Aggressiveness and kinship in brown trout (Salmo trutta) parr

In a series of experiments, kin-biased behavior of young browntrout (Salmo trutta) was observed. The aggressiveness shownby groups of familiar siblings (siblings reared together sincefertilization) and groups of unfamiliar siblings (siblings rearedapart since fertilization) was significantly lower comparedto that of mixed groups of two unrelated sibling groups (offspringof two different pairs of parents). The evolution of kin-biasedbehavior, as shown by a reduction in aggressiveness, is assumedto have evolved through a kin-selective mechanism.[Behav Ecol7: 445-450 (1996)]     

A 27-year study of brown trout population dynamics and exploitation in Lake Songsjøen, central Norway

From 1968–1984 (period I), a brown trout Salmo trutta , population in a 70-ha oligotrophic lake in central Norway was exploited using larger mesh gill-nets selectively removing the larger fish. From 1985–1994 (period II), intermediate sized fish were removed using smaller-mesh sizes gill-nets. Fishing mortality and CPUE were correlated positively with effort and numbers of fish >3 years old for period II. The gill-net catchability was correlated negatively with spawner biomass and number of trout >3 years old. The significant positive correlation between natural mortality and stock biomass and spawning stock biomass indicated density-dependent mortality. The significant correlation between spawning stock and recruitment described by the Ricker model, indicated density-dependent recruitment of 1-year-old trout. The fishing regimes in the two periods affected the population dynamics and density differently. Selective removal of smaller fish permitted the larger fish to survive, and was beneficial in reducing fish density and maintaining stocks at low levels, consequently, achieving the expected increase in fish growth rates.     

Histopathological alterations and parasite infection in fish: indicators of multiple stress factors

Within the scope of the multidisciplinaryresearch project Valimar (1995–1999), thepresent study emphasizes the use ofhistopathological investigations to evaluatethe effects of the different chemical impactof two small streams on the general health andcondition of the two sentinel fish species,brown trout (Salmo trutta f.fario) and loach (Barbatula barbatula).Parasitological investigations were alsoincluded to assess a possible relationshipbetween toxicant exposure, parasitic load, andthe occurence of histopathological organchanges. According to the multitiered approachof the Valimar project, fish from the field,individuals exposed to stream water undersemi-field conditions, and fish fromlaboratory experiments were investigated.Under semi-field conditions, thehistopathological responses in brown troutproved to reflect the different levels ofcontamination of the two small streams moreclearly than those detected in loach. Whencaptured from the field, both fish speciesrevealed, in most cases, a higher degree ofhistopathological alterations than thoseindividuals exposed at the respective siteunder semi-field conditions. Simulation of thetoxic load of the more polluted stream in alaboratory experiment did not result in thesame kind of tissue lesions in brown trout asin the field and semi-field investigations.Whereas results from the laboratoryexperiments could be specified astoxicant-induced, the histopathologicalalterations in fish from both semi-field andfield studies represent stress responses whichintegrate the effects of various abiotic andbiotic stress factors including both toxicantsand parasitic diseases.     

Diurnal rhythms of plasma growth hormone,somatostatin, thyroid hormones,cortisol and glucose concentrations in rainbow trout,Oncorhynchus mykiss,during progressive food deprivation

Abstract

The diurnal patterns of changes in plasma cortisol, growth hormone (GH), somatostatin‐14 (SRIF), thyroid hormones (L‐thyroxine, T₄ and triiodo‐L‐thyronine, T₃) and glucose were investigated in rainbow trout, Oncorhynchus mykiss, both during single meal‐feeding and during a progressive fast of 13 weeks. All measured variables exhibited a diurnal pattern in fed rainbow trout, most of which appeared to be correlated with the time of feeding (30–60 min after the onset of light), while additional changes, associated with the scotophase were also found for cortisol. Although fasting had no affect on mean daily plasma cortisol or SRIF concentrations, there was a progressive increase in mean daily plasma GH concentrations and a progressive decrease in mean daily plasma thyroid hormone and glucose concentrations associated with fasting. However, for GH, significant changes were not evident until week 10 of the fast. In addition, fasting appeared to phase‐shift the diurnal patterns of plasma GH, cortisol and glucose concentrations; the consequence of such a shift is that conclusions as to the effects of fasting, if based on a single time of sampling, may be flawed.     

