Lobster Farming In Freshwater

Lobster Farming In Freshwater

Beginners Lobster Culture In Cages

In Philippines lobster culture was practiced in floating cages made of nylon material. P. ornatus weighing 100-300 g stocked at 8/m2 attained 800-1.3 kg in 6-15 months. Survival for larger sizes has been more than 90% whereas in smaller juveniles of30-80 g, survival was less than 50%. Trash fish is the main feed, which is procured at US$ 0.13-0.22 per kg. Selling price of livelobster was US $ 21-31/kg; hence a wet FCR of more than 10can still be profitable.

In Vietnam, mariculture of lobsters in floating, fixed and submerged cages were practiced in protected bays or lagoons that have a good tidal flow. P. ornatus is the main species and P.homarus, P. Versicolor, P. longipes and P. stimpsoni were also cultured. Floating cage is made of nylon net material with a frame and buoy and located at a depth of 10-20 m. Wooden fixed cage is normally 20-40 sq.m and even large cages of 200-400 sq.m are also used.

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The off-bottom cage is typically about0.5 m above the seabed. This kind of cage is suitable for sheltered bays. Submerged cage is made of iron framework with a diameterof 15-16 m. The height is 1.0-1.5 m. the cage has a cover and a feeding pipe and is used for nursery rearing. Seed lobsters of about 25-30 mm TL are stocked (100- to 200 per cage) and grown to a size of about 50 g (10-12 cm TL). Lobsters are fed exclusively with either whole finfish or chopped fish or shellfish. Finfish comprised about 70% of the diet and the preferred fish is lizardfish. Feeding trash fish results in water quality problems.

The total nitrogen content in the seawater exceeded the standard level for aquaculture of 0.4 mg/L. Increase in cage farming and using fresh trash fish and shellfish has led to disease problems in some areas. Some common diseases are black gill disease, shell necrosis and red body. Treatment protocols followed are treatment with 100 ppm formalin for 3-5 minutes. Red tail disease has-been reported in spiny lobsters, which is similar to the gaffkemiain Homarus americanus. The symptoms are lethargy, reddish colour of underside of the abdomen, spreada eagle posture during late stages, poor food consumption and mortality. The bacteria enter into the body through the injury in the abdomen and multiply in the haemolymph. Isolation of the affected individuals and oral administration of oxytetracycline through feed are protocols for treatment. Antibiotic administration is possible only during the early stages of infection. The disease is highly contagious and spreads through water.

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The estimated total annual production of farmed rock lobster was about 1500 metric tones a year with a farm gate value of US$26./75/kg. The average profit margin was 50%.Therefore lobster culture is a profitable industry provided adequate seeds could be collected without disturbing the wild fishery. Suitable artificial diets are to be formulated and feeding regimes established in order to succeed lobster farming in a commercial scale. Disease protection measures should be prioritized. Cage designs should be studied for improved lobster husbandry.

Preliminary experiments in cage culture of lobsters were attempted in India by NIOT, Chennai. Floating and fixed netcages were positioned in protected areas. Fishermen fattened juvenile lobsters caught from the wild stocked in cages. However, the feasibility of large-scale farming is doubtful, as sufficient seeds may not be available for stocking when more number of people are involved. This may also result in high fishing pressure on wild fisheries and negative impact on natural lobster fisheries.

Systems Used For Fattening Lobsters

Lobsters can be successfully held and fattened in land-based holding systems provided suitable environment is provided. Critical environmental parameters include the concentration of dissolved oxygen, ammonia, nitrite and carbon dioxide.

Nitrate concentration, pH, salinity and alkalinity levels within the system are also important. In flow through systems, the main limiting factor is dissolved oxygen. The requirement of oxygen will be high during molting and soon after feeding. Both the process normally takes place during night and optimum levels of oxygen shall be maintained during night to avoid oxygen depletion and mortality.

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Oxygen related stress would adversely affect growth significantly. Unlike shrimps, lobsters are oxygen conformers and may not show any sign of low oxygen conditions, as they are capable of adjusting the metabolism even at very low levels of oxygen. Sufficient water needs to be pumped through or the water needs to be aerated to ensure lobsters are supplied with sufficient oxygen. Sudden salinity fluctuation during rains is serious situation and in such circumstances salinity, alkalinity and pH should be adjusted in a reservoir, before the water is pumped in. though lobsters can tolerate gradual changes in salinity to a limited range, sudden dilution can lead to stress, susceptibility to disease and mortality.

Indoor tanks

Two main systems are currently being used for fattening lobsters: flow-through and recirculating. In flow through systems, the water that is pumped into a tank is used only once. Water flow is to be decided based on the stocking density and feeding intensity. The incoming water is to be free of sediments and should have water quality parameters required for lobster farming.

The water should be regularly monitored to avoid wide fluctuations in environmental parameters. In recirculating systems, the majority of the water is re-used after each pass-through the tanks, first being treated to remove waste products before being returned to the tanks. Even though initial set up costs may be higher, there is an increasing interest in the use of recirculating systems.

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In recirculating systems also the main limiting factor is dissolved oxygen: however, the unionized ammonia concentration becomes increasingly important, and is probably the next important limiting factor. Ammonia should be removed from the system at a rate equal to the rate of production to maintain safe concentration.

All recirculating systems remove waste solids, oxidize ammonia and nitrite, remove carbon dioxide, and aerate the water before returning it to the fattening system.

Solid wastes can be removed by mechanical filtration, ammonia and nitrite by biological filtration and carbon dioxide by the provision of an air/water interface. The safe level of ammonia for holding lobsters is <2 mgL-1. The flow rate calculations must be adjusted according to the species held, size of the animals, the rate of feeding and the holding temperature.

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