The impact of nutritional status and diet composition on mitochondrial oxidative phosphorylation (OXPHOS) in fish remains largely unknown. To identify biomarkers of interest in nutritional studies, herein we obtained a deep-coverage transcriptome by 454 pyrosequencing of liver and skeletal muscle cDNA normalised libraries from long-term starved gilthead sea bream (Sparus aurata) and fish fed different diets. After clean-up of high-throughput deep sequencing reads, 699,991 and 555,031 high-quality reads allowed de novo assembly of liver and skeletal muscle sequences, respectively (average length: 374 and 441 bp; total megabases: 262 and 245 Mbp). An additional incremental assembly was completed by integrating data from both tissues (hybrid assembly). Assembly of hybrid, liver and skeletal muscle transcriptomes yielded, respectively, 19,530, 11,545 and 10,599 isotigs (average length: 1330, 1208 and 1390 bp, respectively) that were grouped into 15,954, 10,033 and 9189 isogroups. Following annotation, hybrid transcriptomic data were used to construct an oligonucleotide microarray to analyse nutritional regulation of the expression of 129 genes involved in OXPHOS in S. aurata. Starvation upregulated cytochrome c oxidase components and other key OXPHOS genes in the liver, which exhibited higher sensitive to food deprivation than the skeletal muscle. However, diet composition affected OXPHOS in the skeletal muscle to a greater extent than in the liver: most of genes upregulated under starvation presented higher expression among fish fed a high carbohydrate/low protein diet. Our findings indicate that the expression of coenzyme Q-binding protein (COQ10), cytochrome c oxidase subunit 6A2 (COX6A2) and ADP/ATP translocase 3 (SLC25A6) in the liver, and cytochrome c oxidase subunit 5B isoform 1 (COX5B1) in the liver and the skeletal muscle, are sensitive markers of the nutritional condition that may be relevant to assess the effect of changes in the feeding regime and diet composition on fish farming.

The replacement of fishmeal with plant-based proteins in aquafeeds is key for sustainable aquaculture but may compromise filet pigmentation in rainbow trout (Oncorhynchus mykiss), a quality trait dependent on astaxanthin (Ax) deposition and metabolism. This study aimed to assess the effects of graded fishmeal replacement with a plant protein blend on Ax retention, pigmentation, lipid metabolism, and gut microbiota composition. Rainbow trout were fed three isoenergetic diets containing 60%, 36%, or 12% fishmeal, each supplemented with equal amounts of natural Ax from Haematococcus pluvialis, for 12 weeks. Ax retention, pigmentation, plasma metabolites, lipid digestibility, and distal intestinal microbiota were evaluated. The high plant protein diet (12% fishmeal) significantly reduced Ax concentrations in filet and plasma and decreased dorsal and belly pigmentation scores (p < 0.05). It also lowered plasma cholesterol and bile acid levels by 18–30%, reduced di-esterified Ax digestibility by 15%, and lipid absorption efficiency by 12%. The gut microbiota shifted significantly, with a marked reduction in Bacillaceae, positively correlated with Ax retention and pigmentation. Fish fed High Plant Meal diets exhibited impaired performance parameters, along with reduced lipid accumulation in the liver. High plant meal compromises Ax bioavailability by altering cholesterol–bile acid metabolism and gut microbiota, impairing Ax absorption. However, moderate inclusion of plant meal preserved pigmentation, underscoring the need for dietary cholesterol management and microbiota modulation in plant-based aquafeeds.

This study examines the synthesis and characterization of the Prussian Blue analogue Manganese Hexacyanochromate (MnHCCr) on glassy carbon electrodes. Immobilization was achieved via electrochemical deposition from a stable colloidal suspension using cyclic voltammetry or chronoamperometry. Characterization through SEM, AFM, and XRD confirmed the formation of homogeneous coatings with a cubic crystal structure. Electrochemical analysis revealed four distinct redox processes associated with the Mn ²⁺ /Mn ³⁺ and Cr ³⁺ /Cr ²⁺ metal centers. The linear relationship between peak current (i _p ) and the square root of the scan rate (v ^1/2 ) indicates a diffusion-controlled process, allowing for the determination of the diffusion coefficient (D ₀ ) for electrolyte alkali ions. Furthermore, electron transfer kinetics (k°) demonstrated that smaller ionic radii (e.g., Li ⁺ ) result in faster transfer rates (Li ⁺ > Na ⁺ > K ⁺ > NH ₄ ⁺ ) due to lower energy rearrangement and favorable solvent interactions. These results validate this deposition method as a robust technique for creating functionalized surfaces, offering significant potential for applications in electrocatalysis and the development of high-precision chemical sensors.