Growth of five landlocked Arctic charr stocks under hatchery conditions

Growth dynamics of five stocks of Arctic charr, were compared from the fry stage in June 1986 until December 1987. Each stock originated from a different lake in Sweden: Hornavan; Näckten; Torrön; Rensjön and Visjön. Hornavan charr reached the highest final mean weight (237 g), but they were not significantly heavier than Visjön charr (206 g). Growth of fish of the three remaining stocks was similar but less rapid. The superior growth performance of Hornavan charr was most pronounced during autumn. Coefficients of variation for individual size within stocks was between 30 and 54%, with Hornavan and Näckten charr displaying least variability. Charr from Lake Visjön had a significantly lower proportion of mature males (6%) than the other stocks (19–29%) at the end of the experiment. The results demonstrate that differences in growth potential exist between stocks of charr, and these differences may be related to differential seasonal rhythms in growth. Variations in early growth, size distributions and sexual maturation seemed to be subordinate factors affecting overall growth performance.     

Growth effects in Arctic charr reared in cold water: Feed frequency, access to bottom feeding and stocking density

The effects of time restricted feeding, possibility of bottomfeeding and stocking density on the growth of Arctic charr(Salvelinus alpinus L.) were examined in fish held at lowtemperature (<2 °C). Fish fed for a restricted time (1 h) hadsignificantly (p < 0.05) lower specific growth rate (0.15 vs0.32% per day) than those fed the same ration over an extendedtime period (12 h). Increasing stocking densities had a positive andsignificant effect (p < 0.05) on growth with SGR increasing from 0.27to 0.52% per day at 2–30 kg m^-3. Fish withaccess to feed on the tank floor had a significantly higher (p <0.05) growth rate (0.3 vs 0.13% per day) than those without thepossibility to feed from the bottom. When fish were held underconditions without access to the bottom a doubling of the feed rationdid not result in a significant (p > 0.05) increase in growth rate(0.13 vs 0.12%percnt; per day).     

Glucose-stimulated lipolysis in rainbow trout,Oncorhynchus mykiss,liver

Rainbow trout, Oncorhynchus mykiss, were used to characterize further the influence of glucose on hepatic lipolysis. Liver was removed from fed fish, cut into 1 mm³ pieces and incubated for up to 5 h in Hanks medium containing either 2 mM, 5.5 mM, 10 mM, or 25 mM glucose. Glucose-stimulated lipolysis was indicated by tissue triacylglycerol (TG) lipase activity and by medium concentrations of glycerol and fatty acids (FA). Triacylglycerol lipase activity in liver pieces incubated in the presence of higher concentrations (25 mM) of glucose was significantly higher than that in liver pieces incubated in lower concentrations (2 mM) of glucose, rising from 0.075 ± 0.002 (mean ± SEM) nmol FA released/h/mg protein to 0.092 ± 0.004 units. Similarly, higher concentrations of glucose stimulated significantly more FA release and glycerol release from liver pieces than that stimulated by lower concentrations of glucose. Glycerol release from liver pieces incubated in the presence of 10 mM glucose and 25 mM glucose was ca. 2-fold to 2.8-fold, respectively, higher than that from liver pieces incubated in the presence of either 2 mM or 5.5 mM glucose. Fatty acid release from liver pieces incubated in the presence of 10 mM or 25 mM glucose was ca. 1.8-fold higher than that from liver pieces incubated in the presence of either 2 mM or 5.5 mM glucose. Notably, increased glycerol release was not accompanied by a parallel increase in FA. Fatty acid reesterification was more pronounced in liver pieces exposed to higher glucose (10 mM and 25 mM) than in liver pieces exposed to lower glucose (2 mM and 5.5 mM). ¹⁴C-incorporation studies indicated that glucose serves as a carbon source for reesterified FA in trout liver. The route of reesterification appears to be from glucose to glycerophosphate to phosphatidic acid to diacylglycerol to TG. Increasing concentrations of glucose did not affect glycerol kinase activity, indicating that glucose-stimulated lipolysis was not accompanied by increased glycerol recycling within the liver. These results suggest that glucose stimulates fatty acid reesterification and directly enhances net lipolysis in trout liver incubated in vitro.A part of this study was presented at the Annual Meeting of the American Society of Zoologists, December 26–30, 1991, Atlanta, GA.     

