Testing an intensive shrimp hatchery system using biofloc technology
The hatchery phase is a critical and complex first step in the commercial farming of Pacific white shrimp, and constant attention is required to produce shrimp postlarvae of the best quality possible.
The use of biofloc technology (BFT) is increasing in the aquaculture of many commercially-important aquatic species. BFT is used to intensify production and to minimize or prevent the exchange of culture water, with a consequent reduction in potential pathogens and the discharge of nutrient-rich effluents into the environment.
The objective of this study was to assess the hatchery performance of Pacific white shrimp (Litopenaeus vannamei) between the larval stages of M1 and PL5 (seven days after experimental units stocking) using a BFT system with the addition of organic carbon (molasses or dextrose) and without water exchange.
Shrimp hatcheries and BFT technology
The hatchery stage is a critical stage in the production of Pacific white shrimp, and where constant attention is required. The hatchery stage extends from the nauplii phase to the postlarva 5 (PL5) phase. At this stage, shrimp are extremely susceptible to physical, chemical and biological stressors, such as vibriosis outbreaks.
Hatchery shrimp production is traditionally performed in a predominantly autotrophic medium, with high rates of daily water exchange. At this stage, microalgae rich in polyunsaturated fatty acids are added every day, after water exchange. These microalgae not only contribute to the nutrition of the larval shrimp, but also enable the control of ammonia nitrogen levels in the tanks.
Undesirable impacts associated with such production systems – such as the discharge of large volumes of water with high levels of ammonia nitrogen and phosphorus (microalgae, feces, and uneaten feed) – may be unwanted in many coastal ecosystems and could lead to other risks. In this context, the sometimes considerable economic costs of the energy required to capture, heat, and distribute large volumes of water must be considered too.
Reducing water exchange requires control of the ammonia from protein catabolism, as it is toxic to shrimp. Ionized and non-ionized ammonia are present in the water of tanks in variable proportions that are influenced by factors such as pH, temperature and salinity. The non-ionized form of ammonia is more toxic to shrimp than the ionized form, and causes a variety of physiological damage due to its affinity for the non-polar compounds of the plasma membrane.
In BFT systems without water exchange, the ammonia control starts on the establishment of a carbon-nitrogen balance that facilitates the growth of heterotrophic bacteria, which incorporate ammonia nitrogen from the medium. This relationship is established by adding organic carbon sources (molasses, flours, sugar, and dextrose) to aquaculture media. It requires 20 g of carbohydrate, or about 6 g of carbon, to convert 1 g of ammonia nitrogen to bacterial biomass.
In BFT culture systems, chemoautotrophic and heterotrophic bacteria participate in the formation of bioflocs, which also include an aggregate of algae, fungi, protozoa, rotifers, and nematodes. Therefore, in addition to providing ammonia control, bioflocs may represent a food source in the shrimp production tanks.
The use of BFT systems in the pre-nursery and growout stages of marine shrimp aquaculture have been extensively studied. However, systematic studies with BFT without water exchange during the hatchery phase as an alternative to the standard production systems of penaeid shrimp larvae is just beginning.
In BFT culture systems, bioflocs can be a food source for the cultured animals.
See more at http://advocate.gaalliance.org/testing-an-intensive-shrimp-hatchery-system-using-biofloc-technology/