For this study , 5-month-old F1 seahorses were used, born and reared at the Laboratory of Marine Ornamental Fish (LAPOM-UFSC). The fish were initially maintained at 26 °C, and the water temperature was increased by 1 °C per day using thermostat heaters . This procedure was repeated until the desired temperatures were reached . The experimental temperatures tested were 24 °C, 26 °C, 28 °C, 30 °C and 32 °C, each for 96 hours. The trials were conducted in 40 L tanks connected to a recirculating saltwater system equipped with a mechanical filter (bag), a protein skimmer and biological filters , under a 12 h light photoperiod . Five animals were used per treatment, and were fed three times a day with shrimp postlarvae (Litopenaeus vannamei , PL-25), at a density of 10 postlarvae per fish, totaling 50 postlarvae per treatment. Opercular beat rate (number of opercular movements per minute) and food intake were assessed . Prior to the first feeding , salinity was measured , remaining constant at 30 ppt in all temperature treatments, while dissolved oxygen decreased with increasing temperature : : 6.94 ± 3.84 mg/L at 24 ºC, 6.65± 5.36 mg/L at 26 ºC, 6.42± 4.17 mg/L at 28 ºC, 6.23±7.61 mg/L at 30 ºC and 6.09 ± 5.93 mg/L at 32 ºC.
Among the results obtained , the average opercular beat rate per minute (Fig. 1A) varied across temperatures , remaining at 58± 0.08 beats/min at 24 ºC, 73±0.02 beats/min at 26 ºC (control), 74±0.07 beats/min at 28 ºC, 93±0.07 beats/min at 30 ºC and 90±0.03 beats/min at 32 ºC. Food intake was lower at higher temperatures : at 30 ºC and 32 ºC, an average of 40 and 35 postlarvae were consumed , respectively, while at the remaining temperatures the consumption was 50 postlarvae (Fig. 1B).
This preliminary study demonstrates the influence and relationship of temperature on the analyzed parameters (opercular beat rate and food intake) during the 96-hour trial, which may serve as a reference for future studies involving chronic stress testing.