Constraints on Energy Intake in Fish: The Link between Diet Composition, Energy Metabolism, and Energy Intake in Rainbow Trout

Abstract

The hypothesis was tested that fish fed to satiation with iso-energetic diets differing in macronutrient composition will have different digestible energy intakes (DEI) but similar total heat production. Four iso-energetic diets (2×2 factorial design) were formulated having a contrast in i) the ratio of protein to energy (P/E): high (HP/E) vs. low (LP/E) and ii) the type of non-protein energy (NPE) source: fat vs. carbohydrate which were iso-energetically exchanged. Triplicate groups (35 fish/tank) of rainbow trout were hand-fed each diet twice daily to satiation for 6 weeks under non-limiting water oxygen conditions. Feed intake (FI), DEI (kJ kg−0.8 d−1) and growth (g kg−0.8 d−1) of trout were affected by the interaction between P/E ratio and NPE source of the diet (P<0.05). Regardless of dietary P/E ratio, the inclusion of carbohydrate compared to fat as main NPE source reduced DEI and growth of trout by ∼20%. The diet-induced differences in FI and DEI show that trout did not compensate for the dietary differences in digestible energy or digestible protein contents. Further, changes in body fat store and plasma glucose did not seem to exert a homeostatic feedback control on DEI. Independent of the diet composition, heat production of trout did not differ (P>0.05). Our data suggest that the control of DEI in trout might be a function of heat production, which in turn might reflect a physiological limit related with oxidative metabolism.

Feeding rainbow trout with a lipid-enriched diet: effects on fatty acid sensing, regulation of food intake, and cellular signaling pathways

“…Feeding the high-fat diet, however, did not decrease the amount of food intake (either considering the absolute amount per fish day or the relative amount corrected for differences in body weight). Other comparable studies carried out with rainbow trout similarly observed no decreased intake due to the higher dietary lipid content (Geurden et al, 2006;Saravanan et al, 2012;Figueiredo-Silva et al, 2012a,b), whereas trout fed with a fish-oil-enriched diet for 15 weeks displayed a significant decrease in food intake (Gélineau et al, 2001). The different response may relate to the difference in feeding duration (4 weeks in the present study) or to the fatty acid amount and composition of the lipids used for preparing the high-fat diet (a mixture of fish oil and rapeseed oil in this study), which together with the amount of lipids ingested, result in fish fed the high-fat diet having an increased intake of several fatty acids, especially myristeate, palmitate, pamitoleate, oleate, linoleate, α-linolenate, eicosapentanoate and docosahexanoate.…”

Voluntary Feed Intake in Rainbow Trout Is Regulated by Diet-Induced Differences in Oxygen Use

“…However, several other fish studies did not show an equal protein deposition with satiation feeding (e.g., 7,11). The dietinduced difference in the voluntary intake levels observed in various fish species (7,9,(15)(16)(17) might be related to the type and level of dietary nonprotein digestible energy (NPDE) source (starch vs. fat) as suggested in mammals [for review, see (18). The mechanism by which the NPDE source affects voluntary feed intake in fish has been, so far, little explored.…”

“…It has often been suggested that fish, like other animals, adjust their voluntary feed intake according to the digestible energy content of the diet in order to meet a predefined energy requirement (2)(3)(4). However, recent findings in rainbow trout (5)(6)(7)(8)(9)(10) and other teleosts (6,11,12) contradict the notion that feed intake is adjusted to have a constant digestible energy intake (DEI) 6 . Similarly, the demand for a target lean growth or protein deposition rather than for a predefined energy requirement has been proposed to regulate feed intake in fish (8,10,13,14).…”

“…Similarly, the demand for a target lean growth or protein deposition rather than for a predefined energy requirement has been proposed to regulate feed intake in fish (8,10,13,14). However, several other fish studies did not show an equal protein deposition with satiation feeding (e.g., 7,11). The dietinduced difference in the voluntary intake levels observed in various fish species (7,9,(15)(16)(17) might be related to the type and level of dietary nonprotein digestible energy (NPDE) source (starch vs. fat) as suggested in mammals [for review, see (18).…”

“…In terrestrial animals, dietary starch and fat exert their effects on feed intake via feedback mechanisms mediated by circulating glucose (19) (glucostatic regulation) and body fat store (20) (lipostatic regulation), respectively. These chemostatic control mechanisms of feed intake show inconsistent outcomes in fish (7,11). Alternatively, the thermostatic regulation of feed intake in homeotherms proposes the intake to be controlled by the animalÕs need for body heat and its ability to dissipate the extra heat to the environment generated as a by-product of food processing (21,22).…”