Growth and feed utilisation of rainbow trout subjected to changes in feed lipid concentrations

Rainbow trout Oncorhynchus mykiss grew from 44 to 326 g in 96days when held at 12 °C. Fish were fed to satiation twice dailywith either high (L₁: 30.8%, L₂:31.4%) or lower-lipid feeds (C₁: 18.8%,C₂: 21.8%). Four feeding treatments were studied.Group C₁C₂ received feed C₁ for 43 days(days 0–43) and C₂ thereafter (days 44–96).Groups L₁L₂, L₁C₂ andC₁L₂ were subjected to dietary changes asindicated by the feed designations. After a short period of feedadaptation, fish ingested similar amounts of feed energy i.e., they ateless by weight of the lipid-rich (L) feeds. Feed lipid content did notaffect growth but fish fed L-feed had reduced feed conversion ratio(FCR) compared to fish fed C-feed (0.731 vs. 0.773) during days0–43 (P < 0.01). After 96 days,L₁L₂-fish were lower in body protein(15.8%) than the C₁C₂-fish (16.8%)(P < 0.01). L-feeds also tended to increase percentage lipidand reduce percentage whole body moisture and ash. A higher net proteinutilisation (NPU) was recorded in fish fed L-feeds (43.6%)compared to fish fed C-feeds (38.8%) in days 0–43(P < 0.05). This seemed to be the result of a lower proteinintake rather than a protein-sparing effect of feed lipid. Above athreshold value of approximately 6.5 mg protein eaten·g bodywt_{minus 1}·day_–1, NPU decreased.     

Lipid-stimulated somatostatin secretion in rainbow trout,Oncorhynchus mykiss

Previous work has shown that somatostatins (SS) affect teleost lipid metabolism indirectly by inhibition of insulin (INS) and directly by stimulation of hepatic lipolysis. In the present study, rainbow trout (Oncorhynchus mykiss) were used to characterize further the lipid-SS relationship by evaluating how lipid, contributes to SS secretion bothin vivo andin vitro. In vivo hyperlipidemia was induced for up to 3 h by short-term (2 min) infusion of a triacylglycerol (TG)-rich lipid emulsion (20% Intralipid^®). Plasma total lipid concentration increased 118 and 155% over control levels 1 h and 3 h, respectively, after infusion; much of this increase was due to elevated plasma fatty acids (FA), which increased 39 and 520%, respectively, over the same time-frame. The hyperlipidemic pattern was attended by a significant increase in the plasma concentration of SS. The specific effects of fatty acids were evaluated on isolated Brockmann bodies. Palmitic acid and oleic acid stimulated SS release 378 and 82%, respectively, over baseline levels. These results indicate that lipids, and in particular fatty acids, modulate SS secretion in rainbow trout.     

Influence of feeding frequency on growth and size dispersion in Arctic charr Salvelinus alpinus (L.)

Abstract Dominance hierarchy formation in groups of fish is thought to be a major reason for the development of size heterogeneity. The objective of the current experiment was to examine the influence of different feeding frequencies on growth and changes in size distribution in groups of Arctic charr Salvelinus alpinus (L.). The fish were fed equivalent excess rations continuously for 24 h a day, for 2 h twice a day (early morning and evening), for 2 h once a day in the morning or for 2 h once every other day also in the morning. Growth was measured by individual weighing of fish four times during the 130‐day experiment. Coefficient of variation in size within rearing groups was used to assess size dispersion and the possible development of hierarchies within the groups. Feeding frequency did not influence variation in size within groups, and there were no signs of hierarchy formation.     

