Background/Aims
Australasian snapper (Chrysophrys auratus; tāmure) is one of the most abundant and valued coastal fish species in New Zealand (Aotearoa). Since 2019, snapper from the northeast coast of New Zealand have exhibited milky‑white flesh syndrome (MWFS), characterised as emaciated with 'mushy' white fillets. Although chronic starvation has been proposed as a potential cause, the nutritional profile of affected individuals has not been thoroughly examined. Consequently, key differences in the nutritional profile of sampled snapper were assessed in fish categorised into three groups (i.e., Healthy, Intermediate MWFS, and Severe MWFS).
Methods
Fulton's condition factor (K), moisture content (MC), ash-free dry weight (AFDW) and macronutrients (i.e., lipid, carbohydrate, and protein content) were examined. Additionally, fatty acids (FAs) and derived trophic markers (FATMs) were quantified. These analyses provide insight into the nutritional decline of snapper with increasing MWFS severity.
Results
Snapper with Severe MWFS exhibited significantly lower lipid and carbohydrate content, along with reduced K values, compared to Healthy individuals. In contrast, MC was significantly higher in fish exhibiting MWFS. Absolute concentrations of all FA classes declined with increasing MWFS severity; however, FA composition revealed relative conservation of polyunsaturated FAs at the expense of saturated and monounsaturated FAs. The FATMs further suggested dietary shifts: Healthy individuals showed higher contributions from autotrophic flagellates, whereas snapper with Severe MWFS exhibited increased reliance on microbial or detrital food sources.
Discussion
Overall, the biochemical composition shows progressive nutritional decline and greater trophic distance from primary producers with increasing MWFS severity. This pattern is consistent with food limitation and utilisation of lower‑quality food resources, potentially driven by altered ecological conditions. These results underscore the broader role of environmental change in mediating nutrition-related pathologies in marine species and highlight the need for integrated ecological and physiological monitoring to understand emerging disease syndromes.