Ambient temperature is a key factor influencing feeding processes in fish. Therefore, adjusting feeding strategies to temperature is essential for efficient and sustainable aquaculture. This study evaluated the effect of 15 °C and 21 °C—representing average winter and summer seawater temperatures in Ensenada, B .C., —on gastric emptying, plasma glucose, digestive enzyme activity, and the expression of appetite-related genes in juvenile Morone saxatilis reared in seawater.
The bioassay was conducted in two RAS , each with three 500 L tanks (26 fish per tank; 11.4 ± 0.2 g). One system was maintained at 15 °C and the other at 21 °C for eight weeks, with fish fed a commercial diet at 4% of their biomass. Following a 48-hour fasting period, fish were fed to apparent satiation and sampled every 3 hours over a 24-hour period (9 time points; 3 fish per time point). Physical and chemical water parameters were monitored.
Fish were anesthetized, measured, weighed, and sampled for blood and tissues (brain, liver, stomach, pyloric caeca, midgut, distal intestine). Data were analyzed using t-tests, repeated measures ANOVA, and nonlinear regression (p < 0.05). Temperature, time, and their interaction significantly influenced growth, remaining stomach feed (RSF%), plasma glucose (GLU), and the activity of trypsin, L-aminopeptidase, and lipase (Table 1). At 21 °C, striped bass exhibited greater growth (249.1%) and faster gastric emptying (60% evacuated at 4 h), compared to 15 °C (93% growth; 60% evacuated at 13 h) (Figure 1). Glucose peaked earlier (5 h post-feeding) and at lower levels (195 mg/dL) at 21 °C, versus a later (17 h) and higher peak (470 mg/dL) at 15 °C. Enzymatic activity peaked earlier (<12 h) at 21 °C and later (>12 h) at 15 °C. Analysis of appetite-related gene expression (leptin and orexin) is ongoing and will be presented.