Aquaculture International 8: 335–348, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. Biosensors applied to biochemical fish quality indicators in refrigerated and frozen sea bass reared in aerated or hyperoxic conditions B.M. POLI 1 , G. ZAMPACAVALLO 1 , G. PARISI 1 , A. POLI 2 and M. MASCINI 3 1 Dipartimento di Scienze Zootecniche, Via delle Cascine 5, 50144-Firenze, Italia (e-mail: biancamaria.poli@unifi.it); 2 Dipartimento di Biologia Evoluzionistica Sperimentale, Bologna, Italia; 3 Dipartimento di Sanità Pubb. Epid. e Chimica Analitica Ambientale, Firenze, Italia (Received 21 September 1999; accepted 28 February 2000) Abstract. Biosensors in the detection of K 1 value (a ratio based on the changes in ATP catabolites content occurring in the muscle after death) and biogenic amines for evaluation of fish quality were tested. The K 1 value was determined, every 24 h, from 24 to 168 h after death, by HPLC and by a xanthine oxidase biosensor on 36 sea bass (Dicentrarchus labrax) stored at 1 ◦ C with ice covering. The K 1 value by biosensor and the biogenic amines by HPLC and by a diamine-oxidase biosensor were evaluated every 24 h after death or thawing until spoilage on 150 sea bass, reared under aeration or at supersaturated oxygen level and stored at 4 ◦ C, 1 ◦ C with ice covering, –20 ◦ C × 30 d and –80 ◦ C × 90 d. Refrigerated fish were evaluated by the EU sensory scheme. A close relation between HPLC and biosensor-values emerged for K 1 value. Reliable estimates by biosensor K 1 % of both EU freshness classes and the quality of frozen bass were found. Biogenic amine levels remained fairly low within the edibility period but putrescine showed more evident changes, making it promising as a spoilage indicator in frozen fish. Storage conditions markedly influenced changes after death or thawing in K 1 value or, even less, in biogenic amine levels, putrescine particularly, while dissolved oxygen in water of rearing did not. Key words: Biogenic amines, biosensors, fish quality, K 1 value, sea bass (Dicentrarchus labrax), storage conditions Introduction The post mortem biochemical changes related to the loss of fish freshness are mostly linked to autolysis, such as ATP degradation (Surette et al., 1988), and/or to microbial spoilage, such as the biogenic amines formation (Halasz et al., 1994). For this reason the changes in parameters such as the K 1 value (a ratio based on the changes in ATP catabolites content occurring in the muscle