Dynamics of mitochondrial adaptation and energy metabolism in rainbow trout (Oncorhynchus mykiss) in response to sustainable diet and temperature.

Impacts of plant-based ingredients and temperatures on energy metabolism in rainbow trout was investigated. A total of 288 fish (mean body weight: 45.6 g) were fed four isocaloric, isolipidic, and isonitrogenous diets containing 40% protein and 20% lipid and formulated as 100% animal-based protein (AP) and a blend of 50% fish oil (FO) and 50% camelina oil (CO); 100% AP and100% CO; 100% plant-based protein (PP) and a blend of 50% FO and 50% CO or 100% PP and 100% CO at 14 or 18 °C for 150 d. Diet did not significantly affect weight gain (WG) (P = 0.1902), condition factor (CF) (P = 0.0833) or specific growth rate (SGR) (P = 0.1511), but diet significantly impacted both feed efficiency (FE) (P = 0.0076) and feed intake (FI) (P = 0.0076). Temperature did not significantly affect WG (P = 0.1231), FE (P = 0.0634), FI (P = 0.0879), CF (P = 0.8277), or SGR (P = 0.1232). The diet × temperature interaction did not significantly affect WG (P = 0.7203), FE (P = 0.4799), FI (P = 0.2783), CF (P = 0.5071), or SGR (P = 0.7429). Furthermore, temperature did not influence protein efficiency ratio (P = 0.0633), lipid efficiency ratio (P = 0.0630), protein productive value (P = 0.0756), energy productive value (P = 0.1048), and lipid productive value (P = 0.1386); however, diet had significant main effects on PER (P = 0.0076), LPV (P = 0.0075), and PPV (P = 0.0138). Temperature regimens induced increased activities of mitochondrial complexes I (P = 0.0120), II (P = 0.0008), III (P = 0.0010), IV (P < 0.0001), V (P < 0.0001), and citrate synthase (CS) (P < 0.0001) in the intestine; complexes I (P < 0.0001), II (P < 0.0001), and CS (P = 0.0122) in the muscle; and complexes I (P < 0.0001), II (P < 0.0001), and III (P < 0.0001) in the liver. Similarly, dietary composition significantly affected complexes I (P < 0.0001), II (P < 0.0001), IV (P < 0.0001), V (P < 0.0001), and CS (P < 0.0001) in the intestine; complexes I (P < 0.0001), II (P < 0.0001), III (P = 0.0002), IV (P < 0.0001), V (P = 0.0060), and CS (P < 0.0001) in the muscle; and complexes I (P < 0.0001), II (P < 0.0001), IV (P < 0.0001), V (P < 0.0001), and CS (P < 0.0001) in the liver activities except complex III activities in intestine (P = 0.0817) and liver (P = 0.4662). The diet × temperature interaction impacted CS activity in the intestine (P = 0.0010), complex II in the muscle (P = 0.0079), and complexes I (P = 0.0009) and II (P = 0.0348) in the liver. Overall, comparing partial to full dietary substitution of FO with CO, partial dietary replacement showed similar effects on complex activities.

Diets are one of the most important consideration in aquaculture production as more than 50% of production costs are incurred in raising cultured fish to market size. As the price of FM and FO continues to increase, it is necessary to seek alternative sources of proteins and oils for sustainable aquaculture development. Plant-based ingredient sources have appeared as sustainable alternatives; however, it is uncertain whether the uses of plant-based alternatives will be appropriate in securing the production of carnivorous aquaculture species in the context of global warming, with studies postulating on the potential effects of climate change on fish growth and health. A study was conducted to examine how the replacement of FM and FO with sustainable plant-based protein and camelina oil (CO) as ingredient sources at 14 or 18 °C would affect the growth performance, nutrient utilization efficiencies, and mitochondrial enzyme activity in rainbow trout. Based on the results, mitochondrial enzyme activities were generally higher at 18 °C and CO could replace 50% dietary FO without negative effects on rainbow trout. Overall, our study demonstrated that animal-based protein with CO is as good as animal-based with FO for growth and health, thus providing potentially sustainable diet options for aquaculture.

Interactive effects of dietary lipid and phenotypic feed efficiency on the expression of nuclear and mitochondrial genes involved in the mitochondrial electron transport chain in rainbow trout.

A 2 × 3 factorial study was conducted to evaluate the effects of dietary lipid level on the expression of mitochondrial and nuclear genes involved in electron transport chain in all-female rainbow trout Oncorhynchus mykiss. Three practical diets with a fixed crude protein content of 40%, formulated to contain 10% (40/10), 20% (40/20) and 30% (40/30) dietary lipid, were fed to apparent satiety to triplicate groups of either low-feed efficient (F120; 217.66 ± 2.24 g initial average mass) or high-feed efficient (F136; 205.47 ± 1.27 g) full-sib families of fish, twice per day, for 90 days. At the end of the experiment, the results showed that there is an interactive effect of the dietary lipid levels and the phenotypic feed efficiency (growth rate and feed efficiency) on the expression of the mitochondrial genes nd1 (NADH dehydrogenase subunit 1), cytb (Cytochrome b), cox1 (Cytochrome c oxidase subunits 1), cox2 (Cytochrome c oxidase subunits 2) and atp6 (ATP synthase subunit 6) and nuclear genes ucp2α (uncoupling proteins 2 alpha), ucp2ß (uncoupling proteins 2 beta), pparα (peroxisome proliferator-activated receptor alpha), pparß (peroxisome proliferatoractivated receptor beta) and ppargc1α (proliferator-activated receptor gamma coactivator 1 alpha) in fish liver, intestine and muscle, except on ppargc1α in the muscle which was affected by the diet and the family separately. Also, the results revealed that the expression of mitochondrial genes is associated with that of nuclear genes involved in electron transport chain in fish liver, intestine and muscle. Furthermore, this work showed that the expression of mitochondrial genes parallels with the expression of genes encoding uncoupling proteins (UCP) in the liver and the intestine of rainbow trout. This study for the first time presents the molecular basis of the effects of dietary lipid level on mitochondrial and nuclear genes involved in mitochondrial electron transport chain in fish.

Chemical contaminants in fish feeds used in federal salmonid hatcheries in the USA.

Recent studies have demonstrated that fish feeds contain significant concentrations of contaminants, many of which can bioaccumulate and bioconcentrate in fish. Organochlorine (OC) contaminants are present in the fish oils and fish meals used in feed manufacture, and some researchers speculate that all fish feeds contain measurable levels of some contaminants. To determine the concentration of contaminants in feeds used in US Fish and Wildlife Service's National Fish Hatcheries, we systematically collected samples of feed from 11 cold-water fish hatcheries. All samples (collected from October 2001 to October 2003) contained at least one polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated dibenzofuran (PCDF), polychlorinated biphenyl (PCB) congener, or dichlorodiphenyltrichloroethane (DDT) metabolite. Of the 55 samples in which they were analyzed 39 contained PCDDs, 24 contained PCDFs and 24 contained DDT or its metabolites. There were 10- to 150-fold differences in concentrations of total PCBs, PCDDs, PCDFs and DDT. Although PCBs were the most commonly detected contaminant in our study, concentrations (range: 0.07-10.46 ng g(-1) wet weight) were low compared to those reported previously. In general, we also found lower levels of OCs than reported previously in fish feed. Perhaps most notable was the near absence of OC pesticides - except for DDT or its metabolites, and two samples containing hexachlorocyclohexane (HCH). While contaminant concentrations were generally low, the ecological impacts can not be determined without a measure of the bioaccumulation of these compounds in the fish and the fate of these compounds after the fish are released.