Fish White Muscle Research Articles

Unraveling effective modified atmosphere conditions to improve the quality of refrigerated stored dark and white muscle fish

Although MAP in fish under refrigerated storage has been investigated since 1980, there is a knowledge gap about ideal concentration gases to improve the quality of dark- or medium/high-fat muscle fish (DM) and white- or lean/low-fat muscle fish (WM). As it is essential to industrial application, this study aimed to find promising MAP conditions to maximize fresh WM and DM quality throughout refrigerated storage based on bacteriological shelf life, physicochemical, and sensory parameters. Research articles were retrieved from Science Direct, PubMed, Web of Science, and Scopus without establishing a research period (n = 3840), and 148 were included in this systematic and meta-analytic review. Identifying an effective MAP treatment was impossible for WM, considering all physicochemical parameters evaluated in this study. However, promising MAP ranges for further optimization were found for WM (60–75% CO2/25–40% N2 and 40–80% CO2/10–30% N2/10–30% O2), which increased shelf life by 2–12 days, reduced lipid oxidation (LOX) by 1.50–3.00 mg malonaldehyde (MDA)/kg, maintained color (∆E difference < 1), and sensory quality. For DM, the best treatment was 60% CO2/40% N2 since it increased bacteriological and sensory shelf life by 10–11 days, reduced LOX by 2 mg MDA/kg and biogenic amines by 6.50–172.60 mg/kg, and retained color and hardness quality close to fresh fish. Nevertheless, studies should evaluate gas mixtures from 40 to 100% CO2 to 0–60% N2 (without O2) to optimize our findings further. Therefore, MAP is a fresh-keeping preservation alternative to meet the current trend for sustainable development of the fish production chain.

Effects of exercise training on the external morphology, growth performance, swimming ability, body composition and metabolism of juvenile black seabream Acanthopagrus schlegelii

Multiple studies have shown that exposure to moderate water currents (exercise training) can improve growth and physiological performance of hatchery-reared fish. Proactive implementation of sustained aerobic swimming training can be particularly beneficial for improving post-release performance of fish in stock enhancement- or ‘ranching’ programs. Black seabream Acanthopagrus schlegelii is an important species in aquaculture and stock enhancement in the East China Sea. For juveniles of this species, we assess the impacts of exercise training at various flow rates on the morphology, growth performance, swimming ability, body composition and locomotors metabolism. A group of sibling juvenile fish (initial mass: 13.72 ± 0.29 g) underwent daily exercise training for 12 h (9:00–21:00) over 30 days at four different water velocities (0, 1, 2, or 4 body lengths per second, BL/s). All the trained fish exhibited a significant decrease in their respiratory metabolic rate during the test of swimming ability. Fish from the 2 BL/s training group exhibited a significantly increased burst swimming speed compared to the other groups. Fish from 1 BL/s training group showed elevated hexokinase activities in the white muscle and citrate synthase activities in the liver compared to the 0 BL/s group. Citrate synthase activities in the white muscle of fish from the 2 BL/s training group were elevated, along with citrate synthase activities in the liver, as compared to 0 BL/s. The fish in the 4 BL/s training group showed a tendency for increased crude protein content and a corresponding decrease in crude lipid content. Morphological analysis revealed that fish in the 4 BL/s group exhibited larger dorsal fins and more streamlined body profiles, compared to 0 BL/s. Activities of white muscle citrate synthase as well as liver hexokinase activity were higher in the 4 BL/s group, while lactate content activity in the white muscle were lower compared to 0 BL/s. These findings underscore the effectiveness of training at 2 BL/s, offering a promising strategy to enhance the performance of juvenile black seabream for stocking initiatives.

