Free plasma thyroxine levels in coho salmon, Oncorhynchus kisutch, during parr-smolt transformation: comparison with total thyroxine, total triiodothyronine, and growth hormone levels

Free plasma thyroxine (FT₄) levels were measured in coho salmon, Oncorhynchus kisutch, during parr-smolt transformation (smoltification) using an equilibrium dialysis system followed by a radioimmunoassay. The FT₄ data were correlated to total plasma thyroxine (TT₄), triiodothyronine (TT₃), and growth hormone (GH). Plasma samples were taken weekly from early April to late May, when the salmon where released from the hatchery. Free thyroxine and GH levels increased gradually through smoltification. TT₄ levels increased significantly in mid-April and in mid-May. TT₃ levels increased in April and remained elevated until late-May after which they declined to the lowest levels. During the first increase in TT₄ levels, FT₄ levels remained low and TT₃ levels did not increase until FT₄ levels increased in late-April. In addition, after TT₄ levels decreased in late May, FT₄ levels remained elevated. These data show that there are differences between the plasma FT₄ and TT₄ profiles during smoltification. Nevertheless, regression analysis indicates that FT₄ levels are highly correlated to the increases in the levels of GH (r=0.73) and TT₄ (r=0.70). In addition, GH is less correlated to TT₄ and TT₃ (r=0.24 and r=–0.46, respectively) compared with FT₄ (r=0.73), suggesting a close relationship between the increases of FT₄ and GH. In addition, these data suggest that this method of measuring free plasma thyroxine may provide a new tool for studying the timing of thyroid hormone action and regulation during parr-smolt transformation in salmonids.     

Polyunsaturated fatty acid metabolism in Atlantic salmon (Salmo salar) undergoing parr-smolt transformation and the effects of dietary linseed and rapeseed oils

Duplicate groups of Atlantic salmon parr were fed diets containing either fish oil (FO), rapeseed oil (RO), linseed oil (LO) or linseed oil supplemented with arachidonic acid (20:4n-6; AA) (LOA) from October (week 0) to seawater transfer in March (week 19). From March to July (weeks 20–34) all fish were fed a fish oil-containing diet. Fatty acyl desaturation and elongation activity in isolated hepatocytes incubated with [1-¹⁴C]18:3n-3 increased in all dietary groups, peaking in early March about one month prior to seawater transfer. Desaturation activities at their peak were significantly greater in fish fed the vegetable oils, particularly RO, compared to fish fed FO. Docosahexaenoic acid (22:6n-3:DHA) and AA in liver and gill polar lipids (PL) increased in all dietary groups during the freshwater phase whereas eicosapentaenoic acid (20:5n-3; EPA) increased greatly in all groups after seawater transfer. The AA/EPA ratio in tissue PL increased up to seawater transfer and then decreased after transfer. AA levels and the AA/EPA ratio in gill PL were generally higher in the LOA group. The levels of 18:3n-3 in muscle total lipid were increased significantly in the LO, LOA and, to a lesser extent, RO groups prior to transfer but were reduced to initial levels by the termination of the experiment (week 34). In contrast, 18:2n-6 in muscle total lipid was significantly increased after 18 weeks in fish fed the diets supplemented with RO and LO, and was significantly greater in the FO and RO groups at the termination of the experiment. Gill PGF production showed a large peak about two months after transfer to seawater. The production of total PGF post-transfer was significantly lower in fish previously fed the LOA diet. However, plasma chloride concentrations in fish subjected to a seawater challenge at 18 weeks were all lower in fish fed the diets with vegetable oils. This effect was significant in the case of fish receiving the diet with LOA, compared to those fed the diet containing FO. The present study showed that during parr-smolt transformation in Atlantic salmon there is a pre-adaptive increase in hepatocyte fatty acyl desaturation/elongation activities that is controlled primarily by environmental factors such as photoperiod and temperature but that can also be significantly modulated by diet. Feeding salmon parr diets supplemented with rapeseed or linseed oils prevented inhibition of the desaturase activities that is induced by feeding parr diets with fish oils and thus influenced the smoltification process by altering tissue PL fatty acid compositions and eicosanoid production. These effects, in turn, had a beneficial effect on the ability of the fish to osmoregulate and thus adapt to salinity changes.     

