Yolk-sac Fry Research Articles

Relationships between fish stock changes in the Baltic Sea and the M74 syndrome, a reproductive disorder of Atlantic salmon (Salmo salar)

Abstract Mikkonen, J., Keinänen, M., Casini, M., Pönni, J., and Vuorinen, P. J. 2011. Relationships between fish stock changes in the Baltic Sea and the M74 syndrome, a reproductive disorder of Atlantic salmon (Salmo salar). – ICES Journal of Marine Science, 68: 2134–2144. The M74 syndrome of Baltic salmon (Salmo salar), which appears as increased yolk-sac fry mortality (YSFM), impairs the reproduction of salmon stocks. Changes in the prey stocks of Baltic salmon in its two feeding areas, the southern Baltic Proper (BPr), where sprat (Sprattus sprattus) was the main prey species during the high incidence of M74, and the Bothnian Sea, where herring (Clupea harengus) is the dominant species, were analysed in relation to salmon growth and size and in relation to the incidence of M74. The high condition factor (CF > 1.05) of prespawning salmon predicted high YSFM. From the various stock factors of sprat and herring in the southern BPr, the biomass of sprat had the strongest positive relationships with the CF of prespawning salmon, and the total prey biomass with YSFM. It is concluded that the ample but unbalanced food resources for salmon in the BPr, primarily sprat, induce M74. By reducing the fishing pressure on cod (Gadus morhua) and by more effectively managing the sprat fishery in years when the cod stock is weak, the incidence of the M74 syndrome could be reduced and even prevented.

Tolerance of yolk sac and free swimming fry of African catfish ( Clarias gariepinus , Burchell 1822) to chemotherapeutic doses of formalin

This study reports tolerance levels and lethal concentrations of yolk sac and free swimming fry of African catfish (Clarias gariepinus) to different therapeutic doses of formalin. Comparative treatments were up to 2000 ppm for 15, 30 and 60 min exposure times and up to 150 ppm for 24 h exposure time for the second experiment on lethal concentrations. In both fry stages, higher survivals were recorded at short exposure times and at lower concentrations. The LC50 value for the yolk sac and free swimming fry was 130 and 90 ppm with total mortalities at concentrations beyond 150 and 125 ppm respectively. Although other concentrations and exposure times gave best performance in terms of survival, we recommend 15 min bath dip at 500 ppm for the yolk sac fry and 15 min at 600 ppm for the free swimming fry for routine use by rural fish farmers to reduce fry mortalities. Key words: Clarias gariepinus, formalin, free swimming fry, lethal concentration, yolk sac fry.

Spawning performance and seed production from hybridization between Oreochromis spilurus and the GIFT strain of the Nile tilapia Oreochromis niloticus

This study compared the spawning performance of four crosses between the salt-tolerant tilapia Oreochromis spilurus and the fast-growing genetically improved farmed tilapia (GIFT) strain of the Nile tilapia Oreochromis niloticus: (1) O. spilurus♀×O. spilurus♂ (SS); (2) Nile ♀× Nile ♂ (NN); (3) Nile ♀×O. spilurus♂ (NS) and (4) O. spilurus♀× Nile ♂ (SN). In each cross, males and females having mean weights of 157 and 115 g, respectively were stocked in 0.43 m3 tanks at a male to female ratio of 1:3. Seeds (unhatched eggs, yolk-sac fry and free swimming fry) were harvested biweekly for 127 days. Viable spawns resulted from all crosses. The NN cross produced the highest total seeds tank−1 (2890), seeds (kg female)−1 day−1 (48.3), seeds m−2 day−1 (23.3) and seeds female−1 day−1 (7.9), followed by the SS and SN crosses. The NS cross had the lowest fecundity. Lower spawning parameters in the NS and SN crosses may be attributed to the lower social compatibility between the males and females compared with that of the pure parents. The survival and growth of the offspring from the four crosses will be compared in seawater (37–40 g L−1) to assess whether hybrid vigor was produced.

