Transfer of heavy metals from sediment to fish,and their biliary excretion

Uptake and biliary excretion of metals were studied in rainbow trout, Oncorhynchus mykiss, exposed through spiked sediment to a mixture of seven heavy metals. Metal concentrations and toxicity of bile and blood plasma were used as indicators of exposure. Among the seven metals (Cd, Cr, Cu, Hg, Ni, Pb, and Zn) only three (Cu, Hg, and Pb) were concentrated in the bile (bile-plasma ratio >1). Bile-plasma ratios in the rainbow trout were similar to those found in rats for Cu and Hg. Daphnia magna bioassays were used to determine toxicity of bile and blood plasma in the same trout. Toxicity of bile and blood plasma increased after treatment with acid. An analysis of variance (ANOVA) showed that toxicity of bile and blood plasma to D. magna in metal-exposed trout was significantly correlated with (1) bile and blood plasma test concentration, (2) acid treatment of bile and blood plasma (hydrolysis of metal-plasma and metal-bile complexes) and (3) sediment concentration of metals during exposure of trout. In order to significantly detect the magnitude of the exposure to a xenobiotic the biomarker must respond in a dose- or time-dependent manner. Therefore, the potential use of bile toxicity as a biomarker of heavy metal exposure in fish is probably limited by the low bioconcentration of many of these toxicants in bile.     

Characterization of probiotic properties of lactic acid bacteria isolated from an estuarine environment for application in rainbow trout (Oncorhynchus mykiss, Walbaum) farming

Bacterial attachment to fish surfaces and the capacity to compete with pathogens for adhesion sites are essential characteristics in order to select a candidate probiotic for aquaculture. Twelve lactic acid bacteria (LAB) isolated from fish and sediments from Bahía Blanca Estuary, Argentina, were examined for in vitro adhesion to rainbow trout mucus, cell surface properties and competitive exclusion against two salmonid pathogens, Yersinia ruckeri and Aeromonas salmonicida. In order to assess their survival through the digestive tract, pH and rainbow trout bile tolerance were evaluated. All LAB strains survived for 1.5 h incubation in 10% rainbow trout bile. Most of the strains survived 1.5 h at pH 3.0 and three of them showed a reduction of viable counts lower than 2 logarithms, with respect to control (pH 6.5). Only a few strains showed tolerate pH 2.0. All the strains were able to attach to rainbow trout skin mucus (10⁴–10⁶ cells/cm²), to glass (10⁴–10⁵ cells/cm²) and to stainless steel (10³–10⁴ cells/cm²). Sixty percent of LAB strains were capable of competing with and successfully excluding Y. ruckeri and all strains were able to displace it. Against A. salmonicida, 75% of LAB strains competed successfully, 50% were capable of displacing and 60% excluded this pathogen. Our data suggest the potential of these strains as anti-infective agents for use in rainbow trout culture. This study is the first report on the probiotic potential of LAB strains isolated from an estuarine environment from Argentina.     

Magnetic field perception in the Rainbow Trout, <Emphasis Type="Italic">Oncorhynchus</Emphasis> <Emphasis Type="Italic">mykiss</Emphasis>

In this study, we present evidence for the perception of different magnetic field parameters in a facultative anadromous fish species of the family Salmonidae. Magnetic field perception of the rainbow trout, Oncorhynchus mykiss, was demonstrated with a heartbeat conditioning test. The electrocardiogram was measured with subcutaneously inserted silver wire electrodes in freely swimming fish. We demonstrate a conditioned response (i.e. a significant longer interval between two heartbeats) to an intensity/inclination shift for three adult and two juvenile rainbow trouts. Moreover, a conditioned response to a 90° direction shift was demonstrated for three adult and two juvenile trouts. These findings support the hypothesis that the rainbow trout is able to perceive different magnetic field parameters. Furthermore, the study demonstrates magnetosensation in different developmental stages in the rainbow trout, i.e. juvenile and adult fish.     