Exploring high hydrostatic pressure for enhancing the preservation of white and dark muscle fish fillets stored at different packaging systems under refrigeration

Exploring high hydrostatic pressure for enhancing the preservation of white and dark muscle fish fillets stored at different packaging systems under refrigeration

Hexachlorobenzene and omega-3 fatty acid intake from traditional foods in the northern Yukon: A risk and benefit analysis

A human biomonitoring study was conducted in the community of Old Crow, Yukon, in 2019, finding that levels of hexachlorobenzene (HCB) in plasma were elevated in the community relative to the general Canadian population. The aim of this study was to estimate dietary intake of both hexachlorobenzene, and the nutrient omega-3 fatty acids from locally harvested traditional foods in Old Crow, with the aim of identifying possible regional sources of exposure. A stochastic model was constructed to estimate intake of both hexachlorobenzene and the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Average predicted hexachlorobenzene exposure levels from traditional food consumption in Old Crow were below the tolerable daily intake of 1600–1700 ng/kg body weight/day in both average (18 ng/kg body weight/day) and short-term maximum (27 ng/kg body weight/day) exposure models. The primary contributors to average hexachlorobenzene intake were caribou fat, bone marrow, ribs, and kidneys, and Chinook salmon muscle. Average estimated dietary EPA + DHA intake levels from traditional foods were below the recommendation of 2.1 to 3.2 g of EPA + DHA per week in the average (1.6 g/week) exposure model, but above this recommendation in the short-term maximum model (3.3 g/week). The primary contributors to average EPA + DHA intake were the meat of Chinook, coho, and, chum salmon muscle, and whitefish muscle and eggs. The results of this study support the message that traditional foods continue to be an important source of nutrients and other health benefits and that the health benefits of traditional foods generally outweigh contaminant risks.

Effect of cooking temperature on metal concentrations and speciation in fish muscle and seal liver

Fish and marine mammals constitute a significant part of the country food diet of many Indigenous communities in Canada. These animals sometimes accumulate essential elements as well as elevated levels of toxic metals. We experimentally assessed how changes in cooking temperature (23–99 °C by boiling) modified elemental concentrations in whitefish muscle and grey seal liver (two organs commonly consumed in some northern communities). Wet and dry elemental concentrations changed linearly as a function of temperature, and two patterns were observed: methylmercury, selenium, and rare earth elements tended to remain associated with the food during cooking, whereas alkali, alkaline-earth metals, and arsenic were significantly transferred to cooking juices. Mass balances indicated that speciation of mercury was stable during cooking. Because elements generally behaved similarly as those of their periodic table group or their ecotoxicological classes (A, B, intermediate), we propose that elemental behavior during cooking is partly a function of chemical affinity, and this relationship can be used to predict the behavior of data-poor elements of emerging concern, such as technology-critical elements. Furthermore, the marked increases and decreases in elemental concentrations during cooking (e.g., −14% As and +39% Se in whitefish; −22% Cd and +55% Hg in seal liver, on a wet weight basis) should be considered when assessing risk because current exposure models usually only consider elemental concentrations in raw food.

Supplementation Effects of an Alpha-Casozepine and White Fish Muscle Hydrolyzed Complementary Feed on Canine Separation-Related Disorders and Quality of Life of Dogs and Their Pet Caregivers

Supplementation Effects of an Alpha-Casozepine and White Fish Muscle Hydrolyzed Complementary Feed on Canine Separation-Related Disorders and Quality of Life of Dogs and Their Pet Caregivers

Proteomics of Fish White Muscle and Western Blotting to Detect Putative Allergens.

A detailed workflow is provided for preparation from teleost fish white muscle of extracts for proteomics analysis. The protocol generates samples that can be analyzed by SWATH (Sequential Window data independent Acquisition of the Total High-resolution-Mass Spectra), a modern MS-based quantitative label free technology. The main steps for the extraction of three independent protein fractions, (1) soluble sarcoplasmic, (2) soluble myofibrillar, and (3) insoluble material, from fish white muscle are detailed. Coupled to the protein extraction protocol a Western blotting approach is outlined for detection of common fish allergens, in this case β-parvalbumin, in the white muscle sarcoplasmic protein fraction.

