Fish spoilage occurs due to production of metabolites during storage, from bacterial action and chemical reactions, which leads to sensory rejection. Investigating the volatilome profile can reveal the potential spoilage markers. The evolution of volatile organic molecules during storage of European seabass (Dicentrarchus labrax) fillets and Atlantic salmon (Salmo salar) slices under modified atmosphere packaging at 2 • C was recorded by solid-phase microextraction combined with gas chromatography-mass spectrometry. Total volatile basic nitrogen (TVB-N), microbiological, and sensory changes were also monitored. The shelf life of seabass fillets and salmon slices was 10.5 days. Pseudomonas and H 2 S-producing bacteria were the dominant microorganisms in both fish. TVB-N increased from the middle of storage, but never reached concentrations higher than the regulatory limit of 30-35 mg N/100 g. The volatilome consisted of a number of aldehydes, ketones, alcohols and esters, common to both fish species. However, different evolution patterns were observed, indicating the effect of fish substrate on microbial growth and eventually the generation of volatiles. The compounds 3-hydroxy-2-butanone, 2,3-butanediol, 2,3-butanedione and acetic acid could be proposed as potential spoilage markers. The identification and quantification of the volatilities of specific fish species via the development of a database with the fingerprint of fish species stored under certain storage conditions can help towards rapid spoilage assessment.Molecules 2020, 25, 1981 2 of 15 storage conditions and produce metabolites responsible for the development of off-flavors and off-odors in fish products, thus resulting in their sensory rejection [2][3][4].Modified atmosphere packaging (MAP) combined with low storage temperatures is an effective preservation technique to extend the shelf life of fishery products. Gas composition, temperature and fish species are some of the most important factors that influence dramatically the composition of spoilage microorganisms and eventually the produced metabolites [5]. Among the numerous metabolites produced during fish storage, volatile organic compounds (VOCs) have been the focus of several studies lately, for various reasons. Traditional spoilage indicators such as biogenic amines, total volatile basic nitrogen (TVB-N) and ATP degradation products exhibit weaknesses. Biogenic amines are not produced in considerable amounts in non-scombroid fish, while TVB-N increases in fish only at the late stages of storage, and cannot be used as spoilage/freshness markers [6]. ATP degradation products, which is a result of autolytic changes, affect sensory attributes only at the beginning of shelf life and not throughout storage period [7] and definitely does not determine fresh fish shelf life, which is a result of the accumulation of microbial metabolites [8,9]. A suitable spoilage marker should be a metabolite produced by the main spoilage microorganisms, exhibit a consistent profile, preferably increase during stora...