Propylthiouracil-induced hypothyroidism in coho salmon, Oncorhynchus kisutch: effects on plasma total thyroxine, total triiodothyronine, free thyroxine, and growth hormone

Thyroid hormones transiently increase during parr-smolt transformation in coho salmon, Oncorhynchus kisutch, and are believed to trigger morphological, physiological, behavioural, and neural changes. The effectiveness of propylthiouracil (PTU) to induce hypothyroidism in smolting coho salmon was determined by immersing coho salmon, Oncorhynchus kisutch, in 30 mg l–1 PTU from May 1, two weeks prior to the consistent annual total thyroxine (TT4) peak in mid-May, until the last sampling date. Plasma was obtained at two sampling dates from control and PTU -treated coho salmon: May 15, during the plasma TT4 peak; and May 26, after the TT4 peak. Radioimmunoassays were used to measure plasma TT4, total triiodothyronine (TT3), free thyroxine (FT4), and salmon growth hormone (sGH). The PTU -treatment inhibited the natural smoltification-related increases in plasma TT4, TT3 and GH levels compared with controls, but PTU-treatment did not affect these hormone levels when they were low. PTU -treatment increased FT4 and decreased TT3 and sGH levels in the May 26 sample. In the May 15 sample, FT4 levels were unaffected by PTU-treatment, whereas TT4 levels were decreased. These data demonstrate the ability of PTU to induce hypothyroidism in salmonids as shown by the decrease in TT4 and TT3. These data demonstrate that PTU treatment by immersion can induce hypothyroidism in salmonids as shown by: (1) the inhibition of the natural increases of TT4 and TT3; (2) the increase in FT4 levels corresponding to the lowered TT3 levels, suggesting an inhibition of thyroxine 5-monodeiodinase activity. We also show for the first time that PTU treatment can lower plasma GH levels in salmonids. This lowering of plasma GH level is associated with the decrease in TT3 levels and the increase in FT4 levels. The PTU induced lowering in GH levels may contribute to the observed changes in FT4 and TT3, since GH is known to increase thyroxine 5-monodeiodinase activity.     

Serum thyroxine,estradiol-17β, and testosterone profiles during the parr-smolt transformation of masu salmon,Oncorhynchus masou

Changes in serum thyroxine (T₄), estradiol-17β (E₂) and testosterone (T) levels during the parr-smolt transformation (smoltification) were investigated in the masu salmon (Oncorhynchus masou) in 1985 and 1987. T₄ showed a peak in levels at the early stage of smoltification and E₂ and T levels peaked almost at the same time. There were no significant differences between the concentrations of serum hormones in female and males. During smoltification, germ cells in the peri-nucleolus and spermatogonia stage were present in the ovary and testis, respectively. These results suggest that E₂ and T may be involved in smoltification in the masu salmon.     

Changes in intestinal fluid transport in Atlantic salmon (Salmo salar L) during parr-smolt transformation

We examined changes in fluid transport by the intestine of Atlantic salmon (Salmo salar L) undergoing parrsmolt transformation during springtime. In vitro measurements of fluid transport rate (J_v) across non-everted middle and posterior intestinal sac preparations were made in late April and early June 1990 and from February through June 1991 for juvenile smolting fish. Intestinal J_v was also compared between parr- and smolt-stage salmon in both years. To evaluate the osmoregulatory role of the intestine, J_v was measured for smolts adapted to seawater and their cohorts remaining in fresh water. The middle intestine of smolting fish underwent a significant decrease in fluid transport during the springtime, while posterior intestinal J_v significantly increased. Parr-stage fish decreased J_v in the middle intestine during springtime similar to smolts. However, the posterior intestinal J_v of smolts showed a significant increase over the parr around the peak smolt period in both years. Seawater-adapted smolts generally exhibited posterior intestinal J_v approximately double that of freshwater cohorts. A decrease over time shown for the middle intestine, together with the increased J_v in the posterior intestine preceding and after seawater entry, suggests the development of a functional regionalization during parr-smolt transformation, with the posterior intestine taking on increased importance in osmoregulation in seawater.     

