Ontogenetic scale cortisol, body condition, and gut content analyses of juvenile milkfish (Chanos chanos) cultured in commercial marine cage systems

To quantify chronic stress levels in milkfish cultured within a typical commercial mariculture setting, we measured ontogenetic (OG) scale cortisol of milkfish sampled from four cage systems (F1-F4) with different geographic locations and management strategies. Sampling stations were located within a mariculture area (approx. 2.2 x 0.6 km) of the Guiguiwanen Channel, Bolinao (Philippines). Each station was sampled twice (time point I and II) with an intermediate time interval of 15 days. According to Aerts et al. (2015), ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) was used to analyze OG scale cortisol. Additional to the stress-physiological data, environmental parameters (oxygen concentration, salinity) were recorded, and the gut content of the fish and the fish feed were analyzed for their carbon (C) and nitrogen (N) content, CN stable isotope signatures, presence of antibiotics (LC-MS/MS), organic matter (pyrolysis-GCMS, MetaboLights accession MTBLS1438), microbial community composition (16S amplicon sequencing, PRJEB33594, OTU table available here), and abundance of the virulence factor gene thermolabile hemolysin of Vibrio sp. (qPCR, primers: tlh-G-vibrio-0515-a-S-22: 5'-GCTGGTTCTTRGGDCAYTTCTC-3', tlh-G-vibrio-0750-a-A-22: 5'-TGGAACGCYACGGTTRTAGTTC-3'). Furthermore, the sampling took place as part of a larger sampling campaign within the ACUTE project (AquaCUlture practice in Tropical coastal Ecosystems: Understanding ecological and socio-economic consequences; funding: Leibniz SAW-2015-ZMT-4), during which also sediment microbial communities and environmental parameters were surveyed (sediment: doi: 10.1093/femsec/fiz006, SRA accession: SRP155505, doi:10.1594/PANGAEA.900758).