough open water around and under the cage to allow water to circulate. Cages should not be set side by side so water movement is not restricted. The ideal situation is to have two cage lengths between cages. A minimum of two feet should be maintained between the bottom of the cage and the pond bottom to ensure an adequate buffer zone between the caged fish and the pond bottom, where organic waste is broken down by bacteria causing low levels of oxygen. For greatest ease in feeding and harvesting it is suggested the cages be placed along a floating dock. Pond depth is another factor in cage culture. The pond should be at least six to seven feet deep but no deeper than fifteen feet. Deeper ponds should be avoided due to water stratification. The cool water at the bottom will establish a density gradient so that normal wind action will only circulate the upper level of warm water. In deali!
ng with water temperature hybrid stripped bass require water in the range of 72 to 78oF for optimal growth.
With hybrid stripped bass it takes sixteen to twenty-four months to reach market size. The first year is devoted to fingerling production and the second to market grow out. With hybrid striped bass there are two options with respect to size when stocking. You can stock phase I fingerlings or phase II yearlings. The phase I fish are 2 to 3 inches long and about two months old. There are several advantages to stocking phase I fish. They are cheaper and there fore can be stocked in high densities. Once they reach the age the excess phase II fish can be sold off keeping the grow out density near the ponds carrying capacity. The disadvantages of phase I fish are the use of small mesh cages restricting water flow, higher mortalities, and the need to train them to take feed. Phase II fish are 6 to 8 inches long and weigh about 1/3 of a pound. These fish are healthy accept feed and are unlikely to experience significant mortalities if oxygen levels are maintained. The draw back to th!
ese fish is that they are expensive. In an intensive commercial situation phase I fish prove to be the most profitable.
The caged hybrid stripped bass are completely dependent on the farmer for food due to them being confined in cages. There fore they must be feed daily with a high quality diet. The caged fish should be fed y hand to best manage them. Feeding by hand gives instant feedback on the health of the fish. Fish should be fed twice a day once in the morning and once in the evening. Do not feed the fish after dark for this is when oxygen levels are at their lowest. Be consistent in your feeding patterns for seclude changes can disrupt the behavior patterns of the fish. The feed should be of good quality the protein amount and food size depend on the fish size. The smaller the fish the smaller the feed and the higher protein content needed. There is not a complete diet food for hybrid striped bass instead you must use trout and salmon diets. Due to this the feed rate stays between 2 to 3 percent body weight per day for ¼ pound fish decreasing as the fish reaches harvest size. Fish less !
than ¼ pound are feed 5 percent body weight per day. For Hybrid striped bass the food conversion efficiency ranges from 1.8 to2.5:1.
Hybrid stripped bass are fast attracting consumer interest in seafood markets around the country. The inland culture of Hybrid stripped bass is best undertaken in cages or net pens since it enables the use of most farm ponds with were previously thought useless foe aquaculture purposes. The cages enable the farmer to keep tight control over his fish and allow for easy feeding and harvest. With this type of culture market size fish ¾ pound to 2 pound and up fish can be achieved by the end of the second year.
