Prevention in aquaculture. Part A - Prevention in cod farming
The aim of Part A was to increase the efficiency of cod farming by increasing the survival of eggs / larvae and promoting increased growth of larvae in starter feeding. The results show that the composition of the microbial flora explained the declines better than the total microbial or Vibrio counts. Extensive analysis of the microflora of aquaculture systems and larval stage results led to the determination of desirable and undesirable bacteria. Chemical measurements in cod farming at the roe and larval stages showed that little accumulation of substances took place in the farmed liquid, except at the beginning of dry feeding. The choice of additive bacteria was decided on the basis of a specific screening process and expected use in cod farming. The use of supplemental bacteria in bathing eggs and / or larvae was examined, but continuous bathing from the egg stage onwards to the larval stage usually led to better results, greater growth and vitality. The use of complementary bacteria also affected the microflora and the development of larvae shortly after hatching, which was confirmed, among other things, by measurements of proteins from the immune system. The use of supplemental bacteria in juvenile farming was investigated and indicated an increase in growth rate. It has not been possible to prove that increased disease tolerance can be achieved with the use of supplementary bacteria in juvenile farming, but there were positive indications of this. The main bottlenecks in the development of prevention methods were the live food animals, which caused a high microbial load. The development of probiotic rodents with other complementary microorganisms did not work well. Investigations into the infectious potential of the cod bacteria in cod fry showed that they did not cause any symptoms or cause death.
The aim was to increase the competitiveness and success of cod aquaculture by increasing survival and development from hatching through the larval stage. This was achieved by developing preventive methods to control important chemical and biological parameters. The results revealed that differences in microbiota composition between different larval treatments explained the success or lack thereof, better observed than total microbial or Vibrio counts of rearing water or larvae. Microbiota analysis and survival rates have hence led to the definition of desirable and undesirable bacteria, the latter being especially Vibrio sp. Assessment of selected chemical parameters was performed at pre- and posthatching periods, indicating NH3 build-up in the rearing water upon dry feeding. The selection of probiotic bacteria was based on a specific screening and their anticipated use in cod farming. Application of selected bacteria was tested for surface treatment of eggs and / or larval bathing, and the continuous use before and after hatching usually led to increased survival, growth and tolerance as well as influencing larval microbiota and immunological development. Application of selected probiotic bacteria was also tested with cod juveniles with increased growth rate. Disease resistance of probiotic-fed juveniles to fish pathogens was not confirmed. Development of probiotic rotifers proved difficult due to their high microbial load. Probiotic strains applied ip to cod juveniles were not found to be virulent