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.     

Compensatory growth in the rainbow trout, Salmo gairdneri Richardson

The effect of a period of starvation and subsequent refeeding on the weight and length of rainbow trout at different times of the year has been investigated. Fish that have been starved for 3 weeks and then fed for 3 weeks show a weight gain equivalent to or greater than that of fish fed normally for the 6 week period, in four out of the five periods studied. The study provided evidence of the adaptation of the fish to starvation followed by what may be termed compensatory growth once feeding was resumed. The length changes of the fish indicate that the weight gains were due to growth rather than increases in gut fat deposits or increased water uptake.     

The palatability of amino acids and related compounds to rainbow trout, Salmo gairdneri Richardson

Using a behavioural assay, the palatability of urea, taurine, betaine and the 20 common amino acids (L-isomers) to rainbow trout was determined. The trout responded positively only to aqueous solutions of leucine, isoleucine, proline, phenylalanine, tryptophan, methionine, glutamate, arginine, taurine and urea. Proline, the most effective compound, was active at 10 ^-4 m but not 10^-5m. Palatibility was not directly related to test solution pH; concentration and molecular structure apparently played a greater role. There is good, though not perfect, agreement between the behavioural results obtained here and published electrophysiological data on the palatal sensitivity of rainbow trout to these substances.     

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 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.     

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.     

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.     

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.     

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.     

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.     

Effects of copper on branchial ionoregulation in the rainbow trout,Salmo gairdneri Richardson

Summary Hard- and softwater acclimated adult rainbow trout were statically exposed to copper (12.5, 25, 50, 100, and 200 ppb) for two, 12 h periods at neutral and pH 5.0. Unidirectional Na⁺, and Cl⁻, and net Na⁺, Cl⁻, K⁺, and ammonia fluxes were monitored as a measure of branchial ionoregulatory disturbance. Copper concentrations as low as 12.5 ppb led to measurable ion losses. Net Na⁺, Cl⁻, and K⁺ losses were concentration dependent and unaffected by prior acclimation to either hard- or softwater at both neutral pH and pH 5. From 12.5 to 50 ppb net NaCl losses arose primarily as a result of the inhibition ofJ _in, and at higher concentrations,J _out was also stimulated. In softwater,J _in was more resistant to inhibition than in hardwater. However, in hardwater,J _out recovered to normal levels during the second 12 h period, but no such recovery was found in softwater. Plasma NaCl was inversely correlated with [copper], while plasma glucose and ammonia increased with [copper]. At pH 5.0 and [copper] from 12.5 to 50 ppb, H⁺ contributed significantly to the total ion loss, while at 100 and 200 ppb, ion losses were no greater at pH 5.0 than at neutral pH. In no case were the effects of copper and H⁺ strictly additive.     

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.     

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.     

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.     

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.     

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.     

The influence of photoperiod on sexual development in underyearling rainbow trout, Salmo gairdneri Richardson

Photoperiods of 19 h light or more induced sexual maturation in male underyearling rainbow trout but did not influence maturation in the females. Early maturation was not a consequence of the increased growth under long photoperiods. The rate of mortality was much higher in the early maturing males than in the immature fish.