Studies on Application of Biofloc Technology in the Grass Carp (Ctenopharyngodon Idellus) Aquaculture
|School||Shanghai Ocean University,|
|Keywords||biofloc technology C/N grass carp growth water quality|
Grass carp (Ctenopharyngodon idellus), one of the famous "Four Major Chinese Carp", is all important economic fish in China. Its annual output is the highest of all freshwater fishes and accounts for nearly one quarter of total output, so it takes an important part in national economy. Grass carp has lots of characteristics such as strong adapt ability, wide range of feed Sources, rapid growth and delicious meat, and it can be cultured all over China. The grass carp occupies a large proportion in freshwater fish farming in China, second only to Silver carps (Hypophthalmichthys molitrix) and bighead(Aristichthys nobilis). With the rapid expansion and intensification, there is, however, also a growing concern about the ecological sustainability of fish culture. Environmental and economical limitations can hamper this growth. Especially intensive aquaculture coincides with the pollution of the culture water by an excess of organic materials and nutrients that are likely to cause acute toxic effects and long term environmental risks. For long, the most common method for dealing with this pollution has been the use of continuous replacement of the pond water with external fresh water. However, the water volume needed for even small to medium aquaculture systems can reach up to several hundreds of cubic meters per day. Biofloc technology (BFT) was recently proposed as a new approach towards more sustainable practices that lower environmental impacts and prevent diseases occurrence. BFT is the development and control of dense bioflocs in the water column by constant aeration and agitation of the water and addition of carbon sources as organic matter substrate to the pond. adding carbohydrates can improve the water quality in the pond and in addition, the bioflocs can be consumed by the cultivated aquatic organisms and thereby act as a source of diet. If the C/N ratio is increased by adding a carbohydrate source such as tapioca starch in addition to the regular feed, the increased availability of carbon allows the heterotrophic bacterial population to grow to a dense mass. Therefore, manipulation in the C/N ratio may result in a shift from an autotrophic to a heterotrophic system. BFT has been applied abroad to the breeding of Tilapia, Vannamei Shrimp, Macrobrachium rosenbergii, penaeus monodon and some other aquaculture animals achieved, however, its application in grass carp aquaculture studies have not been reported so far. This study was conducted to investigate the effects of biofloc technology on growth performance, feed utilization and of grass carp in zero-water exchange tanks. In order to further understand the bioflocs in grass carp aquaculture’s role to solve fragments and feed in aquaculture water retention problem, achieve the bait nutrient recycling, ecological and healthy grass carp aquaculture model provides new ideas. The contents were summarized as follows:1. The formation of biological floccules and the ability of removing ammonia nitrogen of bioflocs in waterWe cultured bioflocs in grass carp cement pool, and observed the structure of bioflocs under microscope and took pictures of bioflocs; We built the bioflocs system in the aquarium, the initial stage of bioflocs deposition was20ml/L, and observed the ability of removing ammonia nitrogen and ammonium chloride by adding different carbon source (glucose, sucrose and soluble starch) in this system; We took bioflocs water of1000mL with measuring cylinder and observed the bioflocs sedimentation process, at the same time,we compared the settling time. The results showed that the bioflocs commonly formed certain frame structure (mainly filamentous fungi) at first in culture, and attached by bacteria, algae and so on, and gradually increased, after bioflocs increased to a certain volume, it would unchanged or decreased. Bioflocs were made by bacteria, filamentous bacteria, protozoa, and algae and so on, it was good settleability. From the removal of ammonia nitrogen test we could see, glucose and sucrose groups of developing bioflocs could quickly reduce the ammonia nitrogen, nitrite concentration in water, at the same time, starch group of developing bioflocs could slowly reduce the ammonia nitrogen, nitrite concentration in water.2. Feasibility study of bioflocs instead of grass carp baitThis study was conducted to investigate the effects of biofloc technology on growth performance, water quality and nonspecific immunity by adding glucose in grass carp tanks. The experiment was divided into three treatments:control groups for basal feed; Treatment Groups Ⅰ. feed with the basal feed and added glucose; Treatment Groups Ⅱ. extracted bioflocs water to feed grass carp. The results showed that weight gain rate, specific growth rate in treatment groups Ⅰ and treatment groups Ⅱ were significantly lower than control groups(P<0.05). Weight gain rate, specific growth rate in treatment groups Ⅰ was significantly lower than treatment groups Ⅰ (P<0.05). Grass carps grew well in treatment groups Ⅰ and control groups, yet, Grass carp grew poor in treatment groups Ⅱ. Ammonia nitrogen, nitrite content in treatment groups Ⅰ were significantly lower than control groups(P<0.05). In short, Grass carp grew slowly with only feeding bioflocs, whether bioflocs could replace the grass carp bait need to further research.3. The influence of different C/N levels of grass carp aquacultureIn order to explore required adaptive C/N of bioflocs formation, the effects of C/N on bioflocs formation, water quality and growth performance of grass carp in zero-water exchange tanks were investigated. A locally formulated and prepared feed containing30%crude protein with C/N ratio10.8was applied to all ponds. In order to raise the C/N ratio of the feed input to15,20and25, glucose was applied separately as a source of carbohydrate in addition to artificial feed. The results showed that when the C/N was over15, the bioflocs could effectively regulate water quality, reduce water of ammonia and nitrite concentration; the biofloc volume index (FVI) was increasing with gradual increase in breeding time and stabilized in14d in the each group; With the C/N increased, the crude protein content of biofloc groups was significantly higher (P<0.05) than control groups, but there was a decreasing trend in the growth of grass carp. Serum superoxide dismutase (SOD) activity and lysozyme (LSZ) in treatment groups Ⅱ and treatment groups Ⅲ were significantly higher than control group (P<0.05), superoxide dismutase, lysozyme activity and alkaline phosphatase(AKP) in treatment groups Ⅱ had no significant difference than control group(P>0.05). Overall, when C/N was15in the biofloc technology used in the breeding of grass carp, the ratio could effectively promote the biofloc formation and reduce ammonia nitrogen and nitrite nitrogen levels.When C/N was15in the biofloc technology used in the breeding of grass carp, the ratio could effectively promote the biofloc formation and reduce ammonia nitrogen and nitrite nitrogen levels. Bioflocs were made by bacteria, filamentous bacteria, protozoa, and algae and so on, it was good settleability. Although a locally formulated and prepared feed containing30%crude protein, it could not separate as grass carp bait, because Grass carp grew slowly with only feeding bioflocs.