Effects of triiodothyronine and propylthiouracil on thyroid function and smoltification of coho salmon (Oncorhynchus kisutch)

Yearling coho salmon (Oncorhynchus kisutch) were fed diets containing triiodothyronine (T₃; 4 or 12gmg), propylthiouracil (PTU; 1.5 or 6.0 mg/g), or both T₃ (12g/g) and PTU (1.5 mg/g) from January 10 to May 29. Plasma T₄ and T₃, concentrations were maintained within normal physiological limits in all groups of treated fish. Increases in plasma thyroxine (T₄) occurred in late April in groups receiving the high dose of T₃ or PTU, or the combination of T₃, and PTU. Peaks of plasma T₄ occurred in May in the other groups. Thyroid follicle epithelial cell height was increased in the groups in the following order: highest; PTU (6.0 mg/g), PTU (1.5 mg/g), PTU + T₃, control, T₃ (4gmg/g), T₃ (12g/g); lowest. In March specific binding of T₃ by liver nuclei was not affected by treatment with T₃ (12g/g) but was decreased 30% by treatment with PTU (6.0g/g). Body growth, food conversion efficiency, and pigmentary changes were increased by T₃ (12g/g), decreased dose-dependently by PTU, and unaffected by the other dietary treatments. All treatments altered body proximate composition. Food consumption and the ability to osmoregulate in seawater were decreased in fish fed 6.0 mg/g PTU, but were unaffected by the other dietary treatments. These results suggest that during smoltification: 1) Thyroid hormones may be involved in control of thyroidal function and body growth and pigmentary changes, 2) Hypo-osmoregulatory competence is not further stimulated by exogenous T₃ and 3) PTU does not block T₄ synthesis but may block T₃, action by interfering with nuclear T₃ binding.     

Atlantic salmon (Salmo salar) prolactin cDNA sequence and its mRNA expression after transfer of fish between salinities

The Atlantic salmon (Salmo salar) has a life cycle that involves inhabiting both fresh and salt water. The control and maintenance of ionic balance is under control of the endocrine system. Prolactin is reportedly an important hormone for the ionic balance of salts in the body fluids of fish, especially during the periods of time spent in fresh water. An Atlantic salmon pituitary cDNA library was constructed in gt 11, from which a full length Atlantic salmon prolactin cDNA was isolated using a chinook salmon (Oncorhynchus tshawytscha) prolactin cDNA probe. The sequence of this clone (ATPRL-5) was determined. Comparison of this sequence and other published sequences showed all the prolactin genes isolated to date are highly conserved. The expression of the prolactin mRNA from adult and juvenile salmon was studied after transfer between salinities. Expression varied in the predicted manner. Adult salmon transferred to fresh water showed large increases in the prolactin mRNA level compared to control fish (>600% increase after 72 h). Only a small difference was observed when smolts (juvenile salmon) were transferred to salt water.     

Plasma levels of insulin and liver glycogen contents in one- and two-year old Atlantic salmon (Salmo salar L.) during the period of parr-smolt transformation