Conservation of freshwater eels in food‐web studies: Non‐lethal stable isotope analyses substitute fin for muscle tissue with lipid correction

AbstractAquatic food‐web studies involving fish and using stable isotope analysis typically sample fish white muscle, which generally requires the fish to be euthanised. Alternatively, fin tissue can be sampled non‐lethally, avoiding the need to euthanise an animal to obtain what is usually a relatively small tissue sample. We set out to develop equations for converting δ13C and δ15N values from derived non‐lethally sampled fin tissue to equivalent white muscle tissue, for use in food‐web studies. We explored δ13C and δ15N values of paired fin‐clips and white muscle from two species of anguillid fishes, the endemic longfin eel (Anguilla dieffenbachii), and the Australasian shortfin eel (A. australis), sourced from multiple studies spread throughout New Zealand. We also examined the effect of lipid extraction on δ13C and δ15N, which reduced variability of δ13C when compared to untreated samples. We were also able to estimate δ13C values of equivalent lipid‐extracted muscle samples directly from untreated fin. For δ15N, paired untreated fin and muscle values were not statistically different so fin δ15N can be used as a direct estimate of muscle δ15N. Solvent lipid extraction with a methanol–chloroform mixture, however, altered δ15N values and increased variability, so should be avoided. We present equations to estimate lipid‐corrected δ13C values of muscle tissue for use in stable isotope studies of freshwater anguillids, avoiding euthanasia. Our results demonstrate that δ13C and δ15N values can be accurately derived from non‐lethally obtained fin clips, reducing unnecessary mortality in fish species of conservation concern.

Dietary Selenium Promotes Somatic Growth of Rainbow Trout (Oncorhynchus mykiss) by Accelerating the Hypertrophic Growth of White Muscle.

As a nutritionally essential trace element, selenium (Se) is crucial for fish growth. However, the underlying mechanisms remain unclear. Fish somatic growth relies on the white muscle growth. This study aimed to explore the effects and underlying mechanisms of Se on fish white muscle growth using a juvenile rainbow trout (Oncorhynchus mykiss) model. Fish were fed a basal diet unsupplemented or supplemented with selenium yeast at nutritional dietary Se levels (2 and 4mg/kg Se, respectively) for 30days. Results showed that dietary Se supplementation significantly enhanced trout somatic growth. Histological and molecular analysis of trout white muscle tissues at the vent level showed that dietary Se supplementation elevated the total cross-sectional area of white muscle, mean diameter of white muscle fibers, protein content, nuclei number, and DNA content of individual muscle fiber, and suppressed the activities of calpain system and ubiquitin-proteasome pathway. Overall, this study demonstrated that dietary Se within the nutritional range inhibits calpain- and ubiquitin-mediated protein degradation and promotes the fusion of myoblasts into the existed muscle fibers to promote the hypertrophic growth of white muscle, thereby accelerating the somatic growth of rainbow trout. Our results provide a mechanistic insight into the regulatory role of Se in fish growth.

Assessment of the effects of atrazine, dichlorodiphenyltrichloroethane, and dimethoate on freshwater fish (Oreochromis mossambicus): a case study of the A2 farmlands in Chiredzi, in the southeastern part of Zimbabwe.

A study was carried out to assess the levels and effects of atrazine, dimethoate, and dichlorodiphenyltrichloroethane on freshwater fish (Oreochromis mossambicus). Water and fish were sampled once from a dam within the Hippo Valley A2 farmlands in Chiredzi, in the southeastern part of Zimbabwe. The samples were screened for atrazine, dimethoate, and dichlorodiphenyltrichloroethane (DDT), the pesticides commonly used in the region. Atrazine and dimethoate are pesticides commonly used in the control of weeds and pests in the agricultural production of sugarcane in Hippo Valley, Chiredzi region. The effects of the pesticides on biochemical endpoints of the sampled fish were determined. The analyzed biochemical end parameters were superoxide dismutase, catalase, glutathione S-transferase, and glutathione peroxidase activities in liver and white muscle fish extracts. Dichlorodiphenyltrichloroethane was observed in water and fish muscle tissue at concentrations of 131.3 μg/l and 171.7 μg/kg, respectively, while atrazine was detected at concentrations of 6.15 μg/l and 142.0 μg/kg in water and fish muscle tissue, respectively. The observed concentrations of atrazine and DDT in water samples were above the limits permissible by the World Health Organization in drinking water. Dimethoate was found in concentrations of 4.21 μg/l and 1.30 μg/kg in water and fish muscle tissue respectively. The observed concentration of dimethoate in water was below the acceptable limit set by the Guidelines for Canadian Drinking Water. Antioxidant enzyme activities were increased significantly (p < 0.05) in fish exposed to water from Hippo Valley, Chiredzi, when compared with the controls. The enhanced activities of the studied antioxidant enzyme system were attributed to exposure to pollutants in the water body. Alterations of the biochemical integrity of fish indicate negative effects of the pesticides on the well-being of fish and undoubtedly other aquatic biota as well.