Dietary Modifications of Phospholipid Composition and Biophysical Properties of the Brush Border Membrane Along the Trout Intestine

Brush border membranes (BBM) are isolated from middle and posterior intestine of trout fed either an essential fatty acid-rich diet or a saturated one. The different phospholipid classes are separated, and their fatty acid composition is determined. Fluorescence anisotropy studies are performed using two lipid fluorophores, namely diphenylhexatriene (DPH) and trimethyl-aminodiphenylhexatriene (TMA-DPH). The results indicate that the usual parameters affecting the lipid fluidity such as the phospholipid:protein (PL:PROT), cholesterol:phospholipid (CHOL:PL), and sphingomyelin:phosphatidylcholine (SP:PC) ratios and the unsaturation of the acyl chains are sufficient to explain the fluidity values determined using DPH, but not those obtained with TMA-DPH as a probe. This fluorophore is assessed to be localized only in the external leaflet of the membrane. Hence, it will be affected by the composition of the major phospholipids of this leaflet, sphingomyelin and phosphatidylcholine.     

Anadromous trout threatened by whitefish gill‐net fisheries in the northern Baltic Sea

We estimated the effect of the gill‐net fisheries targeted at whitefish (Coregonus sp.) on anadromous sea trout, Salmo trutta, in the Gulf of Bothnia, Baltic Sea using separate data for fish species. The analysis of sea trout captures was based on tagging and recapture data collected in 1998–2011, while whitefish data were derived from individual samples of commercial fisheries from the same period. The mesh sizes used in gill‐net fishing and the seasonal and temporal distributions of recaptured sea trout and sampled whitefish were compared in the northern and southern Gulf of Bothnia. The trout had typically spent 1–2 years at sea, and they were mainly immature with a median body length of 40–43 cm at the time of recapture in gill nets. Despite the increase in the minimum permitted landing size from 40 to 50 cm in 2008, the median length of recaptured trout remained unchanged during the study period. Most (59%) of the gillnetted trout were caught in the southern Gulf of Bothnia in gill nets with mesh sizes of 40–45 mm, which were also used in the whitefish fishery (72%). In the northern Gulf of Bothnia, nets with a smaller mesh size of 25–39 mm took 83% of the whitefish catch and 39% from recaptured trout. In both areas, the overlap in mesh sizes used to gill‐net catch whitefish and sea trout increased during the study period. There were clear seasonal and areal differences in the relative probability of sea trout being captured in gill nets, suggesting that carefully tailored spatial and temporal restrictions on gill‐net fisheries could provide a tool to protect young sea trout without causing intolerable difficulties for the fisheries targeting other species.     

Growth hormone stimulates hepatic lipid mobilization in rainbow trout,Oncorhynchus mykiss

Rainbow trout were used to characterize the direct influence of growth hormone on hepatic lipid mobilization in vitro. Liver was removed from fish fasted 72 h, sliced into 1-mm³ pieces and incubated in Hanks' medium containing ovine or salmon growth hormone (0.28 ng·ml^-1–28 g·ml^-1). Lipid mobilization, resulting from triacylglycerol hydrolysis, was evaluated by fatty acid and glycerol release into culture medium. Control rates of fatty acid release and glycerol release were 0.95±0.16 (mean ± SE) and 0.88±0.28 mol·l^-1·mg fresh weight, respectively. Both ovine growth hormone (28 ng·ml^-1) and salmon growth hormone (28 ng·ml^-1) stimulated fatty acid release into culture medium, increasing rates by 112% and 97%, respectively, during the course of a 24-h incubation. Glycerol release was similarly augmented by growth hormone treatment. Growth hormone-stimulated metabolite release became evident within 12 h and persisted for up to 72 h. The presence of amino acids in the culture medium potentiated the lipolytic action of growth hormone. Ovine growth hormone (28 ng·ml^-1) in the presence of amino acids stimulated a 53% increase in fatty acid, and a 108% increase in glycerol, release over rates observed in the absence of amino acids. Salmon growth hormone (28 ng·ml^-1) in the presence of amino acids stimulated a 53% increase in fatty acid, and a 44% increase in glycerol, release over rates observed in the absence of amino acids. Ovine growth hormone (28 ng·ml^-1) also stimulated gluconeogenesis, as indicated by a 75% increase in phosphoenolpyruvate carboxykinase activity in liver pieces incubated in the presence of amino acids. These results indicate that growth hormone directly stimulates lipid breakdown in the liver of trout and that amino acids potentiate growth hormone-stimulated lipolysis.Abbreviations AA amino acid(s) - dGDP deoxy-guanosine diphosphate - ED ₅₀ 50% effective dose - FA fatty acid(s) - fw fesh weight - GH growth hormone - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid - MS-222 tricaine methanesulfonate - MEM minimum essential medium - oGH ovine growth hormone - PEPCK phosphoenolpyruvate carboxykinase - PK_c protein kinase C - rpm revolutions per minute - sGH salmon growth hormone - TG triacylglycerol - w/v weight per volume This paper was presented in abstract form at the Annual Meeting of the American Society of Zoologists, Dec. 26–30, 1991, Atlanta, GA     