Molecular Markers of Yolk Sac Fry Development in Nine Families of Lake Trout

Salmonids in certain areas of North America and northern Europe suffer from reproductive disturbances manifested through the death of yolk sac fry. These disturbances are referred to as early mortality syndrome (EMS) in the Great Lakes region and M74 in the Baltic Sea. Both of these syndromes have been associated with reduced concentrations of thiamine in affected females and their eggs. However, large variations in signs and mortality, both within and between the individual syndromes, have been reported. Yolk sac fry mortality (M74) in Atlantic salmon Salmo salar has been shown to be associated with reduced DNA binding of the hypoxia-inducible transcription factor 1 (HIF-1), reduced production of vascular endothelial growth factor (VEGF) protein, decreased capillary density, and down-regulation of adult-type globin gene transcription (which is responsible for the protein part of adult hemoglobin). One of the main effects of all of these changes is reduced oxygen transport to the tissues of affected fry. In this study, the developmental patterns of HIF-1 DNA binding, VEGF protein expression, and adult-type globin gene transcription were analyzed in nine family groups of Lake Michigan lake trout Salvelinus namaycush. The results indicate that HIF-1 DNA binding and globin gene transcription increase from hatch to the end of yolk sac stage. Interindividual and between-family biological variations were detected, especially in VEGF protein expression and globin gene transcription. Our results demonstrate the possibility of using these molecular markers in investigating the etiology of EMS and making comparisons between the mechanisms of different salmonid yolk sac fry mortalities.

Copper Sulfate Toxicity to Channel Catfish Fry: Yolk Sac versus Swim‐Up Fry

AbstractYolk sac and swim‐up fry from five separate spawns of channel catfish Ictalurus punctatus were exposed to dissolved copper sulfate (CuSO4) in a series of static toxicity bioassays to observe age sensitivity at 24 and 48 h in waters with two different chemistries at a temperature of 23.1 ± 0.47°C (mean ± SD). The two waters were (1) well water with a total alkalinity (as CaCO3) of 217 mg/L and a total hardness of 126 mg/L and (2) a 1:1 mixture of well water and deionized (WDI) water with a total alkalinity of 112 mg/L and a total hardness of 66 mg/L. Probit median lethal concentration (LC50) values were estimated with PoloPlus using the nominal CuSO4 concentrations. The mean 24‐h LC50 values for the yolk sac fry were 62.8 ± 37.1 mg of CuSO4/L in the well water and 10.2 ± 3.4 mg/L in the WDI water; the 24‐h LC50 values for the swim‐up fry were 13.5 ± 11.5 mg/L in well water and 4.3 ± 4.4 mg/L in WDI water. The mean 48‐h LC50 values for the yolk sac fry were 14.9 ± 5.0 mg/L in well water and 3.9 ± 1.6 mg/L in WDI water; the 48‐h LC50 values for the swim‐up fry were 3.5 ± 1.8 mg/L in well water and 1.5 ± 0.3 mg/L in WDI water. The yolk sac fry were about 4.6 times more tolerant of CuSO4 than the swim‐up fry at 24 h and 4.3 times more tolerant at 48 h. Fry were about 4.7 times (at 24 h) and 3.3 times (at 48 h) more sensitive to CuSO4 in water with low alkalinity and hardness (WDI water) than in water with high alkalinity and hardness (well water). The differences in LC50 values between the different spawns of each fry type and time within a water type are attributed to natural variation and channel catfish strain.

Oxidative Stress during Baltic Salmon Feeding Migration May Be Associated with Yolk-sac Fry Mortality

The wild populations of salmon in the Baltic Sea suffer from yolk-sac fry mortality (M74). M74 mainly occurs in populations spawning in rivers flowing to the Gulfs of Bothnia and Finland. On the basis of studies with fry, M74 may be caused by oxidative stresses. Because the eggs of M74-offspring-producing females have lower thiamine and astaxanthin levels and more oxidized fatty acids than eggs of females producing healthy offspring, oxidative stresses that adult salmon experience during their feeding migration may be decisive for the development of M74. In this study we have measured several oxidative stress parameters and have evaluated bothtemporal and regional differences in these parameters in salmon individuals during their feeding migration. At present, salmon feeding in the Gulf of Finland and in the Bothnian Sea are affected by oxidative stress as compared to populations feeding in the Baltic Proper. Moreover, the feeding population of salmon in the central Baltic Proper suffered much more from oxidative stress in 1999 than in 2006-2007. In 1999 the incidence of M74 was higher than that expected in 2007/2008. Oxidative stresses experienced by feeding salmon may thus be behind the development of M74.

