Mature Female Rainbow Trout Research Articles

Long-term implantation of acoustic transmitters induces chronic inflammatory cytokine expression in adult rainbow trout (Oncorhynchus mykiss)

Telemetry transmitters are frequently used in studies of wild fish migration and behavior. Although the effects of surgically implanted transmitters on survival, tag retention, healing and growth have been studied, there has been little research regarding the potential immune response induced by these transmitters. In the current study, mature rainbow trout received either surgical implantation of an acoustic transmitter or a sham surgical procedure. These fish were then sampled over a 10-week period so that pro-inflammatory cytokine expression in the spleen, peritoneal cavity lymphocytes and muscle at the surgical site could be analyzed. There were no significant differences in transcript expression for the spleen and muscle tissue between fish that had a transmitter and those that received the surgical procedure alone. However, transmitter presence significantly increased the expression of IL-6, IL-1β and TNFα in the peritoneal cells at 10 weeks indicating that tagged fish may be coping with chronic inflammation. Furthermore, tagged male fish had a higher inflammatory response in 10-week peritoneal lavage samples when compared to their tagged mature female counterparts, providing some evidence that mature female rainbow trout may have suppressed immune function when sexually mature. Externally, fish appeared to heal at similar rates regardless of the presence or absence of the transmitter, but the tag itself was prone to encapsulation and adhesion to the body wall and/or surgical site. This suggests that fish tagged with large intraperitoneal implants may not behave similarly to their wild counterparts. This research could aid in the development of improved telemetry tags that are more biocompatible, economical and better able to track fish behavior/movement.

Mode of the Intra-ovum Infection of Flavobacterium psychrophilum in Salmonid Eggs

The mode of intra-ovum infection by Flavobacterium psychrophilum, which causes bacterial cold-water disease and rainbow trout fry syndrome, was investigated in eggs of rainbow trout Oncorhynchus mykiss. When newly spawned unfertilized eggs were immersion-challenged with F. psychrophilum at concentrations of 107 CFU/mL or higher and subsequently inseminated and water-hardened, the bacteria were detected in the egg contents. The infection rate in eggs was related to the bacterial concentration in a dose-dependent manner. When mature female rainbow trout were intraperitoneally injected with F. psychrophilum (3.3 × 109 CFU/fish) 5-9 days prior to ovulation, intra-ovum infection was found in eggs spawned from the fish showing heavy contamination of the bacterium in the ovarian fluid (> 106 CFU/mL). These results indicate that F. psychrophilum can contaminate the surface of eggs in ovarian fluid and enter eggs during water-hardening. Live bacterial counts within experimentally infected eggs and immuno-staining observations on the eggs suggested that F. psychrophilum passively entered into the eggs (< 10 CFU/egg) and subsequently grew to over 107 CFU/egg in the perivitelline space by the eyed egg stage. Multiplication of the bacterium in the perivitelline space did not affect the survival of eggs.

Messenger RNA stockpile of cyclin B, insulin-like growth factor I, insulin-like growth factor II, insulin-like growth factor receptor Ib, and p53 in the rainbow trout oocyte in relation with developmental competence.

In the present study, correlations between the oocyte messenger RNA (mRNA) stockpile of Cyclin B, insulin-like growth factor I (IGF-I), insulin-like growth factor (IGF-II), insulin-like growth factor receptor Ib (IGFR Ib), and p53 transcripts and the developmental competence of the oocyte were studied. For this purpose, post-ovulatory ageing was used as a tool to generate oocytes of varying developmental competence. Mature female rainbow trout were held at 12 degrees C and periodically checked for ovulation. Oocytes were collected from each female at ovulation and 5, 14, 21 days later. For each collected egg batch, the abundance of several mRNAs in the oocyte was analyzed by real-time PCR and embryo development was monitored after fertilization. Egg quality was estimated not only through embryonic survival but also by studying the occurrence of specific morphological abnormalities. The present study showed that oocyte post-ovulatory ageing was associated with variations of the relative abundance of several studied transcripts within the oocyte. In addition, the abundance of specific mRNAs could be correlated with either the embryonic survival or the occurrence of malformations. Thus, the abundance of IGFR Ib and Cyclin B transcripts in the oocyte was correlated with the occurrence of morphological abnormalities observed at yolk-sac resorption (negatively for IGFR Ib and positively for Cyclin B), while the maternal stockpile of IGF-I, IGF-II, and IGFR Ib mRNAs was positively correlated with embryonic survival.