Plasma levels of insulin were measured by specific radioimmunoassay in 1-year and 2-year old Atlantic salmon (Salmo salar) parr during the period of parr-smolt transformation. The two-year old fish were of two different categories; silvering pre-smolts and previously mature male parr. If insulin plays an important role in parr-smolt transformation and/or subsequent osmoregulatory changes it was expected that the pre-smolts would show a different insulin profile compared to the mature male parr and one-year old parr, both of which show impaired hypoosmoregulatory ability compared to smolts. Measurements were taken during two separate years. Between January and April both categories of two-year old fish had generally higher plasma levels of insulin compared to the non-smolting one-year old parr. In the pre-smolts insulin levels ranged from 4.0 to 7.9 ng ml⁻¹, and from 7.8 to 16.7 ng ml⁻¹ in 1990 and 1992 respectively, while in the previously mature males the same respective values were from 4.3 to 10.0 ng ml⁻¹, and from 6.6 to 24.1 ng ml⁻¹. In the two-year old fish, whether pre-smolts or mature males, plasma insulin levels peaked between 1–2 months before final smoltification, after which insulin titers declined sharply. In 1990, the 1-year old parr showed a dual peak in plasma insulin. Insulin first peaked in February (7.8 ng ml⁻¹), and then again in April–May (7.7 ng ml⁻¹), while in 1992 the 1-year old parr showed a number of smaller transient peaks (5–7 ng ml⁻¹) between March–May, followed by sharp elevation of insulin levels in June. Liver glycogen contents were at their highest (3.5–5.0 g 100 g⁻¹ I liver wet weight) in March in both 1-year and 2-year old fish. Glycogen levels were low during the later stages of parr-smolt transformation, before rising again in June in both the 1-year old and precociously mature parr, but not in the smolts.     

Characterization of growth hormone binding sites in the goldfish,Carassius auratus: effects of hypophysectomy and hormone injection

A recombinant carp growth hormone (rcGH) was used to develop for a GH radioreceptor binding assay in the goldfish (Carassius auratus). Specific binding of¹²⁵I-rcGH to goldfish liver membranes was a pH, time, temperature, and membrane protein dependent process. Scatchard and LIGAND analysis indicated a single class of high affinity and low capacity binding site, with an association constant (Ka) of 1.9×10¹⁰ M^–1 and a maximum binding capacity (B_max) of 9 fmol mg^–1 protein. Liver tissue displayed the highest¹²⁵I-rcGH binding of all the tissues examined. Displacement of¹²⁵I-rcGH with various unlabeled teleost and mammalian GHs and prolactins revealed that the goldfish hepatic binding site was highly specific for teleost GH. Intraperitoneal administration of 0.1, 1.0, and 10 g rcGH g^–1 body weight to hypophysectomized goldfish resulted in a 27, 52, and 68% decrease in total binding sites, respectively. Injection of a high dose of rat prolactin (rPRL) (5 g rPRL g^–1 body weight) also resulted in a 32% decrease in total binding sites. These results suggest that endogenous GH may have a role in the regulation of its own receptors in the goldfish.     

Mitochondrial enzyme and Na+, K+-ATPase activity,and ion regulation during parr-smolt transformation of Atlantic salmon (Salmon salar)

Atlantic salmon (Salmo salar) exposed to either simulated natural photoperiod (SNP) or continuous light (L24) were used to examine developmental changes in the presence and absence, respectively, of the parrsmolt transformation. Plasma osmolarity and ion concentrations were unaffected by photoperiod treatment. Gill Na⁺, K⁺-ATPase specific activity increased 150% between February and June in SNP fish and was low and unchanged in L24 fish. Kidney Na⁺, K⁺-ATPase specific activity varied within similar, narrow limits in both groups. Citrate synthase of liver, gill and kidney, expressed as specific activity or activity/g total body weight (relative activity), increased 25–60% between March and June in SNP fish. With the exception of kidney relative activity, citrate synthase activity declined to initial (March) levels by August. Liver, gill and kidney cytochrome c oxidase activity of the SNP group underwent similar though less marked changes. Liver, gill and kidney citrate synthase and cytochrome c oxidase activities of the L24 group remained relatively constant between March and August, and where significant differences occurred, they were lower than those of the SNP group. These results indicate that respiratory capacities of the liver, gill and kidney increase in smolls concurrent with preparatory osmoregulatory changes, and subsequently decline. The findings are consistent with a hypothesized transient increase in catabolic activity during the parr-smolt transformation that may be due to the metabolic demands of differentiation.     

