FISH TELEMETRY Use of muscle activity indices as a relative measure of well-being in cultured sea bass Dicentrarchus labrax (Linnaeus, 1758) G. Lembo Æ P. Carbonara Æ M. Scolamacchia Æ M. T. Spedicato Æ R. S. McKinley Ó Springer Science+Business Media B.V. 2007 Abstract Aquaculture of sea bass is widely spread in the Mediterranean and employs a variety of husbandry protocols that need to be evaluated in terms of fish well-being. Behavioural tests can be used as operational indicators of short-term stress, because changes in swimming performance and/or muscle activity (e.g. electr- omyograms) can be interpreted as response asso- ciated with a wide variety of stressors. Diagnostic procedures, based on physiological telemetry, will thus enable appropriate mitigative strategies to be implemented to ensure the well-being of cultured fish. The objective of this study was to examine the contribution of two muscle types to the swimming activity of sea bass (Dicentrarchus labrax, L. 1758). Hard-wire technology was used to ‘fine-tune’ measures obtained using a physio- logical transmitter. Fine-tuning showed that the aerobic muscle displayed an increase in recruit- ment of muscle fibres relative to increasing swimming speed up to 0.6–0.7 ms –1 of the U crit , where the anaerobic (white muscle) activity started to exponentially augment with swimming speed, reaching up to ~7 times its initial value. Intensity of electromyogram signals were de- scribed by logarithmic (red muscle): y = 0.5922Ln(x) + 1.2251 (R 2 = 0.9906) and exponential (white muscle): y = 0.0977e 2.4723x (R 2 = 0.9845) relationships. Fine-tuning indicated that the two muscle types in the sea bass are involved in fuelling swimming activity below the U crit . Thus, scope for activity is not supported solely using aerobic metabolism, though the red muscle powers the majority of the swimming ability. Measurement of U crit displayed an aver- age value of 3.43 BLsec –1 (SE = 0.12). Associated EMG values measured during the forced swim trials using an implanted bio-sensitive radio transmitter showed that EMG’s intensity in- creased, on average, 3.2 times between 0.2 msec –1 and the U crit velocity (~1 msec –1 ). Above EMG values were fine-tuned using esti- mates obtained from direct monitoring of the red and white musculature. Overall, the results dem- onstrated that the scope for activity, previously thought to represent only aerobic metabolism, is composed of both aerobic and anaerobic path- ways. Fine-tuning of physiological transmitters to measure activity of free ranging fish can therefore Guest editors: P. R. Almeida, B. R. Quintella, M. J. Costa and A. Moore Developments in Fish Telemetry G. Lembo (&) Á P. Carbonara Á M. Scolamacchia Á M. T. Spedicato COISPA Technology & Research, Bari-Torre a Mare, Italy e-mail: lembo@coispa.it R. S. McKinley Centre for Aquaculture and Environmental Research, The University of British Columbia, Vancouver, Canada BC V7V IN6 123 Hydrobiologia (2007) 582:271–280 DOI 10.1007/s10750-006-0538-9