The effect of water pH on swimming performance in rainbow trout (Salmo gairdneri,Richardson)

A Brett-type respirometer was used to measure the effect of water pH on swimming performance of rainbow trout (Salmo gairdneri). Variations in water pH between 6 and 9 had no measurable effect on maximum aerobic swimming speed. At water pH 4, 5, and 10, however, the critical velocity was only 55, 67, and 61% respectively of that recorded for fish in water of pH 7. Exposure to acid conditions increased coughing and breathing frequency. Acid exposure resulted in a decrease whereas alkaline exposure resulted in an increase in both whole blood and red blood cell pH. Blood gas and acid-base characteristics showed little change during swimming at 2.0 BL/second, but exhaustive swimming resulted in a marked and immediate drop in blood pH in fish in acid, alkaline and neutral water. The blood acid-base status was restored to resting levels after exercise in neutral and alkaline water, but the acidosis was maintained following exercise in acid water. Fatigue occurred earlier and blood lactate levels increased to a higher level in fish swum to exhaustion in acid or alkaline water, compared with fish in neutral water.     

Strawberry disease in rainbow trout, Salmo gairdneri Richardson

Abstract. Strawberry disease is a subchronic, non–debilitating, and non–fatal inflammatory skin disease of rainbow trout that has been recognized for the past 25 years. Morbidity ranges up to 80% and the disease affects fishes from 15cm in length to brood stock size. Epizootiological data indicate that strawberry disease usually appears, first in the autumn and reaches peak incidence during the following winter and spring. Data also indicate that the disease is found only in certain trout farms in the western and Pacific north–western regions of the United States. Although the cause of strawberry disease is unknown, the normal clinical course of 8 weeks can be reduced by oral treatment with oxytetracycline. Clinical signs include appearance of bright red, raised, circumscribed, ulcerated and indurated lesions in the skin that usually range up to 3 cm or more in diameter. Microscopically, the disease is characterized as a subchronic, focal, non–suppurative dermatitis with ulceration and extensive infiltration of mononuclear inflammatory cells.     

The liver parenchymal cells of rainbow trout (Salmo gairdneri) endocytose mannose-terminated glycoproteins

A mannose-terminated glycoprotein,¹²⁵I-invertase, was taken up and degraded by isolated rainbow trout liver cells at 12°C. The uptake was inhibited by EGTA and no degradation occurred in the presence of ammonium ions. The liver cell suspension was fractionated by differential centrifugation in parenchymal and nonparenchymal cells, respectively. The parenchymal liver cells seemed to be the most active cells in uptake of labelled invertase bothin vitro andin vivo. Only negligible amounts of ligand were recovered in the nonparenchymal cells. Internalization of¹²⁵I-invertase at different temperatures was demonstrated indirectly by releasing surface-bound ligand with EGTA. Ligand was internalized even at 0°C in trout liver cells.In vitro uptake of¹²⁵I-invertase was inhibited by excess unlabelled invertase, by mannan and by N-acetylglucosamine.These data suggest that invertase is endocytosed by a mannose-specific pathway by the parenchymal liver cells of rainbow trout.     

Immunoglobulin heterogeneity in the rainbow trout, Salmo gairdneri Richardson

Abstract. Hetereogeneity of rainbow trout immunoglobulins was demonstrated by using monoclonal antibody 1A6 and polyacrylamide-gradient gel electrophoresis. Immunoglobulins defined by elisa using monoclonal antibody 1A6 were about 30% of the total immunoglobulins, detected by elisa using polyclonal antibodies, in healthy rainbow trout. In trout obtained from farms with a previous history of infectious viral diseases, 1A6-immunoglobulins were only about 14% of the total. Several serum pools from infected trout could be totally depleted of 1A6-immunoglobulins (about 12% of total immunoglobulins) by affinity chromatography over Sepharose immobilized monoclonal antibody 1A6. Polyacrylamide-gradient gel electrophoresis under denaturing conditions of total immunoglobulins, 1A6 immunoglobulins and no-1A6 immunoglobulins purified by affinity chromatography, showed a majority heavy chain of 70 KDa and a minority heavy chain of about 60 KDa, two light chains of 24 and 26 KDa, and a 11–14 KDa polypeptide.     

