Effects of salinity and starvation on the alimentary canal anatomy of the rainbow trout Salmo gairdneri Richardson

A study has been made of the effects of salinity, starvation and salinity-starvation interactions on the structure of the alimentary canal of immature rainbow trout Salmo gairdneri Richardson. Intestinal and rectal cross-sectional areas and the height of the intestinal villi increased with salinity. The thickness of none of the tissue layers measured in the intestine and rectum, including the columnar epithelium and the tunica propria, was influenced by salinity. There was a significant negative correlation between salinity and mucous cell distribution density in both the intestine and rectum. In trout acclimatised to salinities of 15.0 p.p.t. (parts per thousand) and above, there was a high incidence of deep depressions in the columnar epithelium. The oesophagus and stomach were not visibly affected by salinity.
There was a marked decrease in intestinal and rectal cross-sectional area and height of intestinal villi with starvation except in 32.5 p.p.t. sea water. Mean intestine epithelial cell height decreased with starvation at 32.5 p.p.t. A 48 day period of starvation had little effect on the posterior oesophagus and the cardiac stomach.     

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.     

Recovery growth following periods of restricted rations and starvation in rainbow trout Salmo gairdneri Richardson

Fingerling rainbow trout (6.9 to 11.6 cm fork length) maintained at 12° C were either: fed restricted rations (3% of dry body weight/day) for 16 weeks, or starved for 3 weeks (14.5% weight loss), or for 13 weeks (32.5% weight loss). Whole body wet weights and dry weights (as % of wet weight), and wet and dry weights of tissues (heart, spleen, liver, skin, gonad, gut, visceral fat, and 'carcase') resulting from these treatments were compared to corresponding weights of an 'initial sample'. Visceral fat was completely utilized during both short and long-term starvation and gut was significantly reduced in the extended starvation group.
During subsequent recovery growth on full rations, following food deprivation, fish grew at approximately the same rate as fully-fed controls, which had not suffered food deprivation, as regards body wet weight and condition ( K ), but tended to surpass controls in % dry weight.
Heart, liver, gonad, gut and visceral fat also increased during recovery growth in a manner suggestive of overcompensation in response to former food deprivation. Gut, skin and carcase dry weights were less in the control, and in the 14.5% weight loss groups following recovery growth than in those in 3% rations and in the severely starved group, indicating that the effects of slow growth resulting from limited rations resemble those of severe starvation more than those of limited starvation.     

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.     

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 effects of starvation upon protein turnover in red and white myotomal muscle of rainbow trout, Salmo gairdneri Richardson

Protein synthesis rates of both red and white muscle were measured using a constant infusion technique in fed and starved rainbow trout over a period of 2 months. In both tissues, rates of protein synthesis fell during starvation although the fall was more rapid in white than in red muscle. The reduced rates of protein synthesis were correlated to a reduced level of RNA in the tissues and a lower rate of translation of the RNA present. Estimated rates for protein degradation in white muscle showed a marked initial increase but with more prolonged starvation the degradation rate become only slightly greater than that in the fed fish.     

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.     

Cadmium exposure of rainbow trout, Salmo gairdneri Richardson: effects on immune functions

Differential leucocyte counts, phagocytosis, humoral antibody response and the in vitro blasto-genetic response to mitogens (lipopolysaccharide and Concanavalin A) and to an antigen ( Vibrio anguillarum ) were studied in rainbow trout exposed to 0,0.7 or 3.6 μg Cd 1⁻¹ for 12 weeks.
Although the fish did not exhibit any clinical or histological changes, cadmium exposure was found to affect two of the immune parameters measured. The cellular response of fish immunized with V. anguillarum to the homologous antigen was significantly lower for splenocytes obtained from fish exposed to cadmium for 9 weeks (3.6 μg Cd 1⁻¹ group) than for splenocytes obtained from non-exposed fish. Conversely, the humoral antibody response to V. anguillarum O-antigen was higher in the 3.6 μg Cd 1⁻¹ group than in the non-exposed group. Protective immunity of fish vaccinated against V. anguillarum was equally as good in the cadmium-exposed group as in the non-exposed group. No cadmium-induced changes in differential leucocyte counts or in the proportions of phagocytic cells were observed.     

