A comparison of the differential accumulation of cadmium in the tissues of three species of freshwater fish, Salmo gairdneri, Rutilus rutilus and Noemacheilus barbatulus

Roach and stone loach were exposed to cadmium dissolved in their aquarium water at 500 and 1250 micrograms/l, respectively, and the distribution of the metal accumulated in the major body organs was determined. The pattern of distribution for each species was somewhat different and was distinct in each case from that observed previously with rainbow trout. The total body loads of cadmium accumulated by the three species were assessed during the period of exposure and found not to correlate directly with the concentration of cadmium to which the individual species had been exposed. An alternative comparator was devised which as the quotient of the total body cadmium accumulation (microgram/100 g body wt) and the notional cadmium dose (microgram/l) X weeks was described as a fractional retention coefficient for cadmium. The coefficient was constant for each species at different periods of exposure to cadmium alone. The values of the coefficient for roach and stone loach were however much lower than that for rainbow trout. When rainbow trout were preexposed to zinc (100 micrograms/l, 5 days) before being exposed to cadmium, the fractional retention coefficient for cadmium fell to a value similar to those seen with roach and stone loach exposed to cadmium alone. The significance of these observations in relation to the nature of the intracellular proteins to which cadmium is bound in the three species is discussed in the light of their differential susceptibility to the toxic effects of cadmium.     

Sequestration of environmental cadmium by metallothionein in the roach (Rutilus rutilus) and the stone loach (Noemacheilus barbatulus)

Two species of coarse fish that are relatively resistant to cadmium poisoning were exposed to sub-lethal concentrations of the metal in their aquarium water. Thus, roach were exposed to cadmium concentrations between 30 and 500 micrograms/l for periods of 14-70 days whereas stone loach were exposed to 1250 micrograms Cd/l for 21-77 days. Under all conditions of exposure, it was found upon analysis of the major organs of accumulation of cadmium in the two species that the toxic metal was sequestered by a single isoform of metallothionein. The amino acid compositions of roach and stone loach metallothionein were determined and found to be similar to those reported for other piscine metallothioneins. The two proteins were found to contain Cd:Zn:Cu in approximate ratios of 4:1:2 per mole of protein. The sequestration of Cd by metallothionein in the two resistant species of fish is contrasted with the situation observed previously in a cadmium-sensitive species, the rainbow trout.     

Induction of metallothionein gene expression by cadmium and the retention of the toxic metal in the tissues of rainbow trout (Salmo gairdneri)

1. When rainbow trout were exposed to cadmium by intraperitoneal injection, there was a rapid (within 3hr) and significant (approx. 63%) loss of the metal from the whole bodies of the fish.2. Of the metal retained in the bodies of the fish (approx. 37% of the injected dose), more than 98% was accounted for collectively among the liver, kidney and gills.3. Subsequent maintenance of the rainbow trout in fresh water for up to 98 days post-metal administration, indicated that there was no further loss of the cadmium accumulated in the organs studied and that the distribution of the metal among the liver, kidney and gills remained unchanged over that period.4. During this 98-day period of maintenance of the fish, tissue concentrations of metallothionein-specific mRNA and metallothionein protein were quantified using riboprobe and ELISA systems respectively. Metallothionein-specific mRNA concentrations increased rapidly (within 24 hr) before falling back to levels similar to, or slightly greater than, those found in control animals. The concentration of metallothionein protein also increased significantly (within 3 days) then remained elevated thereafter.5. Throughout the experimental period, the concentrations of zinc and copper were also monitored in the liver, kidney and gills of the rainbow trout. The concentrations of each ion differed between each of the organs but did not change during the experiment.6. The induction of metallothionein gene expression by cadmium in the liver, kidney and gill of rainbow trout and the subsequent sequestration of the toxic metal is discussed with regard to the relative levels of these other essential metal ions.     