Control of gallbladder motility in the rainbow trout,Salmo gairdneri

Immunohistochemistry revealed nerves containing VIP-like and 5-HT-like material in both gallbladder wall and bile duct of the rainbow trout, while endocrine cells containing gastrin/CCK-like and substance P-like material were present in the mucosa of the bile duct and the duodenum. Fluorescence histochemistry showed adrenergic nerves close to the muscle layer of the gallbladder.Sulphated CCK8, caerulein and non-sulphated CCK8 (in this order of potency), 5-HT and acetylcholine were excitatory on isolated strip preparations, while VIP and adrenergic agonists were inhibitory. The adrenergic drugs were probably actingvia a beta-adrenergic receptor, while the effects of 5-HT and cholinergic drugs were antagonized by methysergide and atropine respectively.Electrical stimulation of the gallbladder nervesin situ failed to show any effect or under certain conditions induced a rebound effect.It is concluded that the motility control of the rainbow trout gallbladder may involve an inhibitory innervation by adrenergic and possibly VIP-releasing nerves, while 5-HT, acetylcholine and a CCK-like substance may be involved in the excitatory control.     

Behaviour of rainbow trout, Salmo gairdneri Richardson, in marine cages

Abstract. Underwater television was used to observe the distribution and swimming behaviour of groups of farmed rainbow trout, Salmo gairdneri Richardson, in marine net cages. Undisturbed rainbow trout (mean total length 240 mm) aggregated near the surface, remaining motionless in slack water and formed polarized shoals at higher current velocities. Larger fish (mean total length 317 mm) occupied deeper parts of the cage and were more active during periods of slack water. The results are compared with previous work on farmed Atlantic salmon, Salmo salar L., and discussed in relation to the biology of wild rainbow trout and recent work on exercise, growth and condition in salmonids.     

The pathology of chronic ammonia toxicity in rainbow trout, Salmo gairdneri Richardson

Abstract. Two groups of rainbow trout fingerlings were exposed for 90 days to 0.2 and 0.4 mg/1 of un-ionized ammonia, respectively. Several fish exposed to the higher concentration soon developed clinical signs suggestive of a neurological dysfunction but subsequently recovered. No lesion attributable to ammonia was seen in the gills of any of the fish. This raises questions about the precise role of ammonia in the production of gill diseases in intensively cultured trout.     

Thyroidal compensation in rainbow trout (Salmo gairdneri) fed canola meal

Rainbow trout (Salmo gairdneri Richardson) were fed either a soybean mealbased (SM) or canola meal-based (CM) diet for up to 20 weeks. Plasma thyroxine (T₄) and triiodothryonine (T₃) levels were significantly lower in the CM-fed fish sampled after 12 weeks. However, there appeared to be some compensation after 12 and 20 weeks in that the thyroid hormone levels in trout fed the CM were not significantly different from those of the SM-fed fish. Nevertheless, there was marked thyroid hyperplasia and hypertrophy in the CM-fed fish sampled at 12, 16 and 20 weeks after commencement of the experiment. Moreover, the growth rate was significantly lower in the CM-fed fish in comparison to the SM-fed fish throughout the 20 week study period.Plasma T₄ levels were similar in SM-fed fish sampled 12, 16 and 20 weeks after commencement of the experiment, but plasma T₃ levels progressively increased over this period, as did the apparent activity of the thyroid tissue based on histological criteria.Fasting for up to 8 weeks resulted in the arrested growth of the SM-fed fish, and a loss in body weight of the CM-fed animals over the 8 week period of the fast. In addition, the plasma thyroid hormone levels in the fasted fish tended to be lower than in fish fed both the SM and CM diets prior to fasting, and there was histological evidence indicating a reduced activity of the pituitary-thyroid axis. However, thyroid hyperplasia and hypertrophy were still evident in the fasted fish previously fed the CM diet indicating that the adverse affects of CM diets are not completely reversible after 8 weeks.In fish fed the CM diet for 12 weeks and then the SM diet for up to a further 8 weeks (diet C-S) there was a compensatory increase in plasma thyroid hormone levels evident within 4 weeks after the change in diet, but no apparent decrease in thyroid hyperplasia or hypertrophy. In addition, in the fish fed the C-S diet there was a marked compensatory growth rate, and an increased feed: gain ratio; body weights of this group of fish were not significantly different from those of the SM-fed animals after 20 weeks of study, indicating a considerably higher growth rate over the last 8 week period.     