Seasonal changes in European whitefish muscle and invertebrate prey fatty acid composition in a subarctic lake

Abstract Ambient light and temperature show extreme seasonal variation in subarctic lakes due to the midnight sun period in summer and cold polar night period in winter. These changes have clear impacts on fish feeding and reproduction cycles, potentially affecting the fatty acid (FA) composition of muscle. Despite extensive research into fish FA over recent decades, we know little about intra‐annual changes of fish FA profile and content. We studied intra‐annual changes in the FA profile (mol%) and content (mg g‐1 dry weight) of sexually mature European whitefish (Coregonus lavaretus) muscle in a large and deep subarctic lake located in northern Fennoscandia. We collected fish, zooplankton, and benthic macroinvertebrate samples during 3 ice‐covered months, including December (during whitefish spawning), and 3 open‐water months. Fish size, age, sex, stomach content and fullness, and gonadosomatic index were also assessed as co‐variates. Whitefish changed diet from benthic macroinvertebrates in winter to zooplankton in summer. Generally, whitefish somatic growth was slow and most energy was used for gonad growth. Zooplankton had higher total content and different profile of FA compared to benthic macroinvertebrates. Increased zooplanktivory in summer was detected with higher α‐linolenic acid (ALA, 18:3n‐3) and stearidonic acid (SDA, 18:4n‐3) percentage and content as well as increased the ratio of polyunsaturated FAs (PUFAs) of n‐3 and n‐6 family (n‐3/n‐6 ratio) in fish muscle. Whitefish gonadal growth and development occur during the summer growing season and continue until the initiation of spawning in early winter. We found that the content of physiologically crucial PUFA, eicosapentaenoic acid (EPA, 20:5n‐3), docosahexaenoic acid (DHA, 22:6n‐3), and arachidonic acid (ARA, 20:4n‐6) decreased by c. 60% between late summer and the spawning period in early winter. After spawning, total FA content of whitefish muscle increased rapidly, reaching the maximum recorded level in mid‐summer. Intra‐annual changes in whitefish muscle FA profiles and contents were modified both by available diet and reproductive phase; however, reproductive physiology was clearly a stronger driver of the changes in muscle FA composition. Results suggest marked changes in intra‐annual FA composition of fish muscle, an important factor that should be considered in future studies and especially in long term monitoring programs. Future studies are needed to determine whether these inter‐annual FA patterns revealed in this study can be extended to different regions and to e.g. adipose or spring spawning species.

Methods for Extraction of Muscle Proteins from Meat and Fish Using Denaturing and Nondenaturing Solutions

The objective of the present study was to test two extraction methods including solutions with different ionic strengths on the extraction and separation of the myofibrillar proteins from meat and fish muscles of different species. Meat samples from longissimus thoracis muscle of beef and lamb, pectoralis major muscle of chicken, and dorsal white muscle of fish from sole (Solea solea), European hake (Merluccius merluccius), and sea bass (Dicentrarchus labrax) were analyzed. The extraction method using nondenaturing solution led to a major extraction of high molecular-weight proteins as myosin heavy chain, α-actinin, and desmin; on the contrary, the denaturing method provided a good protein extractability of proteins and fragments with low molecular-weight as actin, troponin-T, tropomyosin, and myosin light chain 1 and 2 proteins for the most meat and fish samples. The nondenaturing extraction method showed several advantages resulting in time and labour saving and in minimizing the use of toxic and polluting agents.

