This study was designed to profile the metabolites of Isochrysis galbana, an indigenous and less explored microalgae species. 1H Nuclear Magnetic Resonance (NMR) spectroscopy and Liquid Chromatography-Mass Spectrometry (LCMS) were used to establish the metabolite profiles of five different extracts of this microalga, which are hexane (Hex), ethyl acetate (EtOAc), absolute ethanol (EtOH), EtOH:water 1:1 (AqE), and 100% water (Aq). Partial least square discriminant analysis (PLS-DA) of the generated profiles revealed that EtOAc and Aq extracts contain a diverse range of metabolites as compared to the other extracts with a total of twenty-one metabolites, comprising carotenoids, polyunsaturated fatty acids, and amino acids, that were putatively identified from the NMR spectra. Meanwhile, thirty-two metabolites were successfully annotated from the LCMS/MS data, ten of which (palmitic acid, oleic acid, α-linolenic acid, arachidic acid, cholesterol, DHA, DPA, fucoxanthin, astaxanthin, and pheophytin) were similar to those present in the NMR profile. Another eleven glycerophospholipids were discovered using MS/MS-based molecular network (MN) platform. The results of this study, besides providing a better understanding of I.galbana's chemical make-up, will be of importance in exploring this species potential as a feed ingredient in the aquaculture industry.
Aquaculture, which involves the cultivation of aquatic animals and plants, is recognised to be an effective and vital resource-efficient food production system for supplying affordable protein to humans. Hybrid grouper (Epinephelus fuscoguttatus x Epinephelus lanceolatus) is a marine carnivorous teleost that has a high economic importance in the marine aquaculture industry particularly in countries in the Asian region. However, the vulnerability of juvenile hybrid grouper to temperature fluctuations stemming from the acceleration of climate change is regarded as one of significant threats to their market supply and a major concern for the aquaculture industry. In the present study, LCMS/MS-based mucus and sera metabolomics were used to investigate the physiological responses of juvenile hybrid grouper via their behavioural response towards temperature fluctuation stress that could be translated as indicators for either resilience or susceptibility to the stressors. Susceptible fish exhibited pronounced behavioural responses, including cessation of feeding and erratic swimming. In contrast, resilient fish displayed relatively stable behaviour, comparable to control fish, with reduced feeding as a primary deviation. A total of 36 mucus metabolites (VIP > 1) were profiled in OPLSDA in juvenile hybrid grouper subjected to temperature fluctuation stress. Among these, 20 and 16 metabolites were significantly altered (Student's t-test, p 1) were profiled, with 38 and 26 significantly altered in the susceptible (SSG) and resilient (SRG) groups, respectively. Comparative analysis between significant and resilient groups resulted in the nomination of hypoxanthine, guanosine, guanine, methionine, DL-malic acid, and glucose as potential biomarkers for susceptibility in juvenile hybrid grouper. Pathway analysis of these metabolite markers revealed that temperature stress mainly affected purine metabolism, TCA cycle, cysteine and methionine metabolism, and pyruvate metabolism. Overall, the findings of this study provide insights into the physiological regulation of juvenile hybrid grouper that are susceptible to temperature changes through their behavioural response, as well as a framework for future research.