Tissue-specific expression of aryl hydrocarbon receptor and putative developmental regulatory modules in Baltic salmon yolk-sac fry

The aryl hydrocarbon receptor (AhR) is an ancient protein that is conserved in vertebrates and invertebrates, indicating its important function throughout evolution. AhR has been studied largely because of its role in toxicology—gene expression via AhR is induced by many aromatic hydrocarbons in mammals. Recently, however, it has become clear that AhR is involved in various aspects of development such as cell proliferation and differentiation, and cell motility and migration. The mechanisms by which AhR regulates these various functions remain poorly understood. Across-species comparative studies of AhR in invertebrates, non-mammalian vertebrates and mammals may help to reveal the multiple functions of AhR. Here, we have studied AhR during larval development of Baltic salmon ( Salmon salar). Our results indicate that AhR protein is expressed in nervous system, liver and muscle tissues. We also present putative regulatory modules and module-matching genes, produced by chromatin immunoprecipitation (ChIP) cloning and in silico analysis, which may be associated with evolutionarily conserved functions of AhR during development. For example, the module NFKB-AHRR-CREB found from salmon ChIP sequences is present in human ULK3 (regulating formation of granule cell axons in mouse and axon outgrowth in Caernohabditis elegans) and SRGAP1 (GTPase-activating protein involved in the Slit/Robo pathway) promoters. We suggest that AhR may have an evolutionarily conserved role in neuronal development and nerve cell targeting, and in Wnt signaling pathway.

Humic substances modify accumulation but not biotransformation of pyrene in salmon yolk-sac fry

Humic substances may influence the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in aquatic environment. Relatively little is known how humic substances affect the biotransformation of PAHs in aquatic animals. Here we report how two different types of humic substances affected the accumulation of pyrene, a four-ringed PAH, to yolk-sac fry of landlocked salmon ( Salmo salar m. sebago). The accumulation of pyrene to yolk-sac fry tissues was inversely related to humic substance concentration in a short term (72 h) exposure. However, the biotransformation of pyrene was not affected by humic substances. Pyrene or humic subtances did not induce CYP1A activity in yolk-sac fry tissues contrasting to β-naphthoflavone, which was used as a positive control. Yolk-sac fry were capable to biotransform pyrene to phase I (1-hydroxypyrene) and phase II (pyrene-1-sulphate) products. Interestingly, glucuronide conjugate (i.e. pyrene-1-glucuronide) was not present in yolk-sac fry tissues. The concentration of parent pyrene and 1-hydroxypyrene remained the same throughout the experiment but the concentration of pyrene-1-sulphate more than doubled from 24 to 72 h. This finding suggests that salmon yolk-sac fry are not capable to excrete phase II biotransformation products or the excretion is very slow. Further, this could indicate that early life stage toxicity of many CYP1A inducing compounds is related to accumulation of phase II conjugates in fry tissues.

A revised description of Gyrodactylus cichlidarum Paperna, 1968 (Gyrodactylidae) from the Nile tilapia, Oreochromis niloticus niloticus (Cichlidae), and its synonymy with G. niloticus Cone, Arthur et Bondad-Reantaso, 1995