Change in Ubiquitin Proteasome System of Grass Carp Ctenopharyngodon idellus Reared in the Different Stocking Densities.

The ubiquitin proteasome system (UPS) is a highly regulated mechanism of intracellular protein degradation and turnover. To evaluate the effect of crowding stress on the UPS in fish, grass carp (Ctenopharyngodon idellus) were randomly reared at low stocking density (LSD, 0.9 kg m−2) or high stocking density (HSD, 5.9 kg m−2) for 70 days. The expression of the genes regulating UPS, stress-related parameters, and profiles of amino acid in white muscle as well as growth rate of fish reared at two stocking densities were investigated. Fish exhibited significantly higher growth rate in the LSD group compared to the HSD group. Serum concentrations of cortisol, total protein, and glucose did not vary significantly in fish between two groups. There was no significant difference in the mRNA levels of nrf2, keap1, and hsp90 in white muscle of fish stocked at two densities at the endpoint of the experiment. In the UPS pathway, the expressions of ub, chip, psmc1 in the LSD group were significantly higher than those in the HSD group (P < 0.05). Ubiquitinated protein level and the content of 3-Methylhistidine elevated significantly in the LSD group (P < 0.05). The mRNA levels of mafbx, murf1, and s6k1 in the LSD group were significantly higher than those in HSD group (P < 0.05). These results illustrate that the fish cultured in lower stocking density would exhibit a greater growth rate and a fast protein turnover in muscle.

Impact of a packing medium with alga Bifurcaria bifurcata extract on canned Atlantic mackerel (Scomber scombrus) quality.

The present research focused on the quality of canned fish. Its primary objective was the quality enhancement of canned Atlantic mackerel (Scomber scombrus) by including an aqueous Bifurcaria bifurcata extract in the packing medium. Various alga extract concentrations were tested and compared with a control without alga extract. After 3 months of canned storage, the cans were opened and quality changes in fish white muscle were analyzed. An inhibitory effect on lipid oxidation development (tertiary compound formation) and color parameter (L* and b*) values was observed as a result of the alga presence in the packing medium. On the contrary, the presence of the alga extract did not produce any effect on volatile compound (total and trimethylamine) formation and lipid hydrolysis (free fatty acid formation) development. A preservative effect derived from the use of an aqueous B. bifurcata extract as packing medium is concluded, and this result is primarily linked to the presence of hydrophilic preservative molecules. The packing system proposed in this work constitutes a novel and promising strategy to enhance the quality of commercial canned fish products. © 2018 Society of Chemical Industry.

Differential Effects of Cod Proteins and Tuna Proteins on Serum and Liver Lipid Profiles in Rats Fed Non-Cholesterol- and Cholesterol-Containing Diets.

Fish muscles are classified into white and red muscles, and the chemical composition of the two fish muscles have many differences. Few reports have assessed the health-promoting functions of white fish muscle proteins (WFP) and red fish muscle proteins (RFP). We therefore evaluated the mechanisms underlying the alteration of lipid profiles and cholesterol metabolism following the intake of WFP prepared from cod and RFP prepared from light muscles of tuna. Male Wistar rats were divided into six dietary groups: casein (23%), WFP (23%), and RFP (23%), with or without 0.5% cholesterol and 0.1% sodium cholate. Compared to the WFP-containing diet, the RFP-containing diet supplemented with cholesterol and sodium cholate significantly increased serum and liver cholesterol contents. However, in the RFP groups, an alteration in cholesterol metabolism including an increased tendency to excrete fecal sterols and hepatic cholesterol 7α-hydroxylase was related to the reduction of hepatic cholesterol contents. This phenomenon might be related to the tendency of an increased food intake in RFP-containing diets. These results highlight the differential effects of WFP and RFP on serum and liver lipid profiles of Wistar rats fed non-cholesterol- or cholesterol-containing diets under no fasting condition.

