Accessory cells in the gill epithelium of the freshwater rainbow trout Salmo gairdneri

Two types of mitochondria-rich cells were identified in the gill epithelium of the freshwater-adapted rainbow trout, Salmo gairdneri, after selective impregnation of their tubular system with reduced osmium. A first type consisted of large cells with a poorly developed and loosely anastomosed tubular system; thus, that resembled the chloride cells commonly encountered in the gill epithelium of freshwater-adapted euryhaline fishes. A second type comprised smaller cells with an extensively developed and tightly anastomosed tubular system. These never reached the basal lamina of the gill epithelium and were adjacent to chloride cells, to which they were linked by shallow apical junctions (100-200 nm); thus, they resembled accessory cells, which are currently found in the gill epithelium of seawater-adapted fishes but are usually lacking in freshwater living fishes. Transfer of the freshwater-adapted trout into seawater induced the proliferation of the tubular system in the chloride cells and the formation of lateral plasma membrane interdigitations between accessory cells and the apical portion of the chloride cells. The length of the apical junction sealing off this extended intercellular space was reduced to 20-50 nm. The tubular system of the accessory cells was not modified. The extension of the tubular system in the chloride cells of the seawater-adapted fishes indicated that, as in most euryhaline fishes, these cells have a role in the adaptation of the rainbow trout to seawater. In contrast, the function of the presumptive accessory cells in freshwater trout remains to be established.     

Sexual maturation in triploid rainbow trout, Salmo gairdneri Richardson

This paper compares some morphological and endocrinological characteristics of diploid and triploid rainbow trout.
Significant differences were found between diploid and triploid females in GSI, condition factor, gut weight, liver weight and percentage dress-out, and between diploid and triploid males in GSI, condition factor and gut weight.
Diploid females had large, well-developed ovaries containing yolk-filled secondary oocytes whereas the triploids had only string-like ovaries containing nests of oogonia. No primary oocytes were present.
All the diploid males produced copious quantities of milt but it was possible to express a thin, watery milt containing motile spermatozoa from only two of the 12 triploid males. Testes weights in triploids were similar to those of diploids but, while the diploid testes were packed with spermatozoa, those of the triploids consisted mainly of spermatocytes and spermatids with few spermatozoa present. Measurements of the heads of spermatozoa revealed that those from triploids were larger and had a wider size range than those from diploids.
Levels of testosterone and 11-ketotestosterone in triploid and diploid males were not significantly different. However, levels of testosterone and 17β-oestradiol in diploid females were considerably higher than those of triploid females.     

Plasma oestrogen levels in rainbow trout Salmo gairdneri Richardson

Levels of oestrogens in plasma of mature fall-spawning rainbow trout Salmo gairdneri were determined using a radio-immunoassay. No significant difference was found in oestrogen concentration between the sexes (male =2.5 ng/ml; female =4.4 ng/ml); between individual variability was great. Four blood samplings over a 24-h period via cardiac puncture of males revealed no diel variation or change in estrogen levels due to the stress of bleedings. Although no gonado-somatic index-estrogen relationship could be demonstrated for either sex, there was correlation between oestrogen and androgen levels in the female.     

The saccus dorsalis of the rainbow trout,Salmo gairdneri Richardson

The saccus dorsalis of the brain of the rainbow trout, Salmo gairdneri Richardson, has been investigated by means of histological, cytochemical, enzyme-cytochemical, electron microscopical autoradiographical techniques. The saccus dorsalis is a rostro-dorsal evagination of the diencephalic roof, and consists of a partly folded epithelial wall separating the cerebrospinal fluid from the meningeal matrix fluid. The well-developed vascular system around the epithelial wall, consisting of capillaries with different diameters, seems to be part of the pineal vascular system. No structures were found that may be involved in a possible mechanical or nervous blood flow control. The single-layered epithelium consists of highly specialized cells of one specific type. These cells are mainly characterized by infolded basal membranes, long microvilli of a peculiar shape, non-folded lateral membranes bordering intercellular spaces, apical concentrations of elongate and cup-shaped macromitochondria, a basally located rough endoplasmic reticulum, an apically situated smooth endoplasmic reticulum and apical concentrations of micropinocytotic vesicles. Morphological evidence is presented of a multiple function of these cells: (1) fluid secretion, (2) extrusion of low molecular weight organic substances into the ventricular system, (3) uptake of high molecular weight substances, and (4) uptake of low molecular weight organic substances (aminergic neurotransmitters [GABA]) from the cerebrospinal fluid. The significance of light and dark cells is discussed. Indications of a possible innervation of the saccus dorsalis epithelial cells were not observed. The functional significance of the saccus dorsalis (possible analogue of the choroid plexus?) is discussed.     