Dietary carbohydrate and growth,body composition and heat increment in rainbow trout (Salmo gairdneri)

A study was conducted to determine growth, body composition and heat increment (HI) of rainbow trout reared on isonitrogenous high digestible carbohydrate (HC) and high fat (HL) diets at 15°C. Trout reared on the HC diet had a significantly lower final body weight and carcass lipid content and a significantly higher feed:gain ratio and carcass protein content than trout reared on the HL diet after 12 weeks on the test diets. The lower carcass lipid composition indicates that trout do not readily convert dietary carbohydrates into fat. HI of trout reared on the HC diet was significantly higher than that of fish reared on the HL diet. Considering the poor utilization of dietary carbohydrates as an energy source and the apparently low conversion of dietary glucose into fat, the cause of the higher HI associated with the HC diet is not completely understood. However, it is possible the elimination of excess dietary glucose is an energy dependent process resulting in an increased heat production which would partly account for the increased HI. Furthermore, if the HC diet is a low net energy diet, then the metabolism and utilization of dietary and tissue proteins (amino acids) for energy by the trout may also be partly responsible for the increased HI of the trout reared on the HC diet.     

Interactions among dietary minerals,arginine and lysine in rainbow trout (Salmo gairdneri)

Studies were conducted to determine whether interactions occur among dietary lysine, arginine and monovalent minerals in rainbow trout. In one experiment, rainbow trout fingerlings were fed diets containing three levels of lysine (2.4, 3.1 and 3.8 g per 100 g diet), two levels of arginine (1.7 and 2.5 g per 100 g diet) and two mixtures of Na⁺ K⁺ and Cl in a 3×2×2 factorial design. The mixtures varied in the proportions of cations to anions such that Cl equalled the sum of Na⁺ and K⁺ (cations – anions = 0 mEq/kg diet) in one mixture and exceeded the sum of Na⁺ and K⁺ (cations – anions = –200 mEq/kg diet) in the second mixture. Growth and efficiency of feed conversion were not affected by dietary lysine and arginine in fish fed diets containing – 200 mEq/kg balance, but when fish were fed diets containing a 0 mEq/kg balance, 3.8% lysine and a combination of 3.1% lysine and 2.5% arginine depressed both measures of response. Trout receiving the 0 mEq/kg cation-anion balance had significantly higher free histidine concentrations and lower free lysine concentrations in muscle and higher hepatic arginase activity (P0.01) than those receiving –200 mEq/kg. In another experiment, trout were fed diets containing three levels of K⁺ (21, 191 and 360 mEq/kg), two levels of Na⁺ (21 and 191 mEq/kg) and two levels of Cl^– (179 and 347 mEq/kg) in a 3×2×2 factorial design. Growth and efficiency of feed conversion were depressed and hepatosomatic index increased with higher levels of dietary K⁺ (P0.01), Na⁺ (P0.05) and Cl (P0.01), with significant K⁺ x Cl⁺ (P0.01) and K⁺ x Na⁺ x Cl (P0.05) interactions. Increasing dietary K⁺ resulted in increased levels of muscle free histidine and decreased levels of muscle free lysine and arginine (P0.01), while increasing dietary Cl increased muscle free lysine, the effect of which was dependent on dietary potassium (K⁺ x Cl^–, P0.01). It is concluded that dietary levels of K⁺, Na⁺ and Cl^–, irrespective of overall cation-anion balance of these minerals, affects growth rate, efficiency of feed utilization and the metabolism of basic amino acids in tissues of trout. Excess lysine causes depressed growth and efficiency of feed utilization. These effects were due to a lysine toxicity rather than a lysine-arginine antagonism, as they were not prevented by supplemental dietary arginine.     

Phagocytic cells in the epidermis of rainbow trout, Salmo gairdneri Richardson

Abstract. Electron microscopical observations of skin of rainbow trout revealed the presence of several types of phagocytic cells in the epidermis, most notably macrophages, some of which were seen crossing the basal lamina. Occasionally, filament-containing cells showed either melanin granules or phagosomes, suggesting these cells were also capable of phagocytosis. No cells with the characteristics of the Langerhans cells were observed, which does not necessarily preclude the possibility of macrophages being able to play an identical role as antigen-trapping cells.     

Circulatory and ionoregulatory effects of atrial natriuretic peptide on rainbow trout (Salmo gairdneri Richardson) fed normal or high levels of dietary salt

Rainbow trout fed a normal salt diet (1.3% NaCl) or a high salt diet (12% NaCl for at least 6 months) were chronically cannulated in the dorsal aorta and received 10 μg kg⁻¹ ANP (1–28 human, UBC-Bioproducts) infused over a 10 min period. This had an insignificant influence on sodium balance, blood electrolytes and branchial sodium fluxes. In fish given a normal diet, the blood pressure and heart rate were uninfluenced by ANP, but pulse pressure was reduced by on average 60% and in some cases was not evident at all. Blood pressure in the fish fed a high salt diet was significantly higher than in the control fish; this together with heart rate and pulse pressure was not affected by ANP administration.     

