CART analysis of environmental factors, biomarkers and gill-associated virus to predict production outcomes for farmed Penaeus monodon

Gill-associated virus (GAV) is a virulent pathogen of Penaeus monodon and is one of a suite of about four viruses commonly found in prawns suffering from mid-crop mortality syndrome. Although GAV can be highly prevalent and extremely pathogenic, it does not always cause disease and has been found as a chronic infection in healthy prawns. Environmental stress caused by particularly osmotic and temperature stressors can result in viral epizootics. Therefore, classification and regression tree (CART) analysis of GAV, biomarkers (heat shock protein and ubiquitin) and environmental factors was undertaken on farms to find focal points for prediction of production and management. The order of the variation and cross-validated variation explained was relatively stable with yield (80, 41% respectively), biomass (79, 53% respectively) and average body weight (73, 55% respectively) being the most accurate whilst FCR (62, 39% respectively) and survival (59, 31% respectively) were less so. The biomarkers were less useful possibly due to the time scale of measurements involved. Of interest is that the currently recommended dissolved oxygen (DO) (4 ppm) was insufficient to prevent GAV outbreaks but DO at 4.5 ppm allowed some prawns to withstand the onslaught. It is predicted that if DO was < 4.0 ppm, then salinity maintained 32.8-38.2 ppt and temperature <= 28.8 degrees C would keep mortality loss to similar to 10%. Overnight pH should be kept to 7.6-7.8 by adequate buffering. Statement of relevance Predictive & decision model for prawn farmers when confronting gill-associated virus. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.