Relation between water temperature (T, °C) and heat production in rainbow trout fed to satiation.

<p>The heat production values (H, kJ kg^−0.8 d⁻¹) are calculated for rainbow trout fed to satiation from literature data <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034743#pone.0034743-Azevedo1" target="_blank">[57]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034743#pone.0034743-Glencross1" target="_blank">[58]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034743#pone.0034743-Glencross2" target="_blank">[59]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034743#pone.0034743-Glencross3" target="_blank">[60]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034743#pone.0034743-Kim1" target="_blank">[61]</a> and from the present study. H was curvilinearly related to temperature, H = 26.6×e^0.0923×T, R² = 0.73.</p

Effect of diet composition on post-prandial plasma glucose and triglycerides in rainbow trout.

<p>Seven hours post-prandial plasma levels (least squares mean ± SD) of glucose and triglycerides (TAG) of rainbow trout fed diets having contrast in P/E ratio and NPE source. Glucose was affected by dietary P/E ratio, NPE source and their interaction (P<0.001). In contrast, TAG levels were affected only by the NPE source (P = 0.003) and not by P/E ratio and their interaction effect (P>0.05).</p

Conceptual illustration of the hypothesis tested in the present study.

<p>It is hypothesized that under non-limiting water oxygen level (normoxia) food intake of fish fed a diet deficient in essential amino acids is compromised by a physiological constraint in oxygen consumption. To test the hypothesis, fish were fed under normoxia with diets contrasting in essential amino acids (lysine and methionine) composition: an imbalanced (ImbAA) <i>vs.</i> a balanced amino acid (BAA) diet. The difference in amino acid composition of the diet is expected to create differences in metabolism, which will alter the amount of oxygen consumption per unit of food intake. This amount of oxygen consumption per unit of food is higher at the ImbAA diet than at the BAA diet (as indicated by the differences in the slope of lines). As such: 1) If oxygen consumption is constraining the food intake, then the food intake between ImbAA and BAA fed fish will be different but the oxygen consumption will be similar; 2) If oxygen consumption is not constraining the food intake, then food intake between ImbAA and BAA fed fish will be different but also the oxygen consumption. Further, to verify the effect of dietary amino acid induced changes in oxygen consumption on food intake, we measured food intake under limiting water oxygen level (hypoxia) as a positive control.</p

Nitrogen, fat and energy balance in rainbow trout fed the experimental diets for 6 weeks¹.

<p>SEM, Standard error mean; GNI, Gross nitrogen intake; FN, Faecal nitrogen loss; DNI, Digestible nitrogen intake; BUN, Branchial and urinary nitrogen loss; RN, Retained nitrogen; GFI, Gross fat intake; FF, Faecal fat loss; DFI, Digestible fat intake; RF, retained fat; RF/DF, fat efficiency; GEI, Gross energy intake; FE, faecal energy loss; DEI, digestible energy intake; BUE, branchial and urinary energy loss; MEI, metabolisable energy intake; RE, retained energy.</p>1<p>Values represent least squares (LS) means (n = 3), row means with different superscript letters were significantly different and assigned only if interaction effect was significant (P<0·05).</p>2<p>H_P/EF - High P/E ratio diet with fat as main non-protein energy source; H_P/EC - High P/E ratio diet with carbohydrate as main non-protein energy source; L_P/EF - Low P/E ratio diet with fat as main non-protein energy source; L_P/EC - Low P/E ratio diet with carbohydrate as main non-protein energy source.</p

Voluntary feed intake and growth performance of rainbow trout fed the experimental diets for 6 weeks¹.

<p>DM, dry matter; FI_PCT, Feed intake per percentage body weight; FI_ABS, Absolute feed intake; FI_MBW, Feed intake per metabolic body weight; DGC, Daily growth coefficient; FGR, Feed gain ratio.</p>1<p>Values represent least squares (LS) means (n = 3), row means with different superscript letters were significantly different and assigned only if interaction effect was significant (P<0.05).</p>2<p>H_P/EF - High P/E ratio diet with fat as main non-protein energy source; H_P/EC - High P/E ratio diet with carbohydrate as main non-protein energy source; L_P/EF - Low P/E ratio diet with fat as main non-protein energy source; L_P/EC - Low P/E ratio diet with carbohydrate as main non-protein energy source.</p

Fish performance, metabolic parameters and body composition of rainbow trout fed to satiation with balanced amino acid diet and imbalanced amino acid diet at two levels of water dissolved oxygen: hypoxia <i>vs.</i> normoxia for 42 days.

<p>SEM, Standard error mean; DO, dissolved oxygen; DM, dry matter; DPI, digestible protein intake.</p><p>Mean values in a row with unlike superscript were significantly different and assigned only if the interaction effect was significant (<i>p</i><0.05).</p>*<p>Protein retention efficiency (%)  =  (Wet protein gain/protein intake in dry weight) ×100.</p>**<p>Initial body composition (g kg wet weight⁻¹): 157, protein and 80.5, fat.</p

Analysed nutrient and amino acid composition of the amino acid imbalanced and balanced diets.

*<p>Digestible energy determined under normoxia treatment of the present study <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0072757#pone.0072757-Saravanan1" target="_blank">[31]</a></p>†<p>For rainbow trout the estimated requirement for lysine, vary from 4.5 to 6.3% crude protein <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0072757#pone.0072757-NRC1" target="_blank">[32]</a> and for methionine, it varies from 1.8 to 2.14% crude protein depending on level of cysteine <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0072757#pone.0072757-Kim1" target="_blank">[13]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0072757#pone.0072757-NRC1" target="_blank">[32]</a>.</p

Food intake and oxygen consumption of trout in relation to the proposed hypothesis (figure 1).

<p>The measured food intake and oxygen consumption of rainbow trout fed to satiation with a balanced amino acid diet and an imbalanced amino acid diet at two levels of water dissolved oxygen: hypoxia <i>vs.</i> normoxia. Values are mean±SD (<i>n</i> = 3).</p

Effect of diet composition on digestible energy intake (DEI) in rainbow trout.

<p>Fish were fed to satiation with iso-energetic diets of different macronutrient composition having contrast in P/E ratio (high, H_P/E vs. low, L_P/E) and NPE source (fat, F vs. carbohydrates, C) for 6 weeks. The bars show the amount of DEI derived from the digestible protein, fat and total carbohydrate (nitrogen-free extract) for each dietary group. Different superscripts indicate significant differences in total DEI.</p

Effect of diet and dissolved oxygen on food intake and oxygen consumption in rainbow trout.

<p>Rainbow trout fed to satiation with a balanced amino acid diet and an imbalanced amino acid diet at two levels of water dissolved oxygen (DO): hypoxia <i>vs.</i> normoxia. (a) Food intake was affected by dietary amino acid composition (<i>p</i><0.001), water DO level (<i>p</i><0.001), and the interaction between both factors (<i>p</i> = 0.02). (b) Oxygen consumption was affected by water DO level (<i>p</i><0.001) but unaffected by dietary amino acid composition (<i>p</i> = 0.36) and the interaction between both factors (<i>p</i> = 0.31). Values are mean±SD (<i>n</i> = 3, group of 30 fish tank^-1).</p