A recent infestation of Gyrodactylus cichlidarum Paperna, 1968 on yolk sac fry of Nile tilapia, Oreochromis niloticus niloticus (L.), in an isolated aquarium system in the U.K. resulted in high mortalities and provided an opportunity to study this species in greater detail. A tentative identification was made using the measurements and drawings of the ventral bar and hamuli provided in the original description; however, details on the morphology of the marginal hooks were lacking. A comparison of the gyrodactylid material collected from O. n. niloticus with the holotype of G. cichlidarum, the only known available specimen, from Mango tilapia, Sarotherodon galilaeus galilaeus (L.), confirmed its identity. Proteolytic digestion and image analysis of the opisthaptoral hard parts were used to obtain tissue-free, accurate measurements as part of a complete revised description of G. cichlidarumn. Further, a comparison of G. cichlidarum from both hosts with the holotype and several paratypes of Gyrodactylus niloticus Cone, Arthur et Bondad-Reantaso, 1995 cited as parasitizing captive stocks of Nile tilapia in the Philippines revealed the two species to be synonymous. An 803 bp fragment of the ribosomal internal transcribed spacers 1 and 2 and the 5.8S was obtained and is provided with the revised description. This is the first DNA sequence from a Gyrodactylus species originating from the African continent. The sequence is very divergent from other species in the genus and only the 5.8S sequence places it unambiguously in the genus Gyrodactylus. In addition to G. cichlidarum, two specimens of another morphological similar species of Gyrodactylus were also found on the UK held stock of O. n. niloticus. These latter specimens, Gyrodacrylus sp., differed from G. cichlidarum in having a longer hamulus point with a smaller hamulus aperture and possessing marginal hook sickles that had a shorter shaft with a longer point giving the sickles a more rounded, closed appearance.

M74 Syndrome in Baltic Salmon and the Possible Role of Oxidative Stresses in Its Development: Present Knowledge and Perspectives for Future Studies

Baltic salmon suffer from maternally transmitted yolk-sac fry mortality syndrome--M74. The incidence of M74 varies considerably on a year to year basis. In the 1990s the mortalities were 50-80% but in 2003-2005, below 10%. Before death, M74-affected fry have several typical symptoms. M74-eggs are characterized by low thiamine and carotenoid content, and affected fry show signs of oxidative stress. Although M74 is associated with thiamine deficiency and the symptoms of the fry can be alleviated with thiamine, the underlying causes of the syndrome have remained a mystery. We have studied the symptoms of M74 at the molecular level by investigating the global gene expression patterns using cDNA microarray and have quantified the changes in transcriptional regulation in M74-affected and healthy yolk-sac fry. Our and previous results suggest that M74 in Baltic salmon yolk-sac fry results from oxidative stresses disturbing several different developmental molecular pathways. Because the M74 syndrome is of maternal origin, factors in the Baltic Sea during salmon feeding and migration, i.e., the chemical composition of food, may be decisive in the development of M74. The possible mechanisms by which oxidative stresses may develop in adult salmon are discussed in the review.

Fatty acid composition of Oncorhynchus mykiss during embryogenesis and other developmental stages

Fatty acid compositions of rainbow trout Oncorhynchus mykiss (Walbaum, 1792) was determined during embryogenesis, yolk-sac fry, swim up fry and fry stages. Embryonic and yolk-sac development of fertilized eggs were followed until fry weighed 25 g and samples were taken from each stage to analyse fatty acid composition. Analyses of fatty acid composition were performed by gas chromatography mass spectrometry. Throughout all the developmental stages of O. mykiss important changes, such as an increase in the percentage of 18:2, 18:3 and 20:5 and as a decrease in the percentage of 14:0, 16:2, 20:0, 20:2, 20:3, 20:4 and 22:0 were observed in the amounts of fatty acid of developing eggs. During transition from the embryonic to the yolk-sac stage, an important increase in 20:0, 20:3, 20:5, 22:0 and a decrease in 18:3, 22:1 was determined between 45-day old embryo and yolk-sac fry. During transition from the 43 day yolk-sac stage to swim up stage, a decrease in the percentage of 18:0, 20:2 and an increase in the percentage of 14:0, 16:2, 18:2, 18:3 was seen. In all the observed stages, no qualitative but significant quantitative variations were determined in the fatty acid composition of O. mykiss. It may be concluded that 14:0, 16:0, 16:1, 18:0, 18:1 18, 20 and 22 polyunsaturated fatty acids are necessary for normal development of O. mykiss during their life stages.