Growth of rainbow trout fed a diet supplemented with earthworms,after chemical treatment

Whole frozen earthworms (Eisenia foetida) were evaluated as a partial replacement for commercial pellets for rainbow trout, Oncorhynchus mykiss. Earthworms were blanched and treated with concentrated sodium chloride (10%). Fish were submitted to four treatments: control fish were fed with a commercial diet and three groups of fish were fed with diets partially supplemented with earthworms. All fish showed the same appetite for the earthworm-supplemented diets as for the control diet during the course of the experiment (8 weeks). No significant differences (p > 0.05) were detected in the mean final body weights of all groups of fish. A significant decrease was found in the whole-carcass lipid content of fish fed diets containing 25%, 50% and 75% frozen earthworms. The results on growth rate and feed utilization efficiency of fish fed diets containing high levels of whole frozen worms suggested an adverse effect of worm incorporation, probably due to dietary energy/protein imbalance.     

Morphological, physiological and biochemical parameters characterizing the over-ripening of rainbow trout eggs

In rainbow trout (Oncorhynchus mykiss) freshly ovulated eggs and over-ripened eggs which had been retained in the coelomic cavity for 7, 14 and 21 days were investigated in aspects of morphology, physiology and biochemistry. Egg viability was significantly reduced from 85.9±16.4% in freshly ovulated eggs to 25.1±21.9% in over-ripened eggs which had been retained in the coelomic cavity for 21 days. Further during over-ripening in the ovarian fluid the pH significantly decreased, while the levels of proteins, of esterified and non esterified fatty acids and the activities of aspartate aminotransferase and acid phosphatase significantly increased. Also egg parameters changed: the wet weight of the unhardened eggs increased, the weight increase during hardening and the levels of esterified and of non esterified fatty acids significantly decreased. In freshly ovulated eggs the yolk consisted of a homogenous mass and the perivitelline space was small, but in over-ripened eggs the yolk was non homogenous with numerous vesicular inclusions and the perivitelline space was enlarged. When freshly ovulated eggs were incubated in water the cortical reaction was detectable within 5 min, in over-ripened eggs hardly no extrusion of cortical vesicles was visible and the width of the perivitelline space was very irregular.For the investigated freshly ovulated and over-ripened samples the egg viability significantly correlated with ovarian fluid parameters (pH, protein, non esterified fatty acids, esterified fatty acids, aspartate aminotransferase, acid phosphatase) and egg parameters (weight increase during hardening, weight of the hardened eggs).     

Purification and characterization of hepatic triacylglycerol lipase isolated from rainbow trout,Oncorhynchus mykiss

Trialcylglycerol (TG) lipase was isolated and partially purified from rainbow trout liver. Triacylglycerol lipase activity was assayed by measuring¹⁴C-oleic acid release from¹⁴C-triolein.¹⁴C-oleic acid release was linear for up to two hours. Optimal activity occurred at pH 7.0 and 15°C. Most of the lipase activity was recovered in the cytosolic fraction. A 27,000-fold purification was achieved after Sepharose (Bio-gel A 0.5 M, 200–400 mesh) chromatography of a resuspended 20% ammonium sulfate fraction. The molecular weight of the trout hepatic lipase as determined by size-exclusion chromatography and by SDS-polyacrylamide gel electrophoresis was 40–43 kD. Lipase-mediated hydrolysis of TG resulted in the production of diacylglycerols, monoacylglycerols, and fatty acids. Kinetic analysis indicated that V_max=0.016 nmol/h/mg protein and that K_m=0.28 mM triolein. Lipolytic activity was enhanced in the presence of cAMP/ATP-Mg²⁺. These results suggest that the liver of trout possesses a neutral TG lipase that is responsible for mobilizing stored TG and is catalytically activated by phosphorylation.A part of this work was presented at the Annual Meeting of the American Society of Zoologists, December 26–30, 1990, San Antonio, TX.     

Effect of the daily meal time on the growth of rainbow trout fed different ration levels

This study examined the effect of ration level and time of delivery of a single daily meal on the growth performance of rainbow trout held under constant water temperature and a natural photoperiod. Two similar trials were conducted, the first from March to July, 1992, using ration levels of 0.5, 1.5 and 2.5% BW d^–1 and the second from August 1992 to January 1993, using ration levels of 1.5, 2.0 and 2.5% BW d^–1.In five of the six treatment groups (three ration levels × two seasons), when the daily meal was presented in the post-dawn period the growth rate was lower than in trout fed at either mid-light or pre-dusk. No time-of-feeding effect was found when trout were fed excess rations. Specific growth rate (SGR) was not affected by feeding time, but was correlated with ration level; furthermore, there was a significant increase in SGR during the first section of the first trial and a significant decrease in the SGR throughout the duration of the second trial.Ration level was significantly correlated with condition factor, carcass visceral adipose tissue content and skeletal muscle lipid content, but there was no effect of the timing of the daily meal on these variables.     

