In the highly eutrophic lake, Frederiksborg Slotsso, the diet composition of the bream (Abramis brama L .) and roach (Rutilus rutilus L.) populations was examined during three periods with different food availability . The length range of bream and roach was 9-34 cm (TL) and 5-18 cm (TL), respectively . The relative food composition was examined for 2 cm and 1 cm length intervals of bream and roach, respectively. During all three periods, bream shifted from benthic cladocerans (Alona sp.) to zooplankton and chironomids within a transitional length of 15 .0-20 .0 cm . These foodshifts were coupled with a change in feeding behaviour from particulate to filter feeding . The biomass of chironomids was too low to sustain the consumption of larger bream (>20 .0 cm) which initiated feeding in the pelagic zone even in periods when the mean length and biomass of the preferred zooplankton, Daphnia cucullata, were low . In contrast to bream, roach fed mainly on zooplankton . With increasing size, roach progressively shifted to larger zooplankton species due to the increasing mesh size of their branchial system . The importance of benthic animals in the diet of roach was minor due to low feeding efficiency on prey buried in the sediment . Detritus appeared in the diet of bream and roach in periods of low availability of animal food items . Feeding on detritus may provide an energetic advantage to bream and roach and increase the carrying capacity for these species in lakes, where detritus is highly abundant . Especially for the larger fish due to the decrease in their relative metabolic demands . However, the ability of bream to filter feed and with increasing size to retain food items smaller than those retained by roach may be the main mechanism for the dominance of bream over roach in highly eutrophic lakes .
Background Intake of total fat is linked to obesity and inversely associated with bone density in humans. Epidemiologic and animal studies show that long-chain n–3 (ω-3) PUFAs supplied as fish oil (FO) are beneficial to skeletal health. Objective This study tested the hypothesis that increasing dietary FO would decrease adiposity and improve bone-related outcomes in growing obese mice. Methods Male C57BL/6 mice at 6 wk old were assigned to 6 treatment groups and fed either a normal-fat diet (3.85 kcal/g and 10% energy as fat) or a high-fat diet (HF; 4.73 kcal/g and 45% energy as fat) containing either 0%, 3%, or 9% energy as FO (0FO, 3FO, and 9FO, respectively) ad libitum for 6 mo. Bone structure, body composition, and serum bone-related cytokines were measured. Results The HF diet increased the expression of the adipose tissue tumor necrosis factor α (Tnfa) and serum concentrations of leptin and tartrate-resistant acid phosphatase (TRAP), and decreased serum concentrations of osteocalcin and bone-specific alkaline phosphatase (P < 0.05). FO decreased fat mass (P < 0.05), serum TRAP (P < 0.05), and adipose tissue Tnfa expression (P < 0.01). Bone content of long-chain n–3 PUFAs was increased and n–6 PUFAs were decreased with the elevation in dietary FO content (P < 0.01). Compared with mice fed 9FO, animals fed 3FO had higher femoral bone volume/total volume (25%), trabecular number (23%), connectivity density (82%), and bone mass of second lumbar vertebrae (12%) and lower femoral trabecular separation (−19%). Mice fed the 3FO HF diet had 42% higher bone mass than those fed the 0FO HF diet. Conclusions These data indicate increasing dietary FO ≤3% energy can decrease adiposity and mitigate HF diet–induced bone deterioration in growing C57BL/6 mice possibly by reducing inflammation and bone resorption. FO at 9% diet energy had no further beneficial effects on bone of obese mice.
Trialcylglycerol (TG) lipase was isolated and partially purified from rainbow trout liver. Triacylglycerol lipase activity was assayed by measuring(14)C-oleic acid release from(14)C-triolein.(14)C-oleic acid release was linear for up to two hours. Optimal activity occurred at pH 7.0 and 15°C. Most of the lipase activity was recovered in the cytosolic fraction. A 27,000-fold purification was achieved after Sepharose (Bio-gel A 0.5 M, 200-400 mesh) chromatography of a resuspended 20% ammonium sulfate fraction. The molecular weight of the trout hepatic lipase as determined by size-exclusion chromatography and by SDS-polyacrylamide gel electrophoresis was 40-43 kD. Lipase-mediated hydrolysis of TG resulted in the production of diacylglycerols, monoacylglycerols, and fatty acids. Kinetic analysis indicated that Vmax=0.016 nmol/h/mg protein and that Km=0.28 mM triolein. Lipolytic activity was enhanced in the presence of cAMP/ATP-Mg(2+). These results suggest that the liver of trout possesses a neutral TG lipase that is responsible for mobilizing stored TG and is catalytically activated by phosphorylation.
Background Linoleic acid (LA; 18:2n–6) has been considered to promote low-grade chronic inflammation and adiposity. Studies show adiposity and inflammation are inversely associated with bone mass. Objectives This study tested the hypothesis that decreasing the dietary ratio of LA to α-linolenic acid (ALA, 18:3n–3), while keeping ALA constant, mitigates high-fat diet (HF)-induced adiposity and bone loss. Methods Male C57BL/6 mice at 6 wk old were assigned to 4 treatment groups and fed 1 of the following diets ad libitum for 6 mo: a normal-fat diet (NF; 3.85 kcal/g and 10% energy as fat) with the ratio of the PUFAs LA to ALA at 6; or HFs (4.73 kcal/g and 45% energy as fat) with the ratio of LA to ALA at 10:1, 7:1, or 4:1, respectively. ALA content in the diets was kept the same for all groups at 1% energy. Bone structure, body composition, bone-related cytokines in serum, and gene expression in bone were measured. Data were analyzed using 1-factor ANOVA. Results Compared with those fed the NF, mice fed the HFs had 19.6% higher fat mass (P < 0.01) and 13.5% higher concentration of serum tartrate-resistant acid phosphatase (TRAP) (P < 0.05), a bone resorption cytokine. Mice fed the HFs had 19.5% and 12.2% lower tibial and second lumbar vertebral bone mass, respectively (P < 0.01). Decreasing the dietary ratio of LA to ALA from 10 to 4 did not affect body mass, fat mass, serum TRAP and TNF-α, or any bone structural parameters. Conclusions These data indicate that decreasing the dietary ratio of LA to ALA from 10 to 4 by simply reducing LA intake does not prevent adiposity or improve bone structure in obese mice.
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