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First published online November 24, 2003
Journal of Experimental Biology 207, 75-86 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00712

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Physiological modulation of iron metabolism in rainbow trout (Oncorhynchus mykiss) fed low and high iron diets

P. Carriquiriborde¹, R. D. Handy^2,* and S. J. Davies²

¹ Environmental Research Centre, National University of La Plata-CONICET, La Plata, Bs. As., Argentina
² School of Biological Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK

View larger version (21K): [in a new window]   Fig. 1. Effect of casein-based diet containing low (filled square), normal (filled diamond) and high (filled circle) levels of dietary Fe for 8 weeks (measured Fe in diet, 33, 175 and 1975 mg kg-1, respectively) on tissue Fe concentration in the intestine (A), stomach (B), liver (C), serum (D), muscle (E) and gill (F) of rainbow trout. Values are means ± S.E.M. (N=9 fish per time point). Different letters (a, b or c) denote statistically significant differences in tissue Fe concentration within each time point between experimental dietary Fe treatments (ANOVA followed by LSD test, P<0.05). All data are denoted the letter a (not shown for clarity in figures) unless otherwise indicated. Thus, b indicates the high-Fe diet is different from either low or normal diets in the panels for Fig. 1, but low and normal diets are not different from each other. No treatment differences were observed in muscle or gill. Asterisk indicates a significant difference between initial values (open symbol) in stock fish fed normal commercial trout food compared with fish at week 2 on the normal Fe diet (Student's t-test, P<0.05, N=9).

View larger version (12K): [in a new window]   Fig. 2. (A) Total iron binding capacity (TIBC), (B) unsaturated iron binding capacity (UIBC) and (C) the percentage of transferrin in the serum saturated with Fe in rainbow trout fed casein-based diets containing low (filled square), normal (filled diamond) and high (filled circle) levels of Fe for 8 weeks. Values are means ± S.E.M. (N=6). Other details and statistics as in Fig. 1.

View larger version (12K): [in a new window]   Fig. 3. NADH-dependent ferrireductase activity in gill (A), intestine (B) and liver (C) of rainbow trout fed a casein-based diet containing low (filled square), normal (filled diamond) and high (filled circle) levels of Fe for 8 weeks. Values are means ± S.E.M. (N=6). Other details and statistics as in Fig. 1. No differences were observed between treatments in gill tissue. No differences were observed between initial fish and those on the normal Fe diet at week 2. Insets are log[Fe] in tissue correlated with ferrireductase activity for intestine (B inset, y=-16.63x+38.10 for low- and high-Fe diets, N=18) and liver (C inset, y=105.03x-1.24, for normal and high-Fe diets, N=18). Note, ferrireductase activity is normalised per minute (nmol mg-1 min-1).

View larger version (10K): [in a new window]   Fig. 4. Correlation between percentage Fe saturation of transferrin in the serum and log[Fe] in the liver (A), and liver ferrireductase activity (B) in rainbow trout fed a caseinbased diet containing normal (filled diamond) and high (filled circle) levels of iron. The equation for the linear fits are y=0.02x+0.01 and y=2.55x-18.56 for A and B, respectively (N=18). Note, ferrireductase normalised activity is per minute (nmol mg-1 min-1).

View larger version (12K): [in a new window]   Fig. 5. Thiobarbituric acid reactive substances (TBARS) in gill (A), intestine (B) and liver (C) of rainbow trout fed a casein-based diet containing low (filled square), normal (filled diamond) and high (filled circle) levels of iron. Values are means ± S.E.M. (N=6). Other details and statistics as in Fig. 1. No statistical differences were observed between TBARS of initial fish and those on the normal-Fe diet at week 2. Insets are log[Fe] in tissue correlated with TBARS for intestine (B inset, y=0.33x+0.55, for all diets N=27) and liver (panel C insert, y=8.79x+1.72, for normal and high-Fe diets, N=18).

View larger version (98K): [in a new window]   Fig. 6. Sections of liver (7 µm) stained with Mallory's trichrome from fish fed (A) low (B) normal- and (C) high-Fe diets for 8 weeks. Livers are healthy, but show some subtle changes in intracellular glycogen storage and sinusoid space between treatments. Fish fed on the low-Fe diet showed smaller hepatocytes, with less glycogen storage (arrows), and slightly more sinusoid space (S) than normal diet controls. Livers from fish fed the high-Fe diet had slightly more sinusoid space than controls, and had slightly larger (mild hypertrophy) hepatocytes that contained less glycogen than controls. Scale bars, 40 µm.