Early rearing environment impacts cerebellar growth in juvenile salmon

The size and structure of an animal's brain is typically assumed to result from either natural or artificial selection pressures over generations. However, because a fish's brain grows continuously throughout life, it may be particularly responsive to the environmental conditions the fish experiences during development. Salmon are an ideal model system for studying these effects because natural habitats differ significantly from the hatchery environments in which these fish are frequently reared. For example, in the wild, salmon alevins (i.e. yolk-sac fry) are buried in the gravel, while hatchery environments lack this structural component. We show that the simple manipulation of adding stones to a standard rearing tank can dramatically alter the growth of specific brain structures in steelhead salmon alevins (Oncorhynchus mykiss). We found that alevins reared with stones grew brains with significantly larger cerebella than genetically similar fish reared in conventional tanks. This shift to a larger cerebellar size was, in turn, accompanied by changes in locomotory behaviors--behaviors that correlate strongly to the function of this brain region. We next show that hatchery fish reared in a more naturalistic setting in the wild had significantly larger brains than their lab-reared counterparts. However, relative cerebellar volumes were similar between wild-reared alevins and those reared in the complex treatment in the laboratory. Together our results indicate that, within the first three weeks of life, variation in rearing environment can result in brain differences that are commonly attributed to generations of selection. These results highlight the need to consider enrichment strategies when designing captive rearing facilities for both conservation and laboratory use.

CONTRIBUTION OF TROUT YOLK-SAC FRY (SALMO TRUTTA L.) ORIGINATING FROM WILD STOCK TO FISHING IN THE MOSELOTTE RIVER, FRANCE

The Moselotte River has been severely affected by human activity and in some of its stretches this has impaired reproduction of trout, which has added to an adverse effect on the trout population arising from a high fishing pressure by local anglers. To offset this problem, the local anglers annually release about 50,000 yolk-sac fry that have been derived from wild native breeding stock. It was possible to monitor the fry released in 1999 and 2000 using a method of mass marking by immersion in a fluoromarking agent (Alizarin Red S). The trout enter the fishery at 3 years and about 90% of the trout caught are three or four years old. Fish that had been released represented 25.5% and 36.7% of the catches respectively in 2002 and 2003, two percentages that do not differ significantly. This proportion varied according to the location in the river. The age structure of the marked fish that were caught was similar to that of fish hatched in the wild.

Pharmacokinetics of thiamine in female Baltic salmon ( Salmo salar L.) broodfish

A thiamine deficiency disease termed M74 syndrome affects the yolk-sac fry of wild and feral Baltic salmon. However, very little is known about the pharmacokinetics of thiamine in salmon. This study examined the pharmacokinetics of thiamine hydrochloride injected intraperitoneally into feral and farmed Baltic salmon females preparing for spawning. The total thiamine concentrations in the eggs and white muscle of feral females were only half of those in the farmed fish after injection. The relative inefficiency of the incorporation of thiamine into the eggs in feral Baltic salmon may be a predisposition factor for M74 syndrome. The relative bioavailability of intraperitoneally-injected thiamine hydrochloride was shown to be ca. 94% of that administered intra-aortically. A far lower intraperitoneal dose (ca. 20 mg kg −1 fish) than currently used was shown to elevate the total thiamine concentration in the eggs above the critical threshold of M74 syndrome.

Observations on the reproductive performance of three mouth-brooding tilapia species in low-salinity underground water

The reproductive performance and seed production of three mouth-brooding tilapia species, Oreochromis spilurus (Günther), Oreochromis aureus (Steindachner) and Taiwanese red tilapia hybrid, were compared in low-salinity underground water (3–5 g L−1) to select species with the highest reproductive rate. Two-year-old males and females having average body weights of 454 and 259 g, respectively, were stocked in 2-m3 fibreglass breeding tanks (two tanks per species) at 1:3 male to female sex ratio and at average density of three fish m−2. Seeds (unhatched eggs; yolk-sac fry and the swim-up fry) were collected weekly for 112 days. The results showed O. spilurus to have significantly higher (P<0.05) mean spawning parameters expressed as total seed tank−1 (84 154), seed kg female−1 day−1 (284), seed m−2 day−1 (190.3) and seed female−1 day−1 (76.3), than O. aureus and red tilapia. Monthly seed production in O. spilurus and red tilapia gradually increased from May, peaked in July and declined in August, while in O. aureus, it continued to decrease from May to August. In this study, the observed production levels of seed in O. spilurus were among the highest levels reported for tilapia; therefore, O. spilurus could be selected as a potential candidate for mass seed production in commercial tilapia hatcheries.