Osmoregulatory ability and stress responses during freshwater adaptation of black porgy (Acanthopagrus schlegeli) treated with exogenous prolactin

The effects of ovine prolactin (oPRL) on osmoregulatory ability (electrolyte balance, plasma osmolality and activity of gill chloride cells and gill Na⁺/K⁺‐ATPase) and stress responses (plasma cortisol, glucose, aspartate aminotransferase: AST and alanine aminotransferase: ALT) were investigated in black porgy transferred to freshwater (FW). Fish in seawater (SW) were injected twice at a 24 h interval with oPRL (at 1, 3, or 5 μg g^–1 body weight) or vehicle (0.9% NaCl) and then transferred to FW. They were sampled 3 days after the transfer. With oPRL at 5 μg g^–1, levels of plasma Na⁺ and Cl^? and osmolality were significantly higher than in saline‐treated fish, whereas gill CCs number and Na⁺/K⁺‐ATPase activity were lower. Also, the 5 μg g^–1oPRL treatment led to significantly lower plasma cortisol levels than did saline treatment. However, there were no significant differences in plasma AST and ALT between groups. These results support the positive osmoregulatory role of PRL in black porgy during FW adaptation.     

Ammonia and urea excretion in the tidepool sculpin (Oligocottus maculosus): sites of excretion,effects of reduced salinity and mechanisms of urea transport

Tidepool sculpins live in a variable environment where water temperature, salinity, gas tensions, and pH can change considerably with the daily tide cycle. Tidepool sculpins are primarily ammoniotelic, with 8–17% of nitrogen wastes excreted as urea. The majority of net ammonia (J^net _amm; 85%) and urea (J^net _urea; 74%) excretion occurred across the gill, with the remainder excreted across the skin, the kidney, and/or gut. Acute (2h) exposure to 50% seawater significantly increased J^net _urea (2.8-fold), but reduced J^net _amm (3.5-fold). In fish exposed to 50% seawater for 1 week, J^net _urea returned to control values, but J^net _amm remained slightly depressed. Unidirectional urea influx (Jⁱⁿ _urea) and efflux (J^out _urea) were measured using¹⁴C-urea to determine if urea was excreted across the gills by simple diffusion or by a carrier-mediated mechanism. Jⁱⁿ _urea increased in a linear manner with increasing urea water levels (0–11 mmol N l^–1), while J^out _urea was independent of external urea concentrations. As well, J^net _urea and J^{out inurea} were not significantly different from one another, indicating the absence of back transport. Urea analogs and transport inhibitors added to the water did not have any consistent effect on unidirectional urea flux. These results demonstrate that ammonia and urea excretion rates and sites of excretion in tidepool sculpins are very similar to those found in other marine and freshwater teleosts. Urea and ammonia may play a role in osmoregulation as excretion rates and tissue levels were influenced by changes in water salinity. Finally, we found no evidence for a specific urea carrier; branchial urea excretion is likely dependent on simple diffusion.     

Osmoregulation in the mudskipper,Boleophthalmus boddaerti II. transepithelial potential and hormonal control

Boleophthalmus boddaerti submerged in 10%, 50% and 80% seawater (sw) for 7 days, had whole body transepithelial potentials (TEP) of 3.3, 18.3 and 22.9 mV, respectively. Hypophysectomy significantly decreased the TEP ofB. boddaerti and reversed the polarity of the TEP of the fish exposed to 10% sw.Hypophysectomy also significantly decreased the branchial Na⁺-K⁺ activated adenosine triphosphatase (Na⁺,K⁺-ATPase) activity but increased the activity of branchial HCO₃ ^–-Cl^– stimulated adenosine triphosphatase (HCO₃ ^–,Cl^–-ATPase) inB. boddaerti exposed to 10% sw. However, survival in 10% sw was not significantly impaired by hypophysectomy and no significant change in plasma osmolality and plasma Na⁺ and Cl^– concentrations was observed.Various doses of ovine-prolactin or salmon-prolactin were unable to restore the TEP of hypophysectomizedB. boddaerti in 10% sw to that of the sham-operated fish. However, cortisol increased TEP to a positive value in hypophysectomizedB. boddaerti, though it was still lower than the sham-operated control. Cortisol treatment also affected the plasma osmolality, plasma Na⁺ and Cl^– contents and branchial Na⁺,K⁺-ATPase and HCO₃ ^–,Cl^–-ATPase activities. Overall, the hormonal control of osmoregulation inB. boddaerti appeared to differ from that of other teleosts.     

