Introduction: Daily cycles of light and temperature are powerful interrelated stimuli in the wild that entrain animals’ physiological functions and behaviour [1,2]. Being ectothermic , fish are strongly affected by water temperature and they have evolved behavioural strategy to actively choose a thermal environment that favours their physiological performance [3,4]. The aim of the present study sought to characterise the daily rhythms of thermal preference of nocturnal and diurnal fish of commercial interest using an automated system that controls and maintains a horizontal temperature gradient. The two species investigated were the nocturnal black bullhead catfish Ameiurus melas and the diurnal largemouth bass Micropterus salmoides.
Methods : We developed two separate automatic systems to control water temperature and record fish behaviour for long period. The experimental apparatus consisted in a multi-chamber tank (180×30×20cm) in which fish are freely to move across five equal compartments (30×30×20cm) . A microcontroller compatible with Arduino recorded the temperature in each compartment via a probe and switch ON/OFF a single heater in order to maintain a horizontal thermal gradient (from 18 ºC to 26 ºC). We built three replicates of the system. The two species (n=8 catfish/system; n=12 bass/system) were subjected to 14:10 h light-dark cycle (LD lasted 10 days) which was subsequently reversed to a 10:14 h dark-light cycle (DL lasted 10 days), concluding with the constant darkness condition (DD lasted 7 days ) to ascertain whether rhythms are driven by an endogenous circadian clock [5]. Fish were randomly fed once a day during the night (catfish) and light (bass) phase, and the food was evenly distributed in all chambers. During the DD period, the fish were fasted to avoid the food could become a synchronizer of their behavioural activity. To investigate difference of da ily thermal preference between species, we continuously recorded fish behaviour across the experiment by using a Raspberry Pi, remotely controlled for avoiding disturbance to fish during the experiment. Then, we performed video analysis of animal behaviour using Ethovision XT software (Noldus, the Netherlands).
Results: A. melas selected higher temperatures during the light phase and cooler temperatures during the night phase (Fig. A) , as it would experience in the wild. Conversely, the analysis of locomotor activity confirmed that A. melas is a nocturnal species, i.e. higher activity during the night phase (Fig. D). No differences emerged in their thermal preference and locomotor activity when the light-cycle changed (Fig. B, E). In DD condition, catfish showed a similar pattern those observed in the DL (Fig. C, F) suggesting that daily thermal preference and locomotor activity are endogenous. Regarding M. salmoides , data will be analysed by the end of the month . In agreement with previous works on diurnal species [6,7], we expect to find a daily rhythmicity in thermal preference displaying the same pattern as catfish. However , we expect that M. salmoides , being a diurnal species, might show an increased activity during the light phase.
Conclusion: Our results show that the thermal preference may be primarily related to endogenous systems rather than a metabolic needs for fish. Providing a thermoregulatory environment would be resemble the natural conditions in which fish live and increased their welfare [8,9 ], thus daily variation of thermal preference is an important cue to be considered when designing husbandry protocols .
1. Bertolucci, C., & Foà, A. (2004). Extraocular photoreception and circadian entrainment in nonmammalian vertebrates. Chronobiology international, 21, 501-519.
2. Bell-Pedersen, D., Cassone, V. M., Earnest, D. J., Golden, S. S., Hardin, P. E., Thomas, T. L., & Zoran, M. J. (2005). Circadian rhythms from multiple oscillators: lessons from diverse organisms. Nature Reviews Genetics, 6, 544-556.
3. Angilletta Jr, M. J., Niewiarowski , P. H., & Navas, C. A. (2002). The evolution of thermal physiology in ectotherms. Journal of thermal Biology, 27, 249-268.
4. Christensen , E. A., Norin , T., Tabak, I., van Deurs , M., & Behrens, J. W. (2021). Effects of temperature on physiological performance and behavioral thermoregulation in an invasive fish, the round goby. Journal of Experimental Biology, 224, jeb237669.
5. Herrero, M. J., Madrid, J. A., & Sánchez‐Vázquez, F. J. (2003). Entrainment to light of circadian activity rhythms in tench (Tinca tinca ). Chronobiology international , 20, 1001-1017.
6. Vera, L. M., de Alba, G., Santos, S., Szewczyk , T. M., Mackenzie, S. A., Sánchez-Vázquez , F. J., & Planellas , S. R. (2023). Circadian rhythm of preferred temperature in fish: Behavioural thermoregulation linked to daily photocycles in zebrafish and Nile tilapia. Journal of Thermal Biology, 113, 103544.
7. de Alba, G., Conti, F., Sánchez, J., Godoy, L. M., Sánchez-Vázquez, F. J., López-Olmeda , J. F., & Vera, L. M. (2024). Effect of light and feeding regimes on the daily rhythm of thermal preference in Nile tilapia ( Oreochromis niloticus ). Aquaculture , 578, 740122.
8 . Sanhueza , N., Donoso , A., Aguilar, A., Farlora , R., Carnicero , B., Míguez , J. M., ... & Boltana , S. (2018). Thermal modulation of monoamine levels influence fish stress and welfare. Frontiers in Endocrinology , 9, 717.
9 . Sanhueza , N., Fuentes, R., Aguilar, A., Carnicero , B., Mattos, H., Rubalcaba, Y., ... & Boltana , S. (2023). Behavioral Thermoregulation in Captive Fish: Molecular, Physiological, and Welfare Implications. bioRxiv, 2023-10.