Milky-white flesh syndrome in Australasian snapper (Chrysophrys auratus) in New Zealand: characteristics, causes, and consequences

Abstract The occurrence of muscle degeneration in fish populations is increasing globally and is often characterised by fillets of unusual presentation, referred to as 'jellied' or 'mushy'.These conditions have been reported to affect a range of species and locations. The causes often vary and typically impact only a relatively small number of individuals. We report on the recent emergence of a condition, milky-white flesh syndrome (MWFS), in a commercially and recreationally important species in New Zealand (Aotearoa), the Australasian snapper ( Chrysophrys auratus ; tāmure). MWFS was first observed in 2019 (affecting 5–50% of captured snapper) on the northeast coast of New Zealand, with affected fish characterised as emaciated with 'mushy' white fillets. We utilise the epidemiological triad to evaluate contributing factors and demonstrate that MWFS may result from the combined effects of dietary deficiency, environmental change, and host susceptibility. Five avenues of future research are proposed: 1. Examination of patterns and trends in affected snapper, relating to condition indices and energy deficits. 2. Examination of nutritional composition of affected snapper through the assessment of taxonomic contribution to gut content. 3. Nutritional profile of affected snapper ascertained through identification of macronutrients, fatty acids (FAs), and associated dietary markers. 4. Physiological analyses to determine significant contributors to the pathology. 5. Determination of the reversibility of this condition. These research priorities will help define causality, leading to clearer management considerations for MWFS and comparable conditions. Additionally, this work will demonstrate the impacts of environmental change in the southern hemisphere through the contribution to pathology.