Ecomorphological divergence drives differential mercury bioaccumulation in polymorphic European whitefish (Coregonus lavaretus) populations of subarctic lakes

Resource polymorphism, whereby ancestral trophic generalists undergo divergence into multiple specialist morphs, is common in salmonid fish populations inhabiting subarctic lakes. However, the extent to which such resource specialization into the three principal lake habitats (littoral, profundal, and pelagic) affects patterns of contaminant bioaccumulation remains largely unexplored. We assessed total mercury concentrations (THg) of European whitefish (Coregonus lavaretus (L.)) and their invertebrate prey in relation to potential explanatory variables across 6 subarctic lakes, of which three are inhabited by polymorphic (comprised of four morphs) and three by monomorphic populations. Among invertebrate prey, the highest THg concentrations were observed in profundal benthic macroinvertebrates, followed by pelagic zooplankton, with concentrations lowest in littoral benthic macroinvertebrates in both lake types. Broadly similar patterns were apparent in whitefish in polymorphic systems, where average age-corrected THg concentrations and bioaccumulation rates were the highest in pelagic morphs, intermediate in the profundal morph, and the lowest in the littoral morph. In monomorphic systems, age-corrected THg concentrations were generally lower, and showed pronounced lake-specific variation. In the polymorphic systems, we found significant relationships between whitefish muscle tissue THg concentration and gill raker count, resource use, lipid content and maximum length, whilst no such relationships were apparent in the monomorphic systems. Across all polymorphic lakes, the major variables explaining THg in whitefish were gill raker count and age, whereas in monomorphic systems, the factors were lake-specific. Whitefish resource polymorphism across the three main lake habitats therefore appears to have profound impacts on THg concentration and bioaccumulation rate. This highlights the importance of recognizing such intraspecific diversity in both future scientific studies and mercury monitoring programs.

Isochoric and isobaric freezing of fish muscle

We have recently shown that, a living organism, which succumbs to freezing to −4 °C in an isobaric thermodynamic system (constant atmospheric pressure), can survive freezing to −4 °C in an isochoric thermodynamic system (constant volume). It is known that the mechanism of cell damage in an isobaric system is the freezing caused increase in extracellular osmolality, and, the consequent cell dehydration. An explanation for the observed survival during isochoric freezing is the thermodynamic modeling supported hypothesis that, in the isochoric frozen solution the extracellular osmolality is comparable to the cell intracellular osmolality. Therefore, cells in the isochoric frozen organism do not dehydrate, and the tissue maintains its morphological integrity. Comparing the histology of: a) fresh fish white muscle, b) fresh muscle frozen to −5 °C in an isobaric system and c) fresh muscle frozen to −5 °C I in an isochoric system, we find convincing evidence of the mechanism of cell dehydration during isobaric freezing. In contrast, the muscle tissue frozen to −5 °C in an isochoric system appears morphologically identical to fresh tissue, with no evidence of dehydration. This is the first experimental evidence in support of the hypothesis that in isochoric freezing there is no cellular dehydration and therefore the morphology of the frozen tissue remains intact.

Copper levels and changes in pH induce oxidative stress in the tissue of curimbata (Prochilodus lineatus)