Characterization of angiotensin-converting enzyme in the gills of rainbow trout,Salmo gairdneri (Richardson)

Several physical and chemical parameters of angiotensin-converting enzyme (ACE) were determined using a spectrophotometric assay of gill tissue homogenates from rainbow trout. This assay is based on the evolution of free hippuric acid via enzymatic cleavage of histidyl-leucine from the synthetic substrate hippuryl-l-histidyl-l-leucine (HHL). Piscine ACE exhibited enzymatic and kinetic properties similar to those reported for the partially purified mammalian enzyme. Proteolytic activity was both temperature and pH dependent and demonstrated hyperbolic kinetics with an apparent Km of 2.5 mM. Hydrolysis of HHL was activated by Cl^– at concentrations between 20 mM and 100 mM. Captopril (1 × 10^–6 M) and MK-422 (1 × 10^–6 M) blocked trout gill ACE activity, however, EDTA was inhibitory only at high concentrations (1 × 10^–3 M). These results demonstrate that trout ACE is functionally similar to mammalian ACE and that the spectro-photometric assay for ACE developed by Cushman and Cheung can be applied to analysis of converting enzyme activity in fish tissue homogenates.     

Secondary response of rainbow trout (Salmo gairdneri Richardson) to DNP-haemocyanin and Yersinia ruckeri

Yearling rainbow trout were immunized by intraperitoneal injection of 1 mg dinitrophenol-keyhole limpet haemocyanin (DNP-KLH) or 10⁹ formalin-inactivated Yersinia ruckeri. Fish were regularly bled to establish individual kinetics by passive haemagglutination and agglutination, respectively. Groups of 20 to 30 fish were used. A control group was also provided which received its first injection simultaneously with the booster injection for the experimental group. The secondary anti-DNP response was never found to be enhanced when compared with the primary one but, in contrast, a noticeable secondary response was observed with the bacterial antigen.     

The effect of water-borne magnesium on the dietary magnesium requirement of the rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) (mean initial weight 0.84 g) were fed diets containing graded levels of magnesium (Mg) (78 to 725µg/g) while being exposed to one of several levels in the rearing water (1.4 to 1000 mg/l). Uptake of Mg from the water, in Mg-deficient fish, was linearly related to the water Mg concentrated. It appears that the fish's Mg requirement can be met from either or both the diet or water. Under the experimental conditions, a water-borne concentration of 46 mg/l was calculated to be sufficient to meet the Mg requirement of the fish fed a Mg-free diet.     

The toxicity of the cyanobacterium Microcystis aeruginosa to rainbow trout, Salmo gairdneri Richardson

Abstract. Microcystis aeruginosa is a common cyanobacterium of nutrient-rich fresh waters. It has been implicated in a large number of poisoning incidents involving wild and domesticated terrestrial animals. The study showed that a pure strain of M. aeruginosa toxic to mice was non-toxic to rainbow trout immersed in a culture for 10 days. In contrast, when presented by intraperitoneal injections Microcystis caused an acute toxic response with 100% mortality of fish within 36 h. The histopathology of the response is described and contrasted with that to another cyanobacterium, Anabaena cylindrica , which was shown to be non-toxic by immersion or injection.     

Relationship between transmembrane potential and activation of motility in rainbow trout (Salmo gairdneri)

A hypothesis is developed that activation of motility in rainbow trout spermatozoa is a result of membrane hyperpolarization. This hypothesis was developed to explain experimental observations of a relationship between membrane potential and motility as revealed by the use of voltage sensitive fluorescent dyes. The results lead to the following conclusions: a) Transmembrane potential hyperpolarizes with decreasing KCl concentration in 100 mM NaCl. b) Transmembrane potential hyperpolarizes with decreasing NaCl concentration. c) NaCl is three time less effective in changing transmembrane potential and two orders of magnitude less effective in inhibiting activation of motility than KCl. d) Chloride ions have little effect on transmembrane potential or motility. e) Increases in osmotic pressure with the non-ionic molecule sucrose increased the amount of KCl required to inhibit activation. f) The major effect of Na⁺ on K⁺ inhibition may be osmotic.It is suggested that while sperm cells are in the seminal plasma in the reproductive tract of the male rainbow trout their transmembrane potential is maintained above an activation threshold, probably through Na/K pumps which are found in almost all animal cells. Since K⁺ is the most important ion in determining the transmembrane potential, hyperpolarization of the plasma membrane below an activation threshold occurs when the sperm cells are diluted, during spawning, into the low K⁺ environment of freshwater.