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.     

Influence of bovine growth hormone on the growth dynamics of mosaic muscle in relation to somatic growth of rainbow trout, Salmo gairdneri Richardson

Bovine growth hormone (bGH), administered intramuscularly at 20 μg^-1 every 2 weeks, produced faster somatic growth in rainbow trout fingerlings to approximately 30 cm than in those not receiving the hormone. Both groups were maintained at 12° C, with a photoperiod of 16 : 8 LD, and on ad libitum rations daily. The faster growth was characterized by a controlled increase in input of fibres into the mosaic muscle (which dominates the body tissues by its bulk). It is not known if the enhanced input of fibres is an example of the known ability of the mosaic fibre mass to respond with flexibility and precision to widely differing somatic growth rates, or is a specific consequence of the growth hormone. In other fingerling trout receiving 4-5% daily rations and consequently growing slowly, bGH did not stimulate growth or evidently modify fibre input dynamics. Body dry weight, and condition ( K ), though modified by rations and growth rate, evidently had little effect on muscle fibre growth.     

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.     

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.     

Enzyme activities of plasma and selected tissues in rainbow trout Salmo gairdneri Richardson

This paper describes the determination in rainbow trout of the normal levels in the plasma of eight enzymes known to be significant in animal pathology. Some relationships between plasma enzyme levels and the enzyme activities in selected tissues are discussed. For LDH which is ubiquitously distributed, we chose, by way of saturation tests, the optimum concentrations of pyruvate and NADH in the assay medium. The LDH 'isoenzyme ratio' was determined for heart tissue, liver, and white muscle. When blood was withdrawn from caudal vessels, we observed a net increase of plasma enzyme activities, mainly of CPK and LDH, which was demonstrated to originate from surrounding muscle. Thus cardiac sampling was the only suitable way of obtaining blood for this kind of study. Slightly haemolyzed blood appeared suitable for enzyme determinations except for Alk Pase which is about 50 times more concentrated in erythrocytes than in plasma. CPK was highly concentrated in the heart and the muscle, GOT was concentrated in the heart while the liver appeared to be a valuable source of GDH (as well as the kidney) and GPT.     

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.     

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.     

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.     

Effects of implanted dummy transmitters on mortality, growth and tissue reaction in rainbow trout, Salmo gairdneri Richardson

For the first time, workers in the U.K. with a Home Office licence may surgically implant transmitters into wild fish in order to track them. A laboratory study was designed to investigate the effects of intraperitoneally implanted transmitters on rainbow trout. No significant difference in mortality or growth occurred between control, sham-implanted and implanted groups of fish over a 7-month period. Transmitters became encapsulated by connective tissue, the composition of which is described. Three fish expelled transmitters via the body wall without subsequent mortality or morbidity. Histological evidence suggests pressure necrosis of the body wall adjacent to the tag to be the mechanism of expulsion. With good surgical procedure, intraperitoneal implantation appears to provide a suitable technique for attaching transmitters to fish, and may be preferable to existing methods for many fish.     

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.     

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.     

Effects of sampling conditions on selected blood variables of rainbow trout, Salmo gairdneri Richardson

The effects of two methods of specimen immobilization (MS 222 anaesthesia and stunning), two types of anticoagulant (EDTA and heparin), two storage temperature ranges (0–2°C and 22–25°C) and four sample storage periods (0, 1, 3, and 24 h) on the haemoglobin, haematocrit, plasma and packed cell sodium, potassium and chloride ion concentrations and packed cell ATP levels of rainbow trout were examined. Stored samples exhibited increases in cell volume, net transfer of sodium and chloride from plasma into cells, net loss of potassium to plasma and rapid depletion of ATP. Room temperature conditions and prolonged storage exacerbated these changes. Use of EDTA, particularly in combination with MS 222, frequently led to haemolysis. Least change in most variables was observed in samples drawn from stunned specimens, treated with heparin and refrigerated before use or preparation for deep cold storage.     

