Bedier, E., Le Moullac, G. Patrois, J., Aquacop
The development of the world shrimp production is dramatically slackened by the increasing emergence of pathogenic troubles. These infestations concem most of cultivated species, and are caused both by viral (IHHNV, TSV, YHV, etc.) and bacterial agents (Vibrio harveyi, V. penaeidae, etc.).
The expanded supply of high quality seed is a need to insure the profitability of the farms located in infested area. The control of such a supply is a difficult challenge insofar as animals used for the reproduction are mainly from the wild. Obviously, the definition of reliable techniques to rear captive broodstocks in ponds and to close the whole life cycle of the shrimp, is the first step towards an efficient control of the seed. Only captive broodstocks can allow pathological surveys and breeding selection for high health or resistant seeds.
The selection of either SPF or SPR lines are the alternative approaches used to constitute the captive bred stocks. In the SPF breeding program, breeders are selected according to the absence or diagnosable known pathogens, and kept in controlled conditions during several generations. High health seed produced show improved growth and survival performances under some conditions when compared to local post-larvae. Limits of this program include the reliability of wild founder stock, the need of important quarantine facilities, and the susceptibility of the post-larvae to deadly pathogens. The IFREMER experience on P. stylirostris shows that exposure of shrimps to IHHNV over many generations has resulted to disease resistant SPR broodstock. SPR post-larvae perform better than local stocks when reared in endemic areas. These results suggest that the resistance to a given disease is a heritable trait, and that a selective breeding program aimed to disease resistance is possible.
Besides the challenges against the pathogens, the efficiency of the IFREMER selection program could be dramatically increased by the use of criteria of selection based on the defense reactions occurring in the shrimp when infested. Potential criteria include the plasma antibacterial activity (antibacterial peptids), and the binding proteins, which lead the reactions of phagocytosis and the production of melanin. The variability of various defense levels (hematology, proPO system, phagocytosis, etc.) are currently being studied in connection with stress factors (molting stages, environmental and nutritional stress).
All these factors as well as bacterial challenges are recorded in SPR43 P. stylirostris crosses and sib families. This program is first being conducted using Vibrio penaeidae as challenge bacteria, owing to the identification of this pathogen in mortalities occured in New Caledonia. A multi pathogen resistant strain is expected to be created by this selective breeding program.
(IFREMER-COP, BP 7004 Taravao, Tahiti - French Polynesia)
***************