Baltic salmon ( Salmo salar) yolk-sac fry mortality is associated with disturbances in the function of hypoxia-inducible transcription factor (HIF-1α) and consecutive gene expression

Baltic salmon ( Salmo salar) suffer from abnormally high yolk-sac fry mortality designated as M74-syndrome. In 1990s, 25–80% of salmon females, which ascended rivers to spawn, produced yolk-sac fry suffering from the syndrome. Symptoms of M74-affected fry include neurological disturbances, impaired vascular development and abnormal haemorrhages. The latter symptoms are observed in mammalian embryos if the function of hypoxia inducible transcription factor (HIF-1α), its dimerization partner aryl hydrocarbon nuclear translocator (ARNT) or target gene vascular endothelial growth factor (VEGF) is disturbed. To study the possible involvement of HIF-1α and its target gene VEGF in the development of the syndrome, we collected healthy and M74-affected wild Baltic salmon yolk-sac fry and analyzed HIF-1α mRNA and protein expression, HIF-1α DNA-binding, target gene VEGF protein expression, and blood vessel density in both groups at different stages of yolk-sac fry development. In addition, since Baltic salmon females contain organochlorine contaminants, which have been suggested to be the cause of M74 syndrome via the aryl hydrocarbon receptor (AhR)-dependent gene expression pathway, we studied AhR protein expression, AhR DNA-binding and target gene CYP1A protein expression. Since the parents of both healthy and M74-affected wild fry will have experienced the organochlorine load from the Baltic Sea, hatchery-reared fry were included in the studies as an additional control. The results show that the vascular defects observed in fry suffering from M74 are associated with reduced DNA-binding activity of HIF-1α and subsequent downregulation of its target gene vascular endothelial growth factor (VEGF). In addition, also AhR function is decreased in diseased fry making it unlikely that symptoms of M74-affected fry would be caused by an upregulation of xenobiotically induced AhR-dependent gene expression pathway.

Baltic salmon (Salmo salar) yolk-sac fry mortality is associated with disturbances in the function of hypoxia-inducible transcription factor (HIF-1$alpha;) and consecutive gene expression

Baltic salmon (Salmo salar) suffer from abnormally high yolk-sac fry mortality designated as M74-syndrome. In 1990s, 25–80% of salmon females, which ascended rivers to spawn, produced yolk-sac fry suffering from the syndrome. Symptoms of M74-affected fry include neurological disturbances, impaired vascular development and abnormal haemorrhages. The latter symptoms are observed in mammalian embryos if the function of hypoxia inducible transcription factor (HIF-1α), its dimerization partner aryl hydrocarbon nuclear translocator (ARNT) or target gene vascular endothelial growth factor (VEGF) is disturbed. To study the possible involvement of HIF-1α and its target gene VEGF in the development of the syndrome, we collected healthy and M74-affected wild Baltic salmon yolk-sac fry and analyzed HIF-1α mRNA and protein expression, HIF-1α DNA-binding, target gene VEGF protein expression, and blood vessel density in both groups at different stages of yolk-sac fry development. In addition, since Baltic salmon females contain organochlorine contaminants, which have been suggested to be the cause of M74 syndrome via the aryl hydrocarbon receptor (AhR)-dependent gene expression pathway, we studied AhR protein expression, AhR DNA-binding and target gene CYP1A protein expression. Since the parents of both healthy and M74-affected wild fry will have experienced the organochlorine load from the Baltic Sea, hatchery-reared fry were included in the studies as an additional control. The results show that the vascular defects observed in fry suffering from M74 are associated with reduced DNA-binding activity of HIF-1α and subsequent downregulation of its target gene vascular endothelial growth factor (VEGF). In addition, also AhR function is decreased in diseased fry making it unlikely that symptoms of M74-affected fry would be caused by an upregulation of xenobiotically induced AhR-dependent gene expression pathway.