Glucose transport across the gill of the rainbow trout, Salmo gairdneri

Glucose fluxes across the gills were measured in freshwater-adapted trout (Salmo gairdneri) using an in vitro, perfused-head preparation. A large asymmetry was observed for the primary lamellar pathway, glucose permeability in the serosa-to-mucosa direction being up to 24 times greater than the permeability in the mucosa-to-serosa direction. Chloride cells appeared to possess a maximal rate of transport, or TMG, of 79 mumol/hr per 100 g. Phlorizin, phloretin and, to a lesser extent, harmaline caused an increase in the rate of glucose efflux. The results suggest that the tubulo-vesicular reticulum, into which plasma is introduced under low pressure, may be regarded as a reabsorption site for glucose in a way similar to the nephron proximal tubule. Thus, essential molecules such as glucose are removed while excess or non-essential substances are excreted into the external medium.     

Development of photobehavioural responses in young rainbow trout, Salmo gairdneri Richardson

The photobehaviour of young rainbow trout was studied from the time of hatching to completed emergence using an artificial turf substrate incubation system. At all light energies tested, free-embryos initiated a substantial downward movement and rates of fish descent did not appear to reflect the order of light energy levels. A nocturnal activity rhythm was established early in the downward phase. The occurrence of a rapid photoresponse shift 21 days after hatching coincided with the synchronous onset of emergence in all fish groups and the depletion of 85% (by volume) of the yolk reserve. Concurrent morphological observations indicated that the photoresponse change occurred when fish were about 25 mm long, and when paired and median fins were fully developed.     

Chromosome polymorphism in the rainbow trout (Salmo gairdneri Richardson)

Chromosome preparations from lymphocyte cultures of 50 rainbow trout were studied. Diploid chromosome numbers of 59, 60, 61, 62 and 63 were found in different individuals in which the arm number (NF) was 104. Intraindividual polymorphism was found at a low level in 25 of the fish. The results suggest that numerous chromosome polymorphisms exist in rainbow trout.     

The gill sialic acid content as an index of environmental stress in rainbow trout, Salmo gairdneri, Richardson

The gill sialic acid content in Rainbow Trout exposed to several aqueous concentrations of ammonia NH₃ and/or to a high environmental pH was determined by two different methods. The results showed Warren's method was adequate for the biological material, even without purification of the extracts by Dowex 2.8 resin. A significant increase of the sialic acid concentration occurred in fish exposed to ammonia.     

Esterases and phosphatases in the leucocytes of rainbow trout, Salmo gairdneri Richardson

A preliminary report is made on the distribution of acid phosphatases and acid esterases in the cells of rainbow trout. A modified technique for the cytochemical demonstration of acid esterases is given, resulting in clearer visualization. Lymphocytes undergoing transformation in the presence of phytohaemagglutinin show a parallel decrease in enzyme localization for acid esterase and acid phosphatase as transformation in culture proceeds.     

Polyploidy induced by hydrostatic pressure in rainbow trout, Salmo gairdneri Richardson

Triploid rainbow trout were produced by hydrostatic pressure applied to eggs 40 min after fertilization. Treatment for 10 min with or without exposure to 2% ether produced high hatching rates. Nuclear measurements from serial section of 40-day-old fry and from blood smears of 5-month-old juveniles showed that the proportion of triploid individuals was 80–90%. Ether treatment alone did not induce triploidy. Attempts to produce tetraploids by hydrostatic pressure treatment of eggs at 8 h after fertilization failed. Parallel results were also obtained with heat shock.     