Crystallization of the rainbow trout (Salmo gairdneri) haemoglobin IV

Crystals of rainbow trout (Salmo gairdneri) haemoglobin IV were grown in mini batches from a solution of ammonium sulphate. Large single crystals grew over five days and were up to 2 mm in length. X-ray diffraction experiments indicated a space group of C222(1) with unit cell dimensions of a = 85.3 A, b = 94.6 A and c = 105.7 A. The crystals diffract to better than 2.5 A but exhibit some mosaicity along the c axis.     

Organ distribution of aldehyde dehydrogenase activity in the rainbow trout (Salmo gairdneri Richardson)

1. Aldehyde dehydrogenase activity was measured in gills, muscle, brain, intestine, kidney, heart and liver of rainbow trout, using 3,4-dihydroxyphenylacetaldehyde (the biogenic aldehyde derived from dopamine) as the substrate. 2. Aldehyde dehydrogenase activity was found to be present in all of the organs studied. 3. The highest activity was found in the liver (276 nmol/min.g wet wt of tissue). 4. A remarkably high activity was found in the heart (117 nmol/min.g). 5. The gills showed the lowest activity (1.9 nmol/min.g).     

Some blood parameters of the rainbow trout (Salmo gairdneri Richardson)

Some of the blood constituents of male, female and immature rainbow trout of the Shasta variety, maintained in known environmental and dietetic conditions, were examined and the results statistically treated. The parameters for male and female trout were similar, only the erythrocyte count exhibiting a significant difference. Large but expected differences were evident between the parameters for mature and immature fish.     

Metabolic utilization of diets by polyploid rainbow trout (Salmo gairdneri)

1. Nitrogen (NH4) excretion and oxygen consumption were measured in four groups of juvenile rainbow trout (36-40 g): triploids obtained by a heat shock treatment (3n); triploids obtained by mating diploid females with tetraploid males (3n/4n); tetraploids (4n) and a diploid control (2n). 2. No differences in daily N excretion patterns and in N excretion rate measured as a percentage of N intake were detected between groups. 3. Oxygen consumption of the 2n group was significantly inferior to that of the 3n and 4n groups but not to the 3n/4n group. 4. SDA, specific dynamic action (measured as a percentage of the energy intake), ranged from 5.6 to 8.6% and was not different between groups. 5. Protein energy catabolism measured as per cent of total energy expenditure was significantly higher in the 2n group than in polyploid groups.     

Postspawning mortality of rainbow trout (Salmo gairdneri) associated with Lactobacillus

A Lactobacillus sp. was consistently isolated from dead and moribund postspawning brood stock rainbow trout. Pathology was characterized by massive chronic inflammation throughout the abdominal cavity and formation of pseudomembranes. The bacteria were most abundant in spent testes. Repeated handling was considered to be the major stressor leading to this infection and subsequent high mortality.     

The characteristics and distribution of monoamine oxidase (MAO) activity in different tissues of the rainbow trout, Salmo gairdneri

Monoamine oxidase (MAO) activity was determined fluorometrically in brain, intestine, kidney and liver tissues of the rainbow trout, Salmo gairdneri. MAO activity was inhibited by various drugs in a concentration-related manner, with single sigmoid inhibition curves, the inhibitors of type A MAO, harmaline and clorgyline being more effective than deprenyl, an inhibitor of type B MAO. Intestine exhibited greatest MAO activity followed by liver and brain with kidney showing least activity. The Michaelis constants (Km) also showed variability between tissues. Inhibition of MAO by harmaline was non-competitive and dependent on the concentration of substrate present.     

Microvasculature of the pineal organ of the rainbow trout (Salmo gairdneri)

Summary The angioarchitecture of the pineal organ of the rainbow trout (Salmo gairdneri) was investigated by means of the corrosion-cast preparation method and scanning electron microscopy. Two main arteries (aa. epiphyseales) supply the pineal parenchyma. They emerge from the aa. cerebri anteriores and run in the fissure between the prosencephalon and the mesencephalon. After entering the pineal stalk, the aa. epiphyseales branch off into several arterioles, most of which extend to the pineal end-vesicle where they give rise to a lobular, bilaterally symmetric capillary network. Capillaries establishing the main portion of the pineal vessels appear widened in comparison to those supplying other portions of the brain and resemble capillaries in other endocrine organs. In Salmo gairdneri, no specialized system of portal vessels appears to exist between the pineal organ and other portions of the brain.     