Effects of sex steroids, sex, and sexual maturity on cortisol production: an in vitro comparison of chinook salmon and rainbow trout interrenals

Sex steroids appear to be responsible for hyperactivation of the hypothalamus–pituitary–interrenal (HPI) axis that occurs in mature semelparous Pacific salmon as a prelude to post-spawning (programmed) death. This study was undertaken to examine the direct effects of sex steroids on interrenal activity of semelparous (chinook salmon) and iteroparous (rainbow trout) salmonids using an in vitro incubation system. In addition, phenotypic sex differences in cortisol production by interrenals of sexually mature (spawning) rainbow trout and chinook salmon were investigated. Interrenal tissue from juvenile and sexually mature chinook salmon and rainbow trout was incubated for 48 h in culture medium containing either no steroid (controls), 1 μM estradiol (E2) or 1 μM 11-ketotestosterone (11-KT). This tissue was then challenged for 3 h with either pregnenolone, dibutyryladenosine 3 ′:5 ′-cyclic monophosphate (dbcAMP) or forskolin, or synthetic human adrenocorticotropic hormone (ACTH 1–24). Sex differences in in vitro interrenal cortisol production were assessed using separate tissue pools challenged with the same agents. Cortisol in media was measured by radioimmunoassay. E2 suppressed the ability of juvenile chinook salmon interrenals to utilize pregnenolone as substrate for cortisol synthesis. In mature female chinook salmon the suppressive effect of E2 was less pronounced, but was observed as a reduced response of interrenals to both pregnenolone and dbcAMP. E2 did not affect ACTH 1–24 stimulated cortisol production. Immature and mature rainbow trout interrenals were both relatively insensitive to E2. 11-KT did not affect cortisol production by juvenile chinook salmon and juvenile or mature rainbow trout, and had only minor effects in male and female spawning chinook salmon. In mature chinook salmon and rainbow trout, the interrenals of females were more responsive to ACTH stimulation and showed a greater utilization of pregnenolone as a substrate than interrenals of males. Mature female rainbow trout were also more responsive to dbcAMP stimulation than males. The results of this study suggest that the onset of sexual maturation and gonadal steroid production may contribute to sexually dimorphic cortisol responses in vitro.

Male priming pheromone is present in bile, as well as urine, of female rainbow trout

The bile of sexually mature female rainbow trout Oncorhynchus mykiss has pheromonal activity which causes a significant increase in concentrations of 17,20β-dihydroxy-4-pregnen-3-one in the plasma of males. Bile from male trout is inactive. The activity in the female bile binds to octadecylsilane and can be eluted with methanol. The synthetic bile acids, taurocholic acid and taurolithocholic acid, are inactive.

Effect of holding temperature on ovulation, egg fertility, plasma levels of reproductive hormones and in vitro ovarian steroidogenesis in the rainbow trout Oncorhynchus mykiss