Enzyme-cytochemistry of the saccus dorsalis of the rainbow trout,Salmo gairdneri Richardson

Summary In the saccus dorsalis of the rainbow trout, Salmo gairdneri Richardson, the activity of various enzymes (transferase, lyases, oxidoreductases, hydrolases) have been studied in detail.The results of this enzyme-cytochemical study firmly demonstrate that the organ is metabolically highly active. The epithelial cells have a strong energy metabolism. Energy production can take place under aerobic as well as under anaerobic conditions. Evidence is presented that glucose from blood is directly utilized for energy demands. The epithelial cells show also high synthetic activities. The moderate amino acid metabolism may participate in the synthesis of an acid mucopolysaccharide-protein complex, especially in the so-called dark cells. Lipid metabolism appears to be restricted to the mitochondria, indicating a high turnover of lipid moieties in the membranes. In contrast to the normal looking mitochondria, the macromitochondria — besides shape and localization — have an extremely high lipid and monoamine metabolism, which may point to a special function in the cellular economy. The high activity of enzymes involved in the degradation of monoamines and in the hydration of CO₂ is of particular physiological interest. The significance of the observations is discussed in relation to formerly obtained indications on the involvement of the saccus dorsalis in fluid secretion, extrusion of organic substances of low molecular weight into the ventricular system and uptake of organic substances from the cerebrospinal fluid.The hypothesis of the saccus dorsalis being an analogue of the choroid plexus is supported by several relevant data.     

Exercise training and the stress response in rainbow trout, Salmo gairdneri Richardson

Plasma levels of catecholamines, cortisol, and glucose were monitored in rainbow trout during a 6-week forced swimming exercise programme. Compared to resting non-exercised controls, resting trained fish had lower levels of epinephrine, norephinephrine, cortisol, and glucose during the last 3 weeks of training. Initially, trained fish that were swimming had higher levels of epinephrine than resting trained fish. After 2 weeks of exercise, swimming did not significantly elevate epinephrine levels in trained fish. Glucose levels were consistently greater in swimming fish than in resting fish. At the end of the training period, exercised trout had lower (15–20%) oxygen consumption rates while resting or swimming than unexercised fish.
After a 5-month forced swimming exercise programme plasma levels of catecholamines and glucose were monitored in trained and untrained cannulated rainbow trout after 2 min of mild agitation. Trained fish showed an immediate (within 1 min) increase in the levels of epinephrine, but not norepinephrine and a delayed (within 15 min) increase in the levels of plasma glucose. Epinephrine levels returned to pre-stress levels within 15 min. Untrained fish had no significant increase in the plasma levels of norepinephrine, epinephrine, or glucose.     

Some aspects of sustained training of rainbow trout, Salmo gairdneri Richardson

Groups of 6-7 cm length rainbow trout, Salmo gairdneri Richardson, were simultaneously trained at four water velocities (0, 1·4, 2·2 and 3·5 Ls^-1) for a period of 46 days. Oxygen consumption and swimming ability (fatigue time) were then measured. Only training at 3·5 Ls^-1 increased the swimming ability of the fish. A study of the relative proportion of the white and red muscles indicated that the white muscle was increasing its mass at velocities in excess of 2·2 Ls^-1. The oxygen consumption rate of the trained fish was lower than that of the untrained fish when considered over the whole velocity range.     

The structure of the gill of the trout,Salmo gairdneri (Richardson)

Summary A light and electron microscopic study was made of the structure of the gill arch, filament and secondary lamella of Salmo gairdneri R. Blood pathways through the gill were traced from serial histological sections, and from the examination of ink perfused tissue and perspex casts formed following resin injection of the circulatory system.The epithelium covering the gill consists of unspecialized, dark, chloride and mucous cells. The distribution of specialized cells appears to be related to gill function. The basement membrane underlying the epithelium consists of three layers, the inner collagen layer being continuous with the connective tissue core of the gills.Blood supply to the secondary lamellar respiratory surface is via branchial, filament and secondary lamellar arteries. Blood spaces of the secondary lamellae are delimited by pillar cells containing what appears to be contractile material. The marginal channel of each lamella is bounded distally by cells of endothelial origin. A network of lymph spaces within the filaments connects with efferent branchial arteries. Nutritionary capillaries within the filaments connect with afferent branchial arteries. No shunts between afferent and efferent filament arteries were found.Data from this study and previous physiological and histopathological studies suggest a mechanism for the control of blood flow to suit the respiratory requirements of the fish. This mechanism involves a system of recruitment of additional respiratory units and changes in overall blood flow patterns.This work formed part of a thesis submitted for the degree of Doctor of Philosophy in 1971 and for which M. M. was in receipt of a studentship from the Natural Environmental Research Council. The authors are grateful for the support given by research grants from the M.R.C (P.T.) and the N.E.R.C. (M.M.), and to Prof. G. M. Hughes in whose department the work was carried out.     