Arctic charr in Britain and Ireland – 15 species or one?

Abstract –  From both a modern and a historical perspective there is little doubt that the Arctic charr, Salvelinus alpinus , in Britain and Ireland (as well as elsewhere) is a 'difficult' species. Historically 15 separate species have been recognised from populations in Britain and Ireland and there have been recent attempts to reassert these specific names. Here we review the evidence for the status of these 'species'. We conclude that the evidence for these 15 being afforded full species status is poor. However, both historical and contemporary data show that Salvelinus alpinus (Linnaeus 1758) in Britain and Ireland exhibits levels of variability in form that is much greater than in other species. We argue that a comprehensive genotypic and phenotypic survey of charr populations in Britain and Ireland is required to determine the full extent of variability and the status of populations with a view of providing suitable protection.     

Intraperitoneal injection of sulfur amino acids enhance the hepatic cysteine dioxygenase activity in rainbow trout (Oncorhynchus mykiss)

As part of the investigation into cysteine metabolism in fish, sulfur amino acids and their derivatives were injected intraperitoneally to fingerling rainbow trout (Oncorhynchus mykiss) to examine how the doses of these compounds affect the hepatic cysteine dioxygenase [EC 1.12.11.20] in this species. A dose of 0.25 mmol L-cysteine per 100 g body weight induced the enzyme activity as much as 2.5 times that of the control fish within 4h after the injection. The activity increased proportionally to the increasing dose of cysteine up to the dose of 0.15 mmol per 100 g body weight. The induction was observed to be rather specific to L-cysteine. These findings suggested that the cysteine sulfinate pathway might play an important role in the metabolism of excess cysteine in rainbow trout. The dosage of L-cysteine larger than 0.50 mmol per 100g body weight led to mortality of the fish. The pathway of cysteine catabolism was considered to function to prevent toxic accumulation of cysteine in rainbow trout, as in the case of mammals.     

Stress-induced changes in the affinity and abundance of cytosolic cortisol-binding sites in the liver of rainbow trout,Oncorhynchus mykiss (Walbaum), are not accompanied by changes in measurable nuclear binding

Plasma cortisol levels and the number (N_max) and affinity (K_d) of specific hepatic cortisol-binding sites were determined in rainbow trout subjected to chronic confinement stress for 14 days. Confinement significantly elevated plasma cortisol levels to 47.3 ± 13.5 ng ml^–1 within 24h and although levels declined to 8.0 ± 3.0 ng ml^–1 after 14 days, they were significantly higher throughout than levels in unstressed control fish (< 2.0 ng ml^–1). There was a 60% reduction in cytosolic N_max in stressed fish during the first 24h of confinement (35.8 ± 7.9 cf. 129.0 ± 15.2 fmol mg^–1 protein), a decline which was sustained at 7 days after the onset of stress but, although numbers of binding sites in the liver of stressed fish were still lower than in unstressed fish, the difference was no longer significant after 14 days of confinement. There was an accompanying significant rise in the K_d of cortisol binding in stressed fish during confinement, from 4.0 ± 0.6 nM at time 0 to 8.4 ± 0.8 nM after 24 h confinement. This increment in K_d was sustained at a level significantly higher than in control fish throughout the 14 day confinement period, despite marked reductions in cortisol levels and increases in N_max in stressed fish. Throughout the study, specific binding of cortisol could not be consistently detected in high-salt nuclear extracts from stressed or unstressed fish, suggesting either that high-affinity binding sites for cortisol were absent from these preparations, that receptors were present but unable to interact with ligand because they were occupied, or that receptors were present but not being extracted. These possibilities were investigated using a range of extraction procedures, by varying the temperature of incubation, by employing dexamethasone as ligand and by examining binding in purified, intact, nuclei. Estradiol was employed as a methodological control throughout and substantial amounts of specific estradiol binding were detected in all compartments and preparations. Specific cortisol-binding sites were detected in intact nuclei of both stressed and unstressed fish, at levels an order of magnitude lower than estradiol binding in the same preparations. These data demonstrate that activation of the pituitary-interrenal axis leads to significant changes in the nature of target-tissue binding of cortisol in rainbow trout, and reveal a clear difference in the subcellular distribution of binding-sites for estradiol and cortisol, which reflects the situation in mammalian tissues.     