Sexually mature female rainbow trout were held at temperatures ranging from 9–21 °C for up to 3 months prior to the natural time of ovulation, in experiments conducted over three different spawning seasons. The majority of fish held at 9 and 12 °C ovulated, variable numbers ovulated at 15 and 18 °C and only one fish ovulated at 21 °C. Egg production was similar at 9, 12 and 15 °C, significantly lower at 18 °C and near zero at 21 °C. Egg survival to the eyed stage after incubation at 11 °C was similar at 9, 12 and 15 °C, and nil at 18 and 21 °C. Histological examination of oocytes from fish held at 12, 15 or 18 °C for 1 or 2 months showed no evidence of gonadal atresia. Plasma levels of gonadotropin (GtH) were measured in samples taken 1, 2 and 3 months after introduction to temperatures of 9, 12, 15, 18 or 21 °C, and showed no differences between temperatures at any time. Plasma levels of testosterone (T) and 17β-oestradiol (E 2) were similarly unaffected. Repeat measurement of T and E 2 in another spawning season also showed that holding temperature had no effect on plasma steroid levels. In contrast, in vitro basal steroidogenesis by isolated ovarian follicles was generally lower at 18 °C than at 12 or 15 °C. Follicles from fish held at 18 °C for 2 months did not retain responsiveness to stimulation with steroid precursors or GtH, whereas those from fish held at 12 and 15 °C did. The results indicate that elevated autumn holding temperatures have a deleterious effect on ovulation, egg production and fertility but have equivocal effects on endocrine parameters associated with vitellogenesis. This suggests that the effects are exercised on processes associated with final maturation and ovulation rather than vitellogenesis.

Urine of reproductively mature female rainbow trout, Oncorhynchus mykiss (Walbaum), contains a priming pheromone which enhances plasma levels of sex steroids and gonadotrophin II in males

Urine of reproductively mature female rainbow trout was shown to contain a priming pheromone which raised the levels of 17a,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β‐P), testosterone and gonadotrophin II in the blood plasma of reproductively mature male rainbow trout. Milt volumes, however, were unaffected.Because it had been established in a previous study that the sulphated form of 17,20β‐P is abundant in the urine of spawning rainbow trout, synthetic 17a,20β‐dihydroxy‐4‐pregnen‐3‐one 20‐sulphate was also tested for pheromonal activity. It was found to have only a smalt and inconsistent priming effect on steroid levels and did not alter the orientation or spawning activity of males.It was also shown that, in the majority of experiments, there was a significant drop, over the course of 24 h, in the levels of 17,20β‐P and testosterone in the control groups of males.

Urine of reproductively mature female rainbow trout, Oncorhynchus mykiss (Walbaum), contains a priming pheromone which enhances plasma levels of sex steroids and gonadotrophin II in males

Urine of reproductively mature female rainbow trout, Oncorhynchus mykiss (Walbaum), contains a priming pheromone which enhances plasma levels of sex steroids and gonadotrophin II in males

Absorption and blood clearance of labelled carotenoids ([ 14C]astaxanthin, [ 3H]Canthaxanthin and [ 3H]zeaxanthin) in mature female rainbow trout ( Oncorhynchus mykiss)

1. 1. Using one force-fed meal, eight mature female rainbow trout received [ 14C]astaxanthin ([ 14C]Ax) with [ 3H]canthaxanthin ([ 3H]Cx; N = 3) or with [ 3H]zeaxanthin ([ 3H]Zx; N = 5). 2. 2. Approximately 200 μl of blood were collected via caudal puncture every 24 hr for 4 days. After 96 hr, the fish were killed and pyloric caeca (P.C.) from the duodenal intestine (D.I.) section, ileal intestine (I.I.), and posterior intestine (P.I.) were dissected out. 3. 3. In the blood, Ax levels were higher than Cx followed by Zx levels. 4. 4. This corresponds to their respective absorption by the trout as was confirmed by their relative concentrations in P.C., I.I. and P.I. 5. 5. However, blood clearance was similar for all three compounds. [ 14C]Phoenicoxanthin ([ 14C]Px) was detected as a reduced metabolite of [ 14C]Ax in all gut sections.

17 alpha,20 beta-dihydroxy-4-pregnen-3-one 20-sulphate is a potent odorant in precocious male Atlantic salmon (Salmo salar L.) parr which have been pre-exposed to the urine of ovulated females.

