|Title||Feed intake and oxygen consumption in fish|
|Source||Wageningen University. Promotor(en): Johan Verreth, co-promotor(en): Johan Schrama; S.J. Kaushik; I. Geurden. - Wageningen : Wageningen UR - ISBN 9789461737571 - 163|
Aquaculture and Fisheries
|Publication type||Dissertation, internally prepared|
|Keyword(s)||vissen - voeropname - zuurstofconsumptie - energieopname - voer - samenstelling - energiemetabolisme - macronutriënten - visvoeding - visteelt - aquacultuur - voedingsfysiologie - fishes - feed intake - oxygen consumption - energy intake - feeds - composition - energy metabolism - macronutrients - fish feeding - fish culture - aquaculture - nutrition physiology|
|Categories||Cultured Fishes / Aquaculture Nutrition and Feeding|
In fish, the voluntary feed intake is influenced by dietary, environmental and/or physiological factors. It is well known that under hypoxia the concentration of oxygen in the water (DO) determines the feed intake of fish. However at non-limiting water DO levels (normoxia), several other mechanisms might play a role in feed intake regulation. Under hypoxia feed intake and oxygen consumption are interrelated. In this thesis we proposed the ‘oxystatic’ concept of feed intake regulation, which states that even at normoxia and in the absence of other constraints, the long term (weeks) voluntary feed intake of fish can be constrained by a set-point value of oxygen consumption. Dietary macronutrient composition affects the ‘dietary oxygen demand’ (i.e., amount of O2 consumed per unit of feed). This oxystatic concept implies that fish fed to satiation with diets differing in ‘dietary oxygen demand’ (mg O2/ g or kJ feed) will have a different digestible energy intake but a similar oxygen consumption. The validity of the oxystatic concept was assessed in two species, Nile tilapia and rainbow trout. These fish were fed diets which had large contrasts in nutrient composition (i.e., protein to energy ratio; type of the non-protein energy source (starch vs. fat); amino acid composition) in order to create contrasts in dietary oxygen demand. In all conducted studies with both species, the digestible energy intake was affected by the diet composition. However, in some studies oxygen consumption was similar and in others it differed between the diets, which respectively supports and contradicts the oxystatic concept. In all studies with both species, the digestible energy intake of tilapia and trout was negatively related to dietary oxygen demand and positively related to efficiency of oxygen utilization for energy retention. Furthermore it was observed in tilapia that the within-day variation in feed intake was affected by dietary macronutrient composition. The variation in within-day feed intake was related to pre-feeding oxygen levels. Based on the combined results, it is suggested that even at normoxia voluntary feed intake in fish is limited/determined by oxygen consumption and/or the oxidative metabolism. Overall, the oxystatic concept appears to be valid for certain conditions, but its generic application remains questionable. Yet, the oxystatic concept enables the combination of dietary, environmental and fish factors into one concept. Further it provides a conceptual insight for better understanding of feed intake regulation in fish.