Effect of ascorbic acid supplement in vitro onrainbow trout sperm viability

We evaluated motility and fertilizing ability of rainbow trout Oncorhynchus mykiss semen obtained from fish fed diets without ascorbic acid and a diet supplemented with 870 mg kg^{minus 1} of ascorbyl monophosphate. Semen was stored in vitro on ice (0 °C) during 14 days. The spermatozoa from the supplemented group had the highest motility and lowest decline in fertilizing ability after storage. Lack of a positive effect of exogenous vitamin C on semen in fish deficient in ascorbic acid (milt was supplemented with 50 mg l^–1 of ascorbic acid) suggests that the positive effect of ascorbic acid on semen quality is related to its long-term effects during spermatogenesis.     

Changes in the density and growth of brown trout (Salmo trutta) after intensive removal of sympatric Arctic charr (Salvelinus alpinus) in the sub‐Arctic lake Møkkelandsvatn,Norway

This study tests the basic hypothesis that the removal of charr, Salvelinus alpinus (L.), would cause an increase in both the growth and density of a sympatric trout population, Salmo trutta L. The charr population was characterised by slow‐growing individuals, with a high proportion of mature fish, that is typical for so‐called overpopulated populations. A total of 31,000 charr was removed from the lake in the period 1990–1992, and the density of younger trout (1+, 2+), but not older trout (3+, 4+), increased. The growth of older trout (3+, 4+) increased, but the evidence for similar growth increases of younger trout (1+, 2+) was limited. From 1989 to 1990, the proportion of trout increased from 30 to only 40% of the total catch, but from 1991 to 1994, it was significantly higher (60–80%) than that of charr. Total trout biomass increased to a maximum in 1992 and then decreased so that the biomass of 1994 was nearly similar to that of 1989, that is before the start of the charr removal. Back‐calculated lengths of trout from otoliths showed that 2+ and 3+ trout caught in the pelagic were growing consistently faster over previous years than those caught in the littoral, while this was not the case for the 4+ fish. Therefore, the hypothesis was partially supported; the growth rate of trout increased (age groups 1+ to 4+), while the density of juvenile trout (1+, 2+), but not the older trout (3+, 4+), increased after the removal of charr.     

Protein synthesis in trout liver is stimulated by both feeding and fasting

The response of protein synthesis in the liver of the rainbow trout to feeding and fasting was investigated in 3 experiments. In the first experiment, the fractional rate of protein synthesis (k _s ), %/day) appeared to cycle with daily feeding events being increased by 46%, 123%, and 72% at 1.5h, 3h, and 6h, after a meal. In Experiment 2, liver protein synthesis fell progressively with fasting to a basal level at 4d which was only 20% of the value at 3h after feeding. Liver weight (hepatosomatic index, HSI, % body weight), total RNA and total protein also fell gradually. Between 4d and 6d, both the RNA/protein ratio and the rate of protein synthesis were significantly increased (11% and 74%). At this time, however, there was also a large loss of liver protein suggesting a concomitant increase in protein breakdown. In the last experiment, when trout were pre-fed a low ration (0.6%/d for 2 wks, LR group), the HSI and liver total RNA and protein were largely unaffected by the 6d fast (i.e., relative to the body weight). In this group, however, protein synthesis at 3h was significantly higher than in fish pre-fed a high ration (1.5%/d, HR group). In addition, at 6d after feeding, protein synthesis had increased back to fed levels in the LR group only. It is concluded that protein synthesis in the liver of the trout is influenced both by feeding events and by ration size and also by the degree to which the trout is fasted.