Insulin-like growth factor I (IGF-I) mRNA expression in coho salmon,Oncorhynchus kisutch: Tissue distribution and effects of growth hormone/prolactin family proteins

To examine the hormonal and nutritional regulation of insulin-like growth factor I (IGF-I) mRNA expression, a sequence-specific solution hybridization/RNase protection assay for coho salmon IGF-I mRNA was developed. This assay is both rapid and sensitive and has low inter- (less than 15%) and intra-assay variations (less than 5%). Using this assay, the tissue distribution of IGF-I mRNA and effects of growth hormone (GH), prolactin (PRL) and somatolactin (SL) on hepatic IGF-I mRNA expression in coho salmon were examined in vivo. Liver had the highest IGF-I mRNA level of 16 pg/μg DNA. Significant amounts of IGF-I mRNA were also found in all other tissues examined (intestine 4.1, kidney 3.8, gill arch 2.4, brain 2.4, ovary 2.3, muscle 2.1, spleen 1.7 and fat 1.1 pg/μg DNA). Injection of coho salmon GH at doses of 0.1 and 1 μg/g body weight significantly increased the hepatic IGF-I mRNA levels in a dose-dependent manner. Injection of coho salmon SL, a recently discovered member of the GH/PRL family, stimulated the IGF-I mRNA expression at the higher dose (1 μg/g), whereas coho salmon PRL had no effect at either dose. Concentration-dependent stimulation by coho salmon GH was also obtained in vitro in primary culture of salmon hepatocytes in concentrations ranging from 0.01 to 1 μg/ml. These results indicate that IGF-I mRNA expression occurs in a variety of tissues in coho salmon, and that at least the hepatic expression is under the regulation of GH and possibly other hormones. The sequence-specific assay established in the present study can be used for accurate quantitation of IGF-I mRNA in salmonid species, and can contribute to a better understanding of the physiology of IGF-I in salmonids.

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Résumé Afin d'étudier les régulations homronales et nutritionnelles de l'expression des ARNm de l'IGF-I (insulin-like growth factor I), un dosage spécifique par hybridation en solution des ARNm d'IGF-I de saumon coho et protégé des RNases, a été développé. Ce dosage, à la fois rapide et sensible, présente un faible coefficient de variation inter- (< 15%) et intra- (< 5%) dosage. L'étude de la distribution tissulaire des ARNm de l'IGF-I et des effets de l'hormone de croissance (GH), de la prolactine (Prl) et de la somatolactine (SI) sur l'expression hépatique des ARNm de l'IGF-I, a été entreprise in vivo chez le saumon coho en utilisant ce dosage. Le foie présente les plus grandes quantités d'ARNm d'IGF-I (16 pg/μg d'ADN). Des quantités significatives d'ARNm d'IGF-I ont été également détectées dans tous les autres tissus étudiés (intestin 4,1; rein 3,8; branchie 2,4; ovaire 2,3; muscle 2,1; rate 1,7 et graisse 1,1 pg/μg d'ADN). L'injection à des saumons coho, de GH à des doses de 0,1 et 1 μg/g de poids vif, augmente significativement et de manière dose dépendante les niveaux hépatiques d'ARNm d'IGF-I. L'injection de SI de saumon coho, un membre récemment découvert de la famille GH/Prl, stimule avec la plus haute dose utilisée, l'expression des ARNm d'IGF-I alors que la Prl n'a aucun effet. La GH augmente de manière dose dépendante (0,01–1 μg/ml) l'expression in vitro des ARNm d'IGF-I par des ARNm d'IGF-I par des hépatocytes de saumon coho en culture. Ces résultats indiquent que, chez le saumon coho, l'expression des ARNm d'IGF-I est présente dans le nombreaux tissus et que, l'expression hépatique est, au moins en partie, régulée par la GH et peut-être par d'autres hormones. Le dosage par séquence spécifique mise au point dans le présent travail, peut-être utilisé pour la quantification précise des ARNm, d'IGF-I de salmonidés et devrait permettre une meilleure connaissance de la physiologie de L'IGF-I chez les salmonidés.