The haematological assessment of bacterial infection in rainbow trout, Salmo gairdneri Richardson

The pH, pCO2 and pO2 values for diseased fish did not differ significantly from those values for healthy fish, but fish treated with terramycin showed a highly significant rise in pCO2 with a corresponding fall in pO2. Haematocrit values, as well as haemoglobin and total plasma protein concentrations were significantly lower in diseased fish while treated fish showed a significant rise in total plasma protein. Glucose concentrations fell very significantly in diseased fish and showed a significant increase in treated fish.
The plasma electrolytes, sodium, potassium and chloride, were significantly reduced in diseased fish and potassium levels also fell in treated fish. Diseased fish showed very significantly reduced erythrocyte counts. Of the three parameters MCV, MCH and MCHC, only the values for MCH in diseased fish differed significantly from those for healthy fish.     

Ultrastructure of the liver of the fingerling rainbow trout Salmo gairdneri Richardson

Portions of the livers of fingerling rainbow trout were studied by light and electron microscopy. The histology, cytology and ultrastructure of mesothelial cells, serosal fibroblasts, hepatocytes, sinusoidal endothelial cells, endothelial cells of central veins and blood cells were described. Mesothelial cells and fibroblasts constituted a very thin capsule. Hepatocytes contained extensive areas of rough surfaced endoplasmic reticulum, consisting mainly of parallel cisternae and pools of glycogen. One or two nuclei and numerous mitochondria occurred in the areas of endoplasmic reticulum, but never in the pools of glycogen. Hepatocyte surface possibilities included hepatocyte to hepatocyte, hepatocyte to bile canaliculus, hepatocyte to space of Disse and hepatocyte to serosa. The trout liver was compared compared to channel catfish liver and to rat liver. Functional implications of the structural features were discussed.     

Observations of rainbow trout, Salmo gairdneri Richardson, infected with Cryptobia salmostica

Rainbow trout, Salmo gairdneri , were experimentally infected with Cryptobia salmositica . The parasitaemia was associated with increases in the size of the spleen, liver and heart (% body weight). The splenomegaly was pronounced and was often 600-fold larger. The amounts of blood lactic acid and lactic dehydrogenase in the infected and control fish were similar. However, glycogen levels of the liver, heart and epaxial muscle declined. Liver glycogen levels were most affected and decreased to values which represented 20% of the control values. The pattern of the glycogen levels of the liver, heart and epaxial muscle declined to rise to normal values by day 56 post-inoculation. Thus, the glycogen levels both paralleled the acute parasitaemia and the subsequent partial recovery of the infected fish as they tolerated a low chronic parasitaemia.     

Effects of sampling on blood parameters in the rainbow trout, Salmo gairdneri Richardson

The effects of sampling and short-term storage of blood samples on the blood parameters of rainbow trout were evaluated by comparing values obtained from resting fish sampled via cannulae and from fish sampled by cardiac puncture. Sampling stress causes an increase in haematocrit value and a decrease in mean cellular haemoglobin concentration, indicating red cell swelling. These changes are aggravated by consecutive storage of samples. Also, blood ionic balance is affected. The K⁺ concentration of plasma increases and plasma Cl⁻ concentration decreases owing to sampling. During storage the plasma K⁺ concentration decreases far below resting levels in samples taken by cardiac puncture, whereas plasma Cl⁻ level returns to pre-stress levels. Owing to the sampling- and storage-induced changes in blood parameters, care must be taken to ensure that similar sampling procedure is employed throughout to allow reliable comparisons between groups to be made.