Habitat use by Nonnative Rainbow Trout, Oncorhynchus mykiss, and Native Little Colorado spinedace, Lepidomeda vittata

We evaluated overlap in microhabitat use between nonnative rainbow trout, Oncorhynchus mykiss, and native Little Colorado spinedace, Lepidomeda vittata, a federally threatened cyprinid, in natural and experimental settings. In natural settings, we also examined occurrence and microhabitat use of two other native fishes, speckled dace, Rhinichthys osculus, and bluehead sucker, Catostomus discobolus. Native species co-occurred, as did rainbow trout and bluehead sucker. However, occurrences of Little Colorado spinedace and speckled dace were not significantly correlated with occurrence of rainbow trout. Total lengths of all three native species were significantly smaller at allopatric sites than at sites sympatric with rainbow trout. Microhabitat characteristics at sites with rainbow trout did not differ from those where the other three species were found, but did differ among the native species. In laboratory experiments with Little Colorado spinedace and rainbow trout, rainbow trout used the lower depth zone most, and spinedace increased use of the lower depth zone upon addition of rainbow trout. In addition, species tended to co-occur in zones, but used cover independently of one-another, suggesting a low level of agonistic interactions. However, after addition of a high density of rainbow trout, spinedace tended to use cover less than before. We suggest that the species can coexist at low rainbow trout densities. Potential negative effects of rainbow trout on Little Colorado spinedace likely increase with increasing densities of rainbow trout, and rainbow trout likely affect smaller size classes of Little Colorado spinedace more than larger ones.     

The population dynamics of eyeflukes Diplostomum spathaceum and Tylodelphys clavata (Digenea: Diplostomatidae) in rainbow and brown trout in Rutland Water: 1974–1978

The development of populations of eyeflukes Diplostomum spathaceum and Tylodelphys clavata in trout introduced into Rutland Water is related to the availability of infected Limnaea pereger, the first intermediate host, and the differential resistance to eyeflukes in Salmo gairdneri and S. trutta. The numbers of snail and fish intermediate hosts were monitored from impoundment of the Gwash in 1974 to completion of the reservoir in 1978. High infection rates in coarse fish in the feeder streams in 1974 are related to high infection rates in Limnaea pereger. Large eyefluke populations in introduced rainbow trout but not in brown trout confirm their differential resistance. Differences in levels of infection in seine-netted and rod-caught rainbow trout suggest that heavily infected fish could not respond to the fishermens' lures. Reduced numbers of eyeflukes in rainbow trout from 1979 onwards are related to the vast increase in volume of the reservoir in 1977 and decrease in abundance of Limnaea pereger.     

Rb-Cs ratio as an indicator of fish diet in lakes of the Patagonia, Argentina

The ratios of Rb to Cs contents were studied in five fish species from seven lakes located in the Patagonia Andean Range, Argentina in order to trace fish diet. The species studied were native velvet catfish (Diplomistes viedmensis) and creole perch (Percichthys trucha), and exotic brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), and brook trout (Salvenilus fontinalis). Rainbow trout specimens from two farms were also studied, as well as fish food items and native mussels (Diplodon chilensis). Rb and Cs concentrations were determined by instrumental neutron activation analysis. A positive correlation of Cs concentration in the muscle of velvet catfish with fish length was observed, probably associated with the long biological half-life of this element in this species, whereas the Rb concentration remained constant, hence inhibiting the use of Rb-Cs ratios as a tracer in this case. Seasonal variations observed for rainbow trout and Cs concentration background bias in one of the lakes studied are also a limiting factor to the use of Rb-Cs ratios as a diet tracer. Rb-Cs ratios allowed clear differentiation of rainbow trout raised in farms from the natural specimens that lived in the same environment, in agreement with Rb-Cs ratios determined in both diets. Rb-Cs ratios in rainbow trout showed significant differences between Rivadavia and Futalaufquen lakes compared to Moreno and Nahuel Huapi lakes, which could be associated with a higher participation of plankton in the diet in the first case. No relevant variations in Rb-Cs ratios of brown trout were observed, probably because of the similarity in the diet.     

Complete cDNA sequence of a rainbow trout IgM gene and evolution of vertebrate IgM constant domains

A complete cDNA clone encoding secreted IgM molecules was isolated from a spleen cDNA library of rainbow trout (Oncorhynchus mykiss). It encodes the leader peptide, VH, DH, JH, and the whole constant region of the secreted IgM molecule. We also studied the copy number of the IgM gene and an unusual RNA splicing mechanism which generates membrane IgM lacking the CH4 domain in rainbow trout. Amino acid sequence comparison of IgM protein sequences from this fish and other vertebrates indicates that some domains of IgM have evolved at a relatively constant rate. The evolution of salmoid fish including divergence time is discussed.     