     

Changes in plasma prolactin and growth hormone concentrations during freshwater adaptation of juvenile chum salmon (Oncorhynchus keta) reared in seawater for a prolonged period

Freshwater adaptability of chum salmon was examined in juvenile fish reared in seawater for 4 months. The fish, weighing about 40g, were transferred directly to fresh water in October, when their cohorts are migrating in the North Pacific Ocean. Plasma sodium concentration decreased from 167 mM in seawater to about 130 mM during the first 24h, and increased gradually during 2–7 days after the transfer. No immunoreactive prolactin (PRL) was detected in the plasma of the seawater-adapted fish nor during the first 24h in fresh water. Significant levels of PRL were detected after 2–3 days. The maximal level (2.6 ng/ml) was observed after 5 days and became undetectable again after 7 days; no significant correlation was seen between the changes in plasma sodium and PRL levels during the transfer. Plasma growth hormone levels were relatively constant, except for a significant decrease 12h after the transfer. Although plasma thyroxine levels were highly variable during the experiment, a significant decrease and an increase were observed 12h and 5 days after the transfer, respectively. The present study indicates that juvenile chum salmon retain hyperosmoregulatory ability even after prolonged rearing in seawater. Examination of turnover rates, rather than changes in plasma levels, seems to be essential to clarify the osmoregulatory roles of the hormones.     

Morphological characterization and notes on the life cycle of a newly discovered variant of Loma salmonae (Putz, Hoffman & Dunbar) from a natural infection of chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Two variants of Loma salmonae occur in net-pen reared chinook salmon, Oncorhynchus tshawytscha. The typical variant (OA) has a host specificity for salmonids of the genus Oncorhynchus whereas the atypical variant (SV) has a host specificity for brook trout, Salvelinus fontinalis, and in this study, the ultrastructure of the two are compared. In fish at 8 weeks post-exposure xenomas of the SV variant have a very high proportion of mature spores compared with other developmental stages, while in xenomas of the OA variant there are fewer spores and many other developmental stages. Spores of the SV variant had up to 20 turns of their polar tube whereas those of the OA variant only had 17. Furthermore, the spores of the SV variant were significantly larger than those of the OA variant. The sporophorous vesicle for both variants appears to form around a sporogonial plasmodia, which results in many spores developing within the vesicle.     

Effects of the aromatase inhibitor Fadrozole on plasma sex steroid secretion and oocyte maturation in female coho salmon (Oncorhynchus kisutch) during vitellogenesis

17-estradiol, 17-20-dihydroxy-4-pregnen-3-one (17-20-P), and testosterone levels were measured in plasma samples obtained from vitellogenic coho salmon (Oncorhynchus kisutch) before and 32 days after injection of the aromatase inhibitor Fadrozole (AI). Plasma 17-estradiol levels decreased significantly 6 h after injection in all AI treated fish. The higher the dose the longer the maintenance of low plasma 17-estradiol levels. Inversely, plasma 17-20-P increased significantly 6 h after injection in all AI treated fish, and the higher the dose the longer the maintenance of high plasma 17-20-P levels. At 48 h after injection plasma testosterone levels were significantly higher in the AI treated groups. The oocyte maturation index showed that multiple injections with AI retarded oocyte development. Besides, oocyte diameter and GSI were lower in the same group, which presented high incidence of atresia of vitellogenic oocytes. The ovarian follicles and brain of the fish which received multiple injections secreted less 17-estradiol, in vitro. These findings suggest that aromatase inhibitors such as Fadrozole may have a potential as a tool to regulate sexual development in salmon.     

