SYNDROME-93 IN NEW CALEDONIAN OUTDOOR REARING PONDS OF PENAEUS-STYLIROSTRIS - HISTORY AND DESCRIPTION OF 3 MAJOR OUTBREAKS

Farming of Penaeus stylirostris (Mexican strain) in New Caledonia is a developing industry conducted in flow-through semi-intensive system, at 20 to 40 animals/m(2) with a theoretical extrapolated yield of 4.2 t/ha/yr. In 1995, approximately 878 t of shrimps were produced from 35 2 ha of ponds. From the 1980s to 1992, production increased progressiv ely (538 t in 1990, 648 t in 1991 and 734 t in 1992). The increase was the result of improved techniques and greater production surface area . In 1993, production decreased (621 t in 1993), then increased again in 1994 and 1995 due to increased grow out surface only. Low yields an d survival rates in 1993, 1994 and 1995 were associated with abnormal mortalities. This pathology, given the name 'Syndrome 93' appeared dur ing a period of drought and was more pronounced in winter (mid-May to mid-August). The mortalities were chronic or acute. High pond biomass and sudden water temperature drop seemed to have an impact on the deve lopment of the disease. Moribund shrimps were weak, sensitive to stres s and swam near the water surface. Shrimps were soft with dark and dul l exoskeleton and whitish muscles. Their hemolymph clotted slowly. The hemolymph of diseased shrimps was generally infected with one predomi nant strain of bacteria, Vibrio sp. The hemolymph of presumed healthy shrimp was sometimes sterile or contained variable but generally limit ed numbers of different bacteria of the genera Vibrio, Pseudomonas, Fl avobacterium and Cytophaga. Moribund shrimps exhibited classical anato mopathologic septicemic vibriosis lesions. However, numerous pycnotic hemocytes and atypical basophilic granulations were also observed in m ost tissues, especially the lymphoid organ, heart, connective tissue o f the stomach and cuticular epithelium. These basophilic granulations seemed to correspond partly to nuclear debris and partly to intracytop lasmic inclusions which are similar to those described in penaeid vira l infections ('yellow head disease', 'Taura syndrome') indicating that pathogens other than Vibrio sp. could be involved. (C) 1998 Elsevier Science B.V. All rights reserved.