We analyzed the effect of exposure to 25% 96h-LC50 of copper at low (24.5μgL−1 Cu, pH 4.5), neutral (7.25μgL−1 Cu, pH 7.0) and high pH (4.0μgL−1 Cu, pH 8.0) at 20°C on antioxidant defenses and oxidative stress in the liver, gills and white muscle of the fish Prochilodus lineatus. Water at pH 4.5 and 8.0 affected the enzymatic and non-enzymatic antioxidant systems of the liver and gills, but not of the white muscles of P. lineatus, when compared to water at pH 7.0. After Cu exposure, SOD (superoxide dismutase), GPx (glutathione peroxidase), GR (glutathione reductase) and GST (glutathione S-transferase) activities increased and CAT (catalase) activity decreased in the liver at water at pH 4.5 and 8.0. Meanwhile, the activities of SOD, CAT, GPx, GR and GST increased in the gills at these pHs. SOD and CAT activities increased in the white muscle after Cu exposure at pH 8.0 and GPx, GR and GST activities decreased after Cu exposure at pH 4.5 and 8.0. LPO levels decreased in the liver and gills of fish that were exposed to water at pH 4.5 and 8.0 and, after Cu exposure, the LPO level increased in the liver, gills and white muscle of fish that were exposed to water at pH 4.5 and 8.0, when compared to the control group at pH 7.0. The metallothionein (MT) concentration increased in the liver of fish in water at pH 4.5 and 8.0 and the gill of fish in water at pH 8.0. After Cu exposure, MT in the liver and gills was significantly elevated in fish exposed to water at pH 4.5 and 8.0, but remained at levels similar to the control group in the white muscle. These results indicate a differing sensitivity of fish organs and tissues to essential metals, such as copper, and that toxicity may be relevant at environmental concentrations. These results indicate that the effect of Cu on the response of antioxidant defense systems is determined by water pH.

Antioxidant parameters in fish white muscle as biomarkers of exposure to a cyanobacterial bloom

AbstractThis study examines the responses of antioxidant parameters in the white muscle of four freshwater fish species: Rutilus rutilus (roach), Blicca bjoerkna (white bream), Carassius gibelio (Prussian carp) and Perca fluviatilis (European perch) after exposure to a bloom of Aphanizomenon flos-aquae (Cyanobacteria) in the Gruža Reservoir in Serbia. The set of analyzed biomarkers included the activities of antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR) and biotransformation phase II enzyme glutathione-S-transferase (GST), and the concentrations of total glutathione (GSH) and sulfhydryl (-SH) groups that were measured before and during the bloom. Our results show that SOD activity in C. gibelio and P. fluviatilis, GSH-Px and GST activities in all four fish, GR activity in R. rutilus and C. gibelio and the -SH group concentration in P. fluviatilis markedly decreased during the bloom. The activity of CAT in all four fish and the concentration of GSH in B. bjoerkna and P. fluviatilis significantly increased. The observed changes in nonspecific antioxidant biomarkers in fish muscle (especially CAT, GSH-Px and GST activities) suggest that these parameters could be useful tools in environmental monitoring programs of the freshwater ecosystems where cyanobacterial blooms occur.

Feeding Rates Affect Expression of Heat‐Shock Protein 70 in Green Sturgeon Fry

AbstractTwo growth trials were conducted to determine the effect of feeding rate on the responses of a heat‐shock protein (hsp70) in the fry of Green Sturgeon Acipenser medirostris. Four tanks were randomly assigned to each feeding treatment: 2.5, 5.0, 7.5, 10.0, 12.5 and 15.0% of body weight/d in trial I and 2.0, 3.0, 4.0, 5.0, 6.0 and 7.0% of body weight/d for trial II. The fry were raised indoor at 18°C and fed a commercial salmonid soft‐moist diet. Densities were 50 fry/tank in trial I fed for 49 d posthatch (dph) and 30 fry/tank in trial II fed for 70 dph. At the end of 1 week of feeding, five fish from each tank were subjected to heat shock by increasing the water temperature from 18°C to 28°C at a rate of 4°C/h and then holding at 28°C thereafter for 4 h before tissue samples were collected. Heat shock induced significant changes in the levels of hsp70 in the liver and white muscle of fish in all feeding treatments. However, feeding rate treatments had no significant effect on the basal and heat‐shocked levels of hsp70 in the liver of these fish. The lowest feeding rate significantly depressed the induced level of hsp70 in the muscle of Green Sturgeon. A feeding rate of 10.0% of body weight/d is suggested for Green Sturgeon at 49 dph and 6.0% at 70 dph, based on their maximum responses of hsp70 in white muscle tissue. This study indicates that the response of hsp70 in the liver and muscle of Green Sturgeon is sensitive to heat‐shock stress. The effect of different feeding rates on the response of hsp70 is also tissue‐dependent. This variation should be considered when hsp70 is used as a biomarker to evaluate heat‐shock response.