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.     

Seasonal variations in sex steroids of female rainbow trout (Salmo gairdneri Richardson)

17β-oestradiol, testosterone, 11 -ketotestosterone and calcium were measured in plasma of female rainbow trout over the course of a single spawning season. The patterns of rise and fall of the levels of 17β-oestradiol and calcium during sexual maturation were similar to those demonstrated by other workers. Very high levels of testosterone were found in plasma of sexually mature fish—mean level 211 ng ml-1 in November and 115 ng ml-1 in January. Ovulation occurred from December to February.     

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.     

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.     

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.     

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.     

Ventilation in rainbow trout (Salmo gairdneri, Richardson) with damaged gills

An account is given of damage to the gills of trout which involved reduction in total filament length and consequently reduced respiratory surface area. It was noted that fish with the greatest gill damage tended to ventilate the gills by active swimming (ram ventilation) to a greater extent than those with more normal gills.     

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.     

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.     

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.     

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).     

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.     

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.     

Measurement of five androgens in the blood of immature and maturing male rainbow trout, Salmo gairdneri (Richardson)

Antisera for radioimmunoassay (RIA) against testosterone, 11-oxo-testosterone, 11 beta-hydroxytestosterone, 11-oxo-androstenedione, and 11 beta-hydroxyandrostenedione were raised in female rabbits. The RIAs were tested for their suitability for quantification of the steroids after thin layer chromatography of ether extracts from plasma pools of immature and maturing male rainbow trout. Results from control experiments of the RIAs (buffer blanks, sensitivity, cross reactivity, intra- and inter-assay coefficients of variation, accuracy) were all within a normal range. These RIAs should be helpful tools to test the significance of the hypothesis concerning the "interrenal-liver-gonad axis" which has been proposed to account for the high androgen levels in male trout during high reproductive activity.     

Spermiogenesis in the rainbow trout (Salmo gairdneri)

In an ultrastructural study on the spermiogenesis of the rainbow trout (Salmo gairdneri R.) four spermatogenetic stages were identified. In young round spermatids, the nuclear chromatin was first heterogeneous (euchromatin and heterochromatin). Subsequently, it became more homogeneous and started to condense in the form of coarse granules and fibers and then into fibrils associated in ribbon-like elements which eventually partly fused together. During early spermiogenesis, a juxtanuclear vacuole appeared in the area where the nuclear envelope was specialized due to condensation of material between the two envelopes and a slight accumulation of nuclear material. This area was finally located in the anterior part of spermatids and spermatozoa; it probably plays a role during fertilization. A flagellar rootlet appeared early in spermiogenesis; it may play a role in the attachment of the flagellum to the nucleus since it persisted until the centriolar complex was definitively fixed in the implantation fossa. The flagellum did not display a plasma membrane and was first located in the cytoplasm, but when it was later extruded from the cell, it acquired a membrane. The cytoplasm was rich in ribosomes (free or in small groups) but poor in membranous organelles. The few mitochondria polarized around the centriolar complex were finally organized into an annular mid-piece. The spermatids remained connected by intercellular bridges until the end of spermiogenesis. The complexity of trout spermiogenesis is intermediate between that in poecilids and that in carp and pike, which have very simple spermatozoa. The role of the material from the nucleus and the cytoplasm reaching the Sertoli cell in the control of spermatogenesis has been discussed.