A preliminary assessment of the impact of alien rainbow trout (Oncorhynchus mykiss) on indigenous fishes of the upper Berg River,Western Cape Province,South Africa

Impacts of alien rainbow trout (Oncorhynchus mykiss) on critically endangered Berg River redfin (Pseudobarbus burgi), Cape kurper (Sandelia capensis) and Cape galaxias (Galaxias zebratus) in the upper Berg River were investigated in terms of predation and spatial interactions. Trout stomach contents revealed that invertebrates dominate trout diet within the study area, whilst only six fish were recovered from 45 stomachs. The apparent low fish predation success of O. mykiss within the stream suggests a smaller impact compared to that of other alien piscivores such as bass (Micropterus spp.). Galaxias zebratus was the only fish species identified as prey, and its conservation status in the river requires further investigation. Snorkelling surveys revealed that rainbow trout co-exist with S. capensis and adult P. burgi within pools on this river. Galaxias zebratus was absent from the pools, while P. burgi juveniles were segregated from rainbow trout along a depth gradient, possibly indicating avoidance behaviour. Sandelia capensis juveniles may avoid predation by hiding under rocks. Rainbow trout probably compete with indigenous fish for food and space in the pools, though this could not be quantified. The impacts of O. mykiss on all indigenous fauna within the river are likely to be density-dependent.     

The excretion pattern of biliverdin and bilirubin in bile of the small skate (Raja erinacea)

Summary Bile pigment composition (biliverdin, bilirubin and their conjugates) was analyzed in stored gallbladder bile and newly synthesized hepatic bile from the small skate (Raja erinacea). During a five day period of captivity, gallbladder volume remained relatively constant while bilirubin and biliverdin content increased two to three fold. Biliverdin which accounted for 50% of the pigments did not increase as a percentage of tetrapyrroles during this period. The relative proportion of bilirubin and its conjugates also remained constant, averaging 65% for bilirubin monoglucuronide, 30% for bilirubin diglucuronide and 5% for unconjugated bilirubin as measured by HPLC methods. Intravenous administration of biliverdin resulted in significant increases in the biliary excretion of both biliverdin and all bilirubin tetrapyrroles. Insignificant quantities of³H-biliverdin were detected in hepatic bile following the intravenous administration of³H-bilirubin. These studies indicate that the small skate excreted both biliverdin and bilirubin conjugates in bile and that the biliverdin was not produced by in vitro oxidation of bilirubin or its metabolites.     

Effects of Saccharomyces cerevisiae supplementation on immune response,hematological parameters,body composition and disease resistance in rainbow trout,Oncorhynchus mykiss (Walbaum, 1792)

Natural substances are now generally preferred over chemical and synthetic compounds for the growth and immune enhancement of aquatic organisms. The aim of this study was to evaluate the effect of Saccharomyces cerevisiae extract and hydrolyzed powder on immunity, hematological parameters and body composition in rainbow trout, Oncorhynchus mykiss. Six hundred rainbow trout (50 ± 5 g mean weight) were acclimated to laboratory conditions and then randomly divided into four groups of triplicate tanks. The first group was fed with a commercial diet (control) without supplementation. The second and third groups were given a diet supplemented with 1% of yeast extract and hydrolyzed powder, respectively. The fourth group was also fed with a basal diet supplemented with 0.5% of both substances. Fish were cultured in 300‐L polyethylene tanks for 60 days; immune and hematological parameters, fillet composition and disease resistance were analyzed at days 0, 30 and 60. Results showed that a combination of Saccharomyces cerevisiae extract and hydrolyzed powder could improve the immunity and alter hematological parameters of the rainbow trout compared to the control. Mortality rates of fish fed yeast extract and hydrolyzed powder were also lower than in fish fed the control diet after challenging with Yersinia ruckeri. There were no significant changes in rainbow trout fillet composition compared to the control. It can be concluded that fish diet supplementation with a mixture of yeast extract hydrolyzed powder is preferable compared to each one used alone.     