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 effects of external ultrasonic tagging on the swimming performance of rainbow trout, Salmo gairdneri Richardson

The effects of externally mounted ultrasonic tags on the tail beat frequency (TBF) and opercular beat rate (OBR) of rainbow trout was measured at different swimming speeds. The increase in relative drag caused by the tags was also measured. Two tag types were used: one where both the circuitry and the battery were in a single package mounted on one side of the fish, the other where they were in two packages mounted symmetrically on either side of the fish. Both tag types raised both TBF and OBR. Of the two, the symmetrical tag effects behaviour less, especially at low swimming speeds, even though it causes a greater increase in relative drag.     

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.     

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.     

Some effects of exposing rainbow trout (Salmo gairdneri Richardson) to phenol solutions

Phenol (C₆H₅OH) at non-lethal concentrations in hard water had no effect on the urine flow rate or haematocrit of rainbow trout for exposure times of 24 h. Phenol was detected in the urine in a non-conjugated form and unchanged phenol was also extracted from muscle, blood and brain. Uptake of phenol into tissue was found to be rapid with an equilibrium concentration being reached in 3 h. Loss of phenol after exposure was as rapid. The equilibrium concentration for muscle was similar to the phenol concentration to which the fish were exposed. Blood and brain contained smaller amounts. Close to or above the lethal threshold concentration (48-h lc₅₀9 mg 1^-l; 15°C) the fish had higher than ambient concentrations in their tissues most notably in the brain. Above the lethal threshold there is evidence of a large uptake of phenol by erythrocytes.     

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

Fifty rainbow trout of the Kamloops strain were examined for 12 haematological parameters: erythrocyte sedimentation rate, haemoglobin, packed cell volume, erythrocyte count, erythrocyte diameters, mean cell volume, mean cell haemoglobin, mean cell haemoglobin concentration, leukocyte count, differential leukocyte count, plasma total protein and plasma glucose concentration. The fish had been held under known environmental and dietetic conditions, and at the time of sampling were 14 months old. The majority of results for erythrocyte sedimentation rate, haemoglobin, packed cell volume, erythrocyte count, erythrocyte diameters, total protein and differential leukocyte count fell within narrow ranges. The total leukocyte counts and glucose levels were more widely spread. The results are discussed and compared with those already published for Idaho and Shasta strains. It is impossible to say whether the differences that were observed between Kamloops and these other varieties were due to strain alone, since other variables were present. Some problems associated with establishing normal ranges for these parameters in fish are discussed.     

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.     

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.     

Lipid mobilization during starvation in the rainbow trout, Salmo gairdneri Richardson, with attention to fatty acids

Rainbow trout, Salmo gairdneri , were fed pelleted food ad libitum for 35 and 50 days. Lipid deposits were determined in the viscera, liver and muscle (epaxial and hypaxial). Most of the lipid accumulated in the viscera, but the lipid content of liver and epaxial muscle also increased. Hypaxial muscle lipid content remained the same throughout the feeding period. Upon starving the fish for 27 and 48 days following 50 days of feeding, visceral lipid contributed most to energy metabolism among the depots investigated. Muscle also contributed a considerable share while the absolute amount derived from the liver was much smaller.
Patterns of fatty acid mobilization during starvation were also investigated. Saturated acids were preferentially mobilized from the viscera, resulting in a rise in the percentage of monoenes and polyunsaturates. In liver, the percentage of saturates remained relatively constant whereas the percentage of monoenes declined and polyunsaturates increased. In muscle, a substantial increase in saturates was caused by a decline in monoenes; polyunsaturate content remained constant. As a result of these shifts in relative fatty acid composition the U/S (unsaturates to saturates) ratio rose in viscera and liver and decreased in muscle. The UI (unsaturation index) responded in essentially the same way. Possible explanations for preferential fatty acid utilization are discussed in terms of energetics and structural relationships.     

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.     

Diploid gynogenesis induced by hydrostatic pressure in rainbow trout, Salmo gairdneri Richardson

Diploid gynogenetic fry of rainbow trout, Salmo gairdneri , were produced by treating eggs activated by UV-irradiated sperm with hydrostatic pressure. Treatments for l0 min at 40 min after activation with 55 000 kPa (8000 psi) pressure resulted in high hatching rates and yields of heterozygous diploid gynogenomes of up to 81%. Attempts to produce homo-zygous diploid gynogenomes by the suppression of the first mitotic division ofthe eggs failed. Ether treatment alone did not induce diploid gynogenesis.