The susceptibility of early developmental phases of an acid-tolerant and acid-sensitive fish species to acidity and aluminum

The mortality of roach ( Rutilus rutilus) embryos increased during the early embryonic phase following exposure to Al and acidity from pH 6.7 to 5.0. No roach hatched at pH<5.00 or at pH 5.00 in the presence of Al. By contrast, increased embryonic mortality in pike ( Esox lucius) occurred mainly during and after the normal hatching period due to the acidity-dependent prolongation and inhibition of hatching at pH 4.00. Newly hatched fry of both species were more sensitive to Al than the embryos. A reduction in the development of yolk-sac fry occurred in pike at pH 4.00 and in roach at pH 5.00, and in the presence of Al at pH⩽5.00 and pH⩽5.75, respectively. Thus, the most susceptible early developmental phase to acidity differed between the acid-sensitive roach and the acid-tolerant pike, although the newly hatched fry was the developmental phase most sensitive to Al for both species.

Bisphenol A induces yolk-sac oedema and other adverse effects in landlocked salmon ( Salmo salar m. sebago) yolk-sac fry

Accumulation and toxicity of waterborne bisphenol A were studied in landlocked salmon ( Salmo salar m. sebago) yolk-sac fry. In a short-term (96 h) exposure to five bisphenol A concentrations yolk-sac fry had higher accumulation rates and bioconcentration factors (BCF 96) than earlier studies have shown for salmon eggs. Furthermore, the conditional uptake rate constant tended to decrease as exposure concentration increased. Fry were also exposed to bisphenol A for 42 days at three concentrations (10, 100 and 1000 μg/l), and changes in behaviour, morphology and histological structure were observed. After 6 days of exposure, the highest concentration (1000 μg/l) of bisphenol A caused fluid accumulation (oedema) in the yolk sac and haemorrhages in the front part of the yolk sac and in the head around the gill arches. Later on, the fry at 1000 μg/l showed phlegmatic behaviour and had darker skin coloration than the fry in the other treatments. At the two highest concentrations (100 and 1000 μg/l) histological changes were seen in liver cell nuclei, where strongly stained fragments were observed. In the control fry and the fry exposed to 10 μg/l the nucleolus was clearly visible and spherical in shape and no strongly stained fragments were present. This study shows that high concentrations of bisphenol A may have both morphological and histological effects on salmon yolk-sac fry.

Effects of environmental salinity and 17α-methyltestosterone on growth and oxygen consumption in the tilapia, Oreochromis mossambicus

Effects of environmental salinity and 17α-methyltestosterone (MT) on growth and oxygen consumption were examined in the tilapia, Oreochromis mossambicus. Yolk-sac fry were collected from brood stock in fresh water (FW). After yolk-sac absorption, they were assigned randomly to one of four groups: FW, MT treatment in FW, seawater (SW) and MT treatment in SW. All treatment groups were fed to satiation three times daily. The fish reared in SW (both control and MT-treated groups) grew significantly larger than either group in FW from day 43 throughout the experiment (195 days). The fish fed with MT added to their feed grew significantly larger than their respective controls from day 85 in FW and in SW until the end of the experiment. The routine metabolic rate (RMR) was determined monthly from month 2 (day 62) to month 5 (day 155). A significant negative correlation was seen between RMR and body mass in all treatment groups. Among fish of the same age, the SW-reared tilapia had significantly lower RMRs than the FW-reared fish. The MT-treated fish in SW showed significantly lower RMRs than the SW control group at months 3–5, whereas MT treatment in FW significantly increased the RMR at month 3. Comparison of regression lines between RMR and body mass indicates that MT treatment in FW caused a significant increase in oxygen consumption at a given mass of the fish, whereas MT treatment was without effect on RMR in SW-reared fish. These results clearly indicate that SW-rearing and MT treatment accelerate growth of tilapia, and that RMR decreases as fish size increased. It is also likely that the increased RMR and growth in MT-treated tilapia in FW may be due to the metabolic actions of MT, although the reason for the absence of MT treatment in SW is unclear.