Redd superimposition by introduced rainbow trout,oncorhynchus mykiss, on native charrs in a japanese stream

Spawning redd superimposition of introduced, spring-spawning rainbow trout,Oncorhynchus mykiss, on native, fall-spawning Dolly varden,Salvelinus malma, and white-spotted charr,S. leucomaenis, were examined in a small stream in Hokkaido, Japan. The stream reaches in which Dolly Varden and white-sported charr redds were observed in fall 1997 greatly overlapped with the reaches in which rainbow trout redds were recorded in spring 1998. Spawning microhabitats were also similar between trout and the two charr species. Thirteen and 3% of Dolly Varden and white-spotted charr redds, respectively, were superimposed by rainbow trout redds. The eggs or alevins in the disturbed charr redds were potentially damaged because charrs were not likely to have emerged from the redds before the superimposition occurred. In sufficiently great abundance, introduced rainbow trout may negatively impact native charr populations by dislodging the latter’s spawning redds.     

An outbreak of phaeohyphomycosis in rainbow trout caused by Scolecobasidium humicola

A previously undescribed host for the opportunistic dematiaceous hyphomycete, Scolecobasidium humicola, is reported. Several epizootics among rainbow trout, Salmo gairdneri, occurred in a Tennessee fish hatchery from 1969 to 1973. Symptoms included surface lesions, blisters and abscesses. The kidneys and other internal organs were invaded by the mycelium of S. humicola. Tissue morphology of the fungus was typical of that associated with phaeohyphomycosis. Experimental infections were reproduced in fingerling rainbow trout after intraperitoneal inoculation of S. humicola. Following a change in the hatchery's water supply, no new epizootics have occurred.     

Anthropogenic influences on population sizes, age and growth of naturalized rainbow trout, Oncorhynchus mykiss, in Kenya

Riverine fishery in Kenya has witnessed profound changes since the 1950s, especially after independence (in 1963) when watersheds on the south‐eastern slopes of Mt Kenya were opened up for settlement. In particular, rainbow trout populations have declined essentially resulting from anthropogenic changes through over‐exploitation and/or degraded habitats. While there still are self‐sustaining rainbow trout populations in this stream among others they are in decline an indication that changes that have occurred on the watershed have altered their sizes, age and growth. The study was carried out in the Sagana, a third‐order stream, which rises at about 4000 m altitude on the south‐eastern slope of Mt Kenya, to obtain and document information on population sizes, age and growth of rainbow trout populations and to relate them with those recorded in the 1950s when trout streams were pristine (with little human influence). Stations were fished bi‐monthly from 1996 to 1998 and later for 6 months in 2002. Information on age and growth was obtained by use of annual marks, tagging fish of known age, and by validating their age using captive fish of known age. The minimum mean back‐calculated length at age for age one rainbow trout was 13.09 cm in upstream station and 15.10 cm for downstream stations. However, there was no significant difference in mean back‐calculated lengths at age for all years between fish in upstream and downstream stations (t‐test, t = −0.01, P = 0.99). Although female fish showed higher mean annual back‐calculated length increments than males, there was no significant difference in mean back‐calculated lengths at age between sexes (t‐test, t = −0.27, P = 0.80). The rate of growth in length was rapid for 1‐year‐old fish and declined in the second and third years. This study observed that most of the fish were small with only a few reaching more than 2 years of age because of overfishing. There are good reasons for optimism about the future of trout populations in this stream but concerted efforts are required to rehabilitate them. If trout populations are to increase, a management strategy is required to reduce fishing pressure and to maintain stream fishery against competing needs for resources in the catchments.     

Study of the heme catabolism of fish

• 1.1. The composition of bile pigments in the blood and bile of 39 species were studied.
• 2.2. Conjugated bilirubin (trace to 4.62 mg/100 ml) was detected in the serum of most fish, while biliverdin (trace to 2.0 mg/100ml) was detected only in Anguilla Japonica, Thalassoma lunare and Clinocottus analis.
• 3.3. Analysis showed tht there are two types of bile pigments excretion pattern in these fishes. The first pattern excretes bilirubin (most conjugate) predominantly, the other excretes mostly biliverdin with some bilirubin. However, during starvation, the excretion of conjugate bilirubin gradually shifted to unconjugated biliverdin. The rate of shifting varies with species.
• 4.4. Introduction of bilirubin into Anguilla japonica produced an initial excretion of mono-conjugates, followed by di-conjugates. Introduction of biliverdin caused an increased in the excretion of unconjugated biliverdin, but no significant increase of bilirubin in the bile was detected.
• 5.5. A binary excretion pathway of bile pigments in fish is proposed. The evolutionary characteristics of heme catabolism in terrestrial animals with respect to this pathway is discussed.