Electrophysiological recordings from the olfactory epithelium have shown that 17 alpha,20 beta-dihydroxy-4-pregnen-3-one 20-sulphate (17,20 beta-P-sulphate; a conjugate of the oocyte-maturation-inducing steroid in teleosts) is a potent odorant in precocious male Atlantic salmon (Salmo salar L.) parr. However, the olfactory epithelium of these fish only appeared to be responsive to the steroid after stimulation with the urine of ovulated female Atlantic salmon. Immature fish did not respond at any time. Stimulation with urine from immature and precocious male Atlantic salmon parr did not make the olfactory epithelium of precocious male salmon parr responsive to the steroid. 17,20 beta-P-sulphate was found in the urines of ovulated females, precocious male parr and mature male Atlantic salmon. The findings are discussed in relation to the possible role of 17,20 beta-P-sulphate in the physiology of Atlantic salmon.

Comparative accumulations of labelled carotenoids ( 14C-astaxanthin, 3H-canthaxanthin and 3H-zeaxanthin) and their metabolic conversions in mature female rainbow trout ( Oncorhynchus mykiss)

1. 1. One force-fed meal containing labelled 14C-astaxanthin ( 14C-Ax) and 3H-canthaxanthin ( 3H-Cx) or 3H-zeaxanthin ( 3H-Zx) was given to eight mature female rainbow trout. Ninety-six hours after the test meal ingestion, trout were killed and liver, skin, muscle and ovarries were dissected out. 2. 2. Ax accumulated slightly more in muscle than Cx but in all tissues Ax and Cx were very significantly more concentrated than Zx. 3. 3. 3H-Zx metabolites were found only in the liver, whereas 14C-phoenicoxanthin was the only metabolic pigment from 14C-Ax detected and was found in all investigated tissues. 4. 4. 3H-Ax was found in the liver of all trout indicating that 3H-Cx and 3H-Zx were Ax precursors, and that salmonids probably possess carotenoid oxidative pathways unknown until now. 5. 5. Labelled retinol 1 and retinol 2 were detected only in the liver and 3H-Zx was largely the predominant precursor of these two vitamin A forms.

Serum phosphoprotein phosphorus and calcium levels as reproductive indicators of vitellogenin in highly vitellogenic mature female and estradiol-injected immature rainbow trout (Salmo gairdneri)

A linear relationship exists between increasing levels of the indirect indicators serum total phosphoprotein phosphorus (TPP), alkali-labile phosphoprotein phosphorus (ALPP), and total calcium (Ca) and increasing levels of serum vitellogenin (Vg) in mature female rainbow trout (Salmo gairdneri) during active vitellogenesis. A similar result was observed with TPP, Ca, and Vg in immature rainbow trout injected with 17β-estradiol (E2). Although TPP, ALPP, and Ca could be utilized to distinguish vitellogenic from nonvitellogenic fish, the phosphoprotein phosphorus measures TPP and ALPP emerged as the most reliable indirect indicators of serum Vg levels. Linear regression equations developed from the data allow the estimation of Vg levels from TPP or Ca values for both highly vitellogenic mature female and E2-injected immature rainbow trout when a direct assay for vitellogenin is not available.

Comparative studies on immunochemical properties of female-specific serum protein and egg yolk proteins in rainbow trout ( Salmo gairdneri)

1. 1. Female-specific serum protein (FS) and egg yolk proteins of mature female rainbow trout ( Salmo gairdneri) were studied comparatively with reference to their immunological and some physicochemical properties. 2. 2. FS was considered to be composed of two egg proteins, E1 and E2, which were isolated from the egg yolk by gel filtration. 3. 3. The molecular weights of FS, E1 and E2 were estimated by gel filtration to be approx 600,000, 300,000 and 35,000, respectively. 4. 4. The analysis with sodium dodecyl sulphate electrophoresis indicated that E1 consisted of two subunits with molecular weights of 90,000 and 15,000, and E2 was estimated to be a dimer of a molecule of 15,000. 5. 5. Male and immature female trout were injected with estradiol-17β, and the production of proteins with the same antigenicity with FS was demonstrated.