Antioxidant Properties and the Preservative Effect of Whole Radish Extract on Quality of Deccan Mahseer (Tor khudree) Steaks during Chilled Storage

ABSTRACT

The effect of dip treatment with solvent-free whole radish extract (WRE) on quality characteristics of Deccan mahseer steaks was evaluated during the chilled storage. In-vitro antioxidant activities of the extract were evaluated based on total phenolic and flavonoid contents, DPPH radical scavenging activity, and metal chelating ability prior to the dip treatment. The quality parameters, including total volatile base nitrogen (TVB-N), trimethylamine nitrogen (TMA-N), and free fatty acid (FFA), were significantly (p < .05) reduced in WRE treated steaks compared to the control (CT) steaks. WRE treatment of fish steaks significantly controlled the lipid oxidation parameters of thiobarbituric acid reactive substances (TBARS) and peroxide value (PV). Total plate count (TPC) of CT sample was higher than the treated sample and remained within the limit of 7 log₁₀ cfu/g at the end of storage. As per the sensory analysis, shelf life of Deccan mahseer was determined to be 15 days for WRE treated steaks and 9 days for control steaks during chill storage. Based on the results, it can be concluded that WRE treatment can limit the progress of fish spoilage bacteria in fish steaks and can be used as a substitute for synthetic additives.     

Uptake and clearance of exogenous estradiol-17β and testosterone during the early development of coho salmon (Oncorhynchus kisutch), including eggs,alevins and fry

The uptake and clearance of estradiol-17β (E₂) and testosterone (T) were examined during the initial stages of development of coho salmon (Oncorhynchus kisutch), including eyed-eggs, newly hatched alevins and first feeding fry. Radiolabeled steroids were administered through the water in tracer amounts with or without their nonradioactive form at 400 μg l⁻¹. Regardless of developmental stage, saturation levels were invariably attained earlier for T than for E₂, thus resulting in a higher incorporation of E₂. However, both steroids had similar clearance patterns. Uptake and clearance was clearly stage-dependent, being fastest in fry, intermediate in alevins and slowest in eggs. Furthermore, combined uptake and clearance patterns showed that exposure to steroid was also higher for E₂ than for T and stage-dependent, but always markedly highest in alevins. Subsequently, based on the observed elimination of the estrogen, a double immersion in E₂ at 400 μg 1⁻¹, administered 2 days apart to maximize exposure during the alevin stage, was assayed for its effect on sex reversal and found to induce the production of 100% females. We suggest that the yolk, which is present in substantial amounts during the initial stages of development in salmonids, can retain the exogenously administered liposoluble steroids, thus providing developing embryos with an extended supply of, and exposure to, these steroids well after the treatment is finished. Together, these findings help to explain the previously observed high effectiveness of sex steroids administered during early development in regulating gonadal differentiation in salmonids, the higher effectiveness of E₂ compared to T, and clarify the localization of the most sensitive period to the action of exogenous steroids at the alevin stage in the coho salmon.     

Carbohydrate and lipid digestibility of animal and vegetal ingredients and diets for the pre-adult redclaw crayfish, Cherax quadricarinatus (von Martens)

In vivo carbohydrate and lipid digestibility of four animal [sardine meals 67% and 58% crude protein (CP), squid meal and red crab meal] and three vegetal (soy paste, textured wheat and sorghum meal) ingredients and diets were evaluated in experimental diets for pre-adult redclaw crayfish, Cherax quadricarinatus . A reference and seven experimental diets were formulated, including 14.5% of each ingredient in the reference diet. A single factor, completely randomized experimental design with five replicates per treatment was done. Experimental organisms were pre-adult redclaw of 10±0.8 g. The best carbohydrate digestibilities were recorded for some vegetal ingredients such as sorghum and textured wheat (93.6% and 83.9%) and the corresponding diets (90.9% and 90.8%). For animal ingredients, carbohydrate digestibilities were very poor (from 12.3% to 41.1%), and the inclusion of these ingredients diminished the digestibility of the corresponding experimental diets as compared with the reference diet (86.3–89.2% vs. 89.9%). The highest lipid digestibility corresponded to red crab meal (97.5%). Textured wheat and soy paste meal also had excellent lipid digestibility (96.4% and 95.1%). The same tendency was found for the corresponding diets. The lowest percentages were obtained with 58% crude protein sardine meal (32.9%) and its diet (86.2%).