     

Limestone Treatment of Whetstone Brook, Massachusetts. II. Changes in the Brown Trout (Salmo trutta)and Brook Trout (Salvelinus fontinalis)Fishery

Density, age structure, and growth rates of wild brook trout (Salvelinus fontinalis)and brown trout (Salmo trutta)in Whetstone Brook in northcentral Massachusetts were monitored for 4 years before and 3 years during limestone treatment to mitigate acidic conditions. The population density of brook trout increased significantly during treatment. Liming did not have any significant effects on the growth rates of brook trout or brown trout. Actual survival rates of brook trout and brown trout were not calculated due to the low density of both species, but more older individuals of both species were captured during the treatment period. Fulton condition factors (an index of fish condition) increased significantly for both brook trout and brown trout during treatment. Seven-day in situ bioassays of brown trout and rainbow trout demonstrated that liming improved the chemical environment for fish in Whetstone Brook. During a pretreatment bioassay in 1987, 100% rainbow trout mortality was observed at both the control and treatment stations in Whetstone Brook. Brown trout mortality was 67% in the control station and 70% in the treatment station. The pH during the 1987 bioassay averaged 4.90 in the control station and 4.99 in the treated station. During a bioassay conducted in 1990 after treatment began, rainbow trout mortality was 100% in the control station and 0% in the treatment station. Brown trout mortality was 17% in the control station and 0% in the treatment station. The pH during the 1990 bioassay averaged 5.23 in the control station and 6.60 in the treatment station. Analysis of total aluminum in the gills of fish from the 1990 bioassay revealed higher levels in fish from the control station than in those from the treatment station.     

Trace Metal Levels in Rainbow Trout (Oncorhynchus mykiss) Cultured in Net Cages in a Reservoir and Evaluation of Human Health Risks from Consumption

Although fish consumption has positive health effects, metals accumulated in fish can cause human health risks. In this study, the levels of ten metals in rainbow trout (Oncorhynchus mykiss) farmed in the Keban Dam Reservoir, which has the biggest rainbow trout production capacity in Turkey, were determined and compared with the maximum permissible levels (MPLs). Also, human health risks associated with rainbow trout consumption were assessed. The metal concentrations in rainbow trout were found below the MPLs. The estimated daily intake of each metal was much lower than the respective tolerable daily intake. The target hazard quotient (THQ) for individual metal and total THQ for combined metals did not exceed 1, indicating no health risk for consumers. The cancer risk (CR) value for inorganic arsenic was within the acceptable lifetime risk range of 10⁻⁶ and 10⁻⁴. For carcinogenic and non-carcinogenic effects, the maximum allowable fish consumption rates were high enough to ensure the human health. According to these results, the consumption of rainbow trout farmed in the Keban Dam Reservoir does not pose a risk on human health.

     

Induction of vitellogenin production in male tilapia (Oreochromis mossambicus) by commercial fish diets

Mozambique tilapia, (Oreochromis mossambicus), are a euryhaline teleost and an important biological model species. Captive male tilapia frequently have high levels of the estrogen-induced yolk precursor protein vitellogenin (Vg), a common indicator of exposure to estrogenic compounds. Sex steroids are found in commercial fish diets, but relatively few studies have examined the relationship between commercial diets and Vg production. In a fasting experiment to ascertain a dietary role in male Vg production, plasma Vg was reduced to negligible levels after 2 weeks of fasting, while no change in estrogen receptor (ER) expression was seen. When male tilapia were fed a squid-based diet that replaced the commercial trout diet, plasma Vg was reduced to undetectable levels over 40 days, concomitant with significant reductions in hepatic expression of Vgs A, B, and C, and ERβ, compared with control fish fed commercial trout diet. Female tilapia fed the squid-based for 20 days had no change in these parameters. When male tilapia were fed a defined, soy-based diet, plasma Vg reduced to 20% of levels in fish given either commercial trout diet or a defined, fishmeal-based diet. Overall, results from these studies suggest that estrogens in a commercial trout diet induce vitellogenin production by increasing expression of Vg, but not ER genes in male tilapia.