Plasma levels of gonadotropin and 17α,20β-dihydroxy-4-pregnen-3-one in relation to spawning behaviour of rainbow trout, Oncorhynchus mykiss(Walbaum)

Manipulation of the opportunity to spawn was used to investigate the relationship between endocrine events, egg viability and spawning behaviour in female rainbow trout. Females were prevented from spawning by isolating them from males and gravel for up to 21 days after ovula- tion. Blood samples were taken before pairing with a male, at the onset of nesting activity, and at the completion of spawning. Plasma hormone levels of gonadotropin (GtH) and 17α,20β-dihydroxy-4-pregnen-3-one (17,2OP) were measured by specific radioimmunoassays. There were no qualitative or quantitative differences in the spawning behaviour of females paired on the day of ovulation or 7. 14, or 21 days after ovulation. There was a general decrease in the viability of eggs with increasing retention times. In females paired on the day of ovulation, or after 7 or 14 days, GtH levels increased with the onset of nesting behaviour and declined as fish reached the post-spawning condition. By day 21, GtH levels before pairing were significantly higher than prepairing levels in the other three treatment groups, and did not increase at the onset of nesting, or decrease in post-spawning fish. Plasma 17,20P remained high in prepairing and nesting samples of all four groups and declined to low levels in fish in post-spawning condition. In females paired on the day of ovulation there was a significant increase in 17,20P from the prepairing to the nesting stage. These results suggest that 17,20P plays a key role in the synchronization of behavioural and maturational events at the time of spawning.     

Critical thermal minima and maxima of three freshwater game-fish species acclimated to constant temperatures

A total of 120 critical thermal maxima (CT maxima) and 120 critical thermal minima (CT minima) were determined for channel catfish, largemouth bass and rainbow trout acclimated to three constant temperatures: 20, 25 and 30 °C in catfish and bass, and 10, 15 and 20 °C in trout. Highest mean CT maximum and lowest mean CT minimum measured over these acclimation temperatures were 40.3 and 2.7 °C (catfish), 38.5 and 3.2 °C (bass) and 29.8 and ∼ 0.0 °C (trout). Temperature tolerance data were precise with standard deviations generally less than 0.5 °C. Channel catfish had the largest thermal tolerance scope of the three species while rainbow trout had the lowest tolerance of high temperatures and the highest tolerance of low temperatures. In all species CT minima and CT maxima were highly significantly linearly related to acclimation temperature. Within each species, slopes relating CT maxima to acclimation temperature were approximately half as large as those relating CT minima to acclimation temperature, suggesting that acclimation temperature has a greater influence on tolerance to low rather than high temperatures. Slopes relating both CT minima and CT maxima to acclimation temperature for the two warm-water species were similar and approximately twice those for the rainbow trout. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of exogenous estradiol-17β on early growth and gonadal development of diploid and triploid female rainbow trout (Oncorhyncus mykiss)

Triploidy is a viable condition in teleosts. However, in many salmonids, the triploid condition in the female results in sterility as gametogenesis appears to be disrupted. Although the underlying mechanisms regulating the gonadal development of teleosts have not been clearly elucidated, the reversal of phenotypic sex by the administration of the appropriate exogenous steroid during early development supports the argument that gonadal steroids play a pivotal role in sexual differentiation and subsequent gonad development in these fish. To determine whether the failure of normal ovarian development in triploid female rainbow trout (Oncorhynchus mykiss) is due to an absence or reduction of endogenous sex steroids, ovarian morphology was compared between diploid and triploid juvenile rainbow trout treated with exogenous estradiol-17β (E₂). The ovaries of both untreated and E₂ treated diploid fish, at 145 days post-fertilization, contained synchronously developing oocytes in the perinucleolar stage, whereas ovaries from untreated and estradiol-treated triploid fish of the same age were considerably smaller and devoid of developing oocytes. No differences in the ovaries of triploid untreated fish and triploid fish treated with E₂ were observed. It is reported that exposure to exogenous E₂ during the period of gonadal differentiation is not sufficient to induce oocyte development in triploid rainbow trout. © 1996 Wiley-Liss, Inc.