Relative growth of tissues at different somatic growth rates in rainbow trout Salmo gairdneri Richardson

Growth of tissues (heart, spleen, liver, gonad, gut, skin, visceral fat and carcase) in immature rainbow trout relative to growth of whole fish, was examined by means of allometric analysis (y=ax^b; Huxley, 1932) of wet and dry weights. Relative growth rates of tissues are compared in an initial sample of fingerlings (< 11·29 g), and in fish (> 11·29 g) growing rapidly (at 12°C ad libitum rations) and slowly (at 12°C, 4–5% rations, and 7°C ad libitum rations). In the fingerlings of the initial sample, the major tissues by weight (liver, gut, skin, visceral fat) increased relatively more rapidly than whole body weight (i.e. with positive allometry; b> 1·00), and carcase increased more slowly than body weight (b< 1·00). Above fingerling size, the reverse holds: tissues other than carcase (with exception of visceral fat) increased less rapidly than body weight (b < 1·00), and carcase more rapidly (b > 1·00). These principles hold for post-fingerling, immature rainbow trout, regardless of growth rate differences of whole fish, and even in fish that also received bGH (bovine growth hormone). The characteristic b (slope) values in the allometry equations for the wet and dry weights of the various tissues tend to remain constant, despite whole fish growth rate differences and the effects of this constancy are to maintain approximate constancy of body proportional (%) wet and dry weights. It is emphasized however that the effect of b values only slightly > or < 1·00 can cause important changes in the proportional (%) weights of major tissues as fish continue to increase in size. In low (4–5%) rations fish (without bGH) the slope (b) value for gut is less than for fish on ad libitum rations with the result that gut proportional weight is significantly less among these fish. In fish on ad libitum rations at 7°C, the slope (b) value for skin is greater than for all other (12°C) groups; skin proportional weight for the 7°C group is therefore, significantly greater. The overall impression of relative growth in immature rainbow trout is of remarkable conservativeness of body proportional weights regardless of overall somatic growth rate.     

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.     

Effects of malachite green on leucocyte abundance in rainbow trout, Salmo gairdneri (Richardson)

Blood counts from more than 1000 young-of-the-year rainbow trout, Salmo gairdneri (Richardson), were examined to determine if static exposure to malachite green at 1·35,13·5, or 21·0 mg/1 for 25–30 min or 42·0 or 72·0 mg/1 for 5 min caused chronic leucopaenia. The major changes in fish exposed for 25–30 min came during the first 24 h. After an initial lag of 3·4 h, total leucocyte-thrombocyte counts in both treated and control fish rapidly declined. Recovery was essentially complete 1·4 days after exposure, and no leucopaenia was noted after 14 or 28 days. Thrombocytosis developed during the first 24 h in fish exposed to the higher concentrations. Lymphopaenia and neutrophilia also developed, but abated after the 4th post-treatment day. Leucocyte numbers in control and exposed groups were virtually the same by the 14th day. The total leucocyte-thrombocyte counts in fish exposed for 5 min declined after 24 h, but counts were not as depressed as those in fish exposed for 30 min.
Because leucocyte changes similar to those in exposed fish were evident in the controls in both experiments, we believe that the leucocyte changes in rainbow trout exposed to malachite green were a result of a nonspecific vertebrate stress syndrome, rather than of specific leucocytotoxic effect of this chemical.     

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.     

Effects of temperature, salinity, and feeding on aminotransferase activity in the liver and white muscle of rainbow trout (Salmo gairdneri Richardson).

1. The liver-somatic index of rainbow trout is governed by temperature and salinity, and by the interaction of these two factors. 2. The overall liver-alanine aminotransferase activity (in units/100 g body weight) increases slightly with increasing salinity of the surroundings in the case of rainbow trout. 3. The overall liver-aspartate aminotransferase activity (in units/100 g body weight) in rainbow trout depends on their food and the temperature at which they are kept. 4. Salinity adaptation leads to reductions in the specific alanine and aspartate aminotransferase activity in the liver of rainbow trout. 5. The specific alanine aminotransferase activity in the muscle of starving rainbow trout kept in diluted seawater (580 mOsm/l, 18 degrees C) is clearly higher than in control animals kept in tapwater.     

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.     

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.