The Relationship Between An Individual's AS And Its Digestive And Locomotor Function

Different organisms have different energetic requirements to sustain life, otherwise known as the metabolic rate. Standard metabolic rate (SMR) is known as the ‘floor’ of aerobic respiration, as it is the minimum energetic cost of sustaining life. Alternatively, the maximum metabolic rate (MMR) is known as the ‘ceiling’ of aerobic respiration, as it is the maximum energetic cost of sustaining life. The aerobic scope (AS) is the difference between the MMR and SSR. AS measurements are becoming more and more important in understanding fish ecology and climate change effects. Additionally, because metabolic rates and AS vary significantly between and within species, as well as across different environments, it is important to figure out their relationship with energetically costly tasks, such as movement.

The purpose of this paper is to study more on what is very little known about the relationship between an individual’s AS and its digestive and locomotor function. Knowing the relationship will help predict the effects of other environmental constraints on similar species due to the effects of climate change. Southern catfish (Silurus meridionalis) were studied because they have different levels of food availability seasonally, which in turn is predicted to affect its AS. Fish were measured for digestive and locomotor capacity during their initial measures, after 15 days of fasting, and again after 15 days of refeeding (restoring nutrition after a period of fasting).

During the initial measures, oxygen uptake and critical locomotion (swimming) speed were measured. Then, SMR and specific dynamic action (SDA – the metabolic cost of food processing), were measured before and after the fish ate a meal respectively. After fasting for 15 days, the same variables were measured again. After refeeding, SDA, SMR, and locomotion speed were measured. SMR, SDA, and locomotion capacity were all predicted to decrease in response to fasting and increase in response to refeeding.

The results showed that oxygen consumption increased with locomotion speed during all three feeding periods. However, it reached an equilibrium in initial and fasting fish because anaerobic processes become the primary energy supply. Oxygen consumption while swimming decreased during fasting. There appeared to be very little evidence of any relationship between SMR and MMR. Overall, when fasting, locomotor and digestive capacity and metabolic rate decreased but increased after refeeding while locomotor ability decreased after the refeeding. The locomotor ability decrease was unexpected after the refeeding, especially because the fishes’ body length and mass increased after the 15 days. This can be attributed to individuals’ quick growth during refeeding (200% body mass increase) after the period of reduced growth during fasting (10% body mass decrease). More energy is being put towards the growth and less towards swimming.

In conclusion, knowing that the southern catfish places a higher priority on digestive function and metabolic requirements than locomotor function allows us to predict that similar species in similar environments will react similarly under the same conditions.