Seasonal changes in reproductive function of the rainbow trout (Salmo gairdneri)

The sequential changes in serum oestradiol 17β (measured by specific radioimmunoassay), vitellogenin (measured by phosphoprotein phosphorus content) and total calcium (measured by fluorimetry) in male and female rainbow trout under a simulated natural photoperiod cycle were investigated. Resting levels of 130 pg/ml serum oestradiol in both male and female fish were found in April and May. In the female, levels reached a peak of 4800 pg/ml in October, and almost returned to resting levels just prior to spawning in mid-January. No significant change from resting levels was seen in the male fish.
In both male and female fish levels of 25 μg/ml serum phosphoprotein phosphorus and 10–14 mg % total serum calcium were found from April to July. Coincident with the rise in oestradiol 17β, in the females serum levels of phospho-protein phosphorus and total calcium increased to 400 uβg/ml and 58 mg% respectively just prior to spawning. In the males no significant change in either of these values was observed throughout the cycle. These results strongly support the hypothesis that photoperiod is the major factor in the environmental control of reproductive activity in the rainbow trout.     

Ultrastructural development of the saccus vasculosus in rainbow trout (Salmo gairdneri)

Summary The morphology of crown cells and supporting cells of the saccus vasculosus has been described by numerous investigators. A third type of cell has been mentioned by several authors and referred to variously as undifferentiated crown cells, pseudo-coronet cells, pear-shaped cells and, most recently, as liquor-contact neurons. A developmental study of the organ was undertaken as a possible means of characterizing this third cell type and determining its origin.The epithelium of the saccus vasculosus and the ependyma of the third ventricle are different and distinguishable at the time of hatching in rainbow trout. Initially, apical protrusions from crown cells extend slightly into the lumen and a few end knobs or motile cilia project from them. Basal bodies with cross-striated rootlets occur frequently. In swim-up fry, end knobs are more numerous and heavily vacuolated, although cross-striated rootlets are less apparent.Evidence is presented that is consistent with a hypothesis of secretory activity in the crown cells. Further, portions of end knobs containing this material appear to be pinched off from the remainder of the crown cell. The possible presence of bipolar neurons is also discussed.Supported by Research Grant 5 R01 NS0627 from the National Institute of Neurological Diseases and Stroke.     

Functional morphology of the bulbus arteriosus of rainbow trout (Salmo gairdneri Richardson)

The rate of expansion in volume of the bulbus arteriosus with increase in pressure is measured. From this it is calculated the elastic rebound of the bulbus can account for approximately 25 % of blood flow in the ventral aorta; this proportion decreases as cardiac output increases. The structure of the wall of the bulbus is shown to consist of a compact outer layer with a series of separate longitudinal elements on the inner surface. These elements are connected to the compact layer by numerous radial fibres. This structure equalizes strain in all the structural elements of the wall during large changes in volume. Evidence is discussed which shows that the bulbus arteriosus in teleosts is morphologically and biochemically distinct from the ventral aorta. The bulbus is probably of cardiac origin rather than an expansion of the posterior end of the aorta as generally supposed.     

Degradation of extracellular thymidine by cultured hepatocytes from rainbow trout (Salmo gairdneri)

1. Trout hepatocytes cultured as attached monolayers had low rates of [3H]-thymidine ([3H]-TdR) incorporation during replicative or repair synthesis of DNA. 2. Within 2 hr, most [3H]-TdR was metabolized by trout hepatocytes to a major product that eluted in advance of intact [3H]-TdR on Sephacryl S-200 columns. 3. Metabolism of [3H]-TdR by trout hepatocytes rapidly destroyed its ability to label replicating indicator cultures of proliferating rat hepatocytes. 4. These studies demonstrate that [3H]-TdR tracer assays for DNA synthesis cannot be reliably used in cultured trout hepatocytes which catabolize thymidine much more rapidly than do rat hepatocytes.