Francisco Estay

Diploid chromosome number variations and sex chromosome polymorphism in five cultured strains of rainbow trout (Oncorhynchus mykiss)

Abstract This work reveals the chromosomal characteristics of the five cultured strains of rainbow trout, Oncorhynchus mykiss. The five strains—Americana, Donaldson, Cofradex, Steelhead, and Kamloops—are those commonly used in the Chilean salmon farming industry. Chromosome characterization involved the determination of diploid chromosome number (2n), chromosome arm number (NF) and sex chromosome of individuals by Hoechst 33258/Actinomicyn D (H/AmD) fluorescent stain. Considering all of the strains studied, the 2n ranged from 58 to 63 chromosomes. All of the karyotypes had NF=104. Within this range of variation, the strains exhibited low (Americana, 2n=59–60; Steelhead and Kamloops, 2n=58–61), intermediate (Cofradex, 2n=59–62) or high chromosome numbers (Donaldson, 2n=61–63). In strains with the most extreme diploid chromosome numbers, the most frequent 2n corresponded to 59 and 61 chromosomes. Sex chromosome determination revealed that 24.5% of specimens of both sexes, presented an unexpected sex chromosome. In males, “XX” specimens were observed, whereas in females, “XY” or “XXX” individuals were recorded. The subtelocentric (st) morphology and centromeric H/AmD banding pattern of the additional “X” chromosome in “XX males” and “XXX females” is similar to that observed in the regular X chromosome. The chromosome number variation in the strains studied is consistent with the Robertsonian-type polymorphism described for rainbow trout. The presence of different chromosome numbers among strains, could reflect the chromosome differences existing within ancestral trout populations, or the presence of a certain degree of mixing with other populations of different geographical origin. The discovery of specimens with an unexpected sex chromosome is suggestive of an incomplete differentiation of the sex chromosome pair in the rainbow trout.

Physiological factors affecting triploid production in rainbow trout, Oncorhynchus mykiss

The influence of three physiological factors related to triploid production was examined for rainbow trout. Individual spawnings of 46 females were used to perform triploid production experiments from 1989 to 1991, with various water temperatures (6–13.8°C) at stripping and egg incubation. The percentage of triploids was similar for a heat shock of 26.5°C for 15 min applied 15 or 25 min after fertilization (73.4±5.6% vs 78.6±4.5%). A tendency to a higher percentage of triploids (85.9±5.7%) was observed for water temperatures of 6–8.0°C at stripping and incubation, compared to at higher water temperatures of 12.1–14°C (63.0±8.4%). Analysis of variance indicated an effect of four categories of water temperature (6–8, 8.1–10, 10.1–12, 12.1–14°C) on triploid product at P = 0.14. Regression analysis confirmed these as significant (r = −0.36; P < 0.02). A significant increase in percentage of triploids was observed when eggs remained 2, 6 and 10 days in the body cavity. The mean % triploidy was 46.1, 54.7 and 76.8, respectively. Similar results were observed for survival of the eggs.

GAMETOGENESIS AND SEX STEROID PROFILES IN CULTURED COHO SALMON (ONCORHYNCHUS KISUTCH, WALBAUM)

The gametogenesis of a 2-year-old coho salmon broodstock population cultured in a fish farm in southern Chile was studied. Gonadosomatic index (GSI), microscopic gonadal traits, and serum levels of estradiol-17β(E2), testosterone, and 17α,20β-dihydroxy-4-pregnene-3-one (17,20P) in both sexes were recorded beginning 9 months before spawning in bimonthly samplings. Maximum GSI means were reached during May, the month of spawning, with 16.8 ± 4.1% for females and 8.4 ± 0.8% for males, both values within the range described in the literature. GSI in males, however, was triple that of females during January, showing a faster rate of gonadal growth in males in early summer. Gonadal microscopy for both sexes showed stages corresponding to those described by different authors for other salmonids such as rainbow trout. The secondary vitellogenesis period was 4 to 5 months and corresponded with the short vitellogenesis model described in rainbow trout for broodstocks maturing at 2 years of age. The serum profiles of sex steroids in both sexes are consistent with those described in coho salmon and other salmonid species. In females, E2 and 17,20P show opposite profiles, reaching their maximum levels (E2: 45.13 ± 11.3 ng/ml; 17,20P: 24.47 ± 7.34 ng/ml) during vitellogenesis (March) and ovulation (May), respectively. In both sexes, testosterone concentration shows maximum levels in May (females: 61.68 ± 15.75 ng/ml; males: 107.8 ± 11.6 ng/ml), suggesting the physiological importance of this hormone during maturation, either directly or as a substrate for the synthesis of other hormones. In males, the maximum level of 17,20P (22.33 ± 4.5 ng/ml) also occurs in May during total spermiation, which confirms its role in semen production and semen fluid regulation as described in the literature about this hormone in salmonid males. On the basis of the data obtained, a reproductive pattern is proposed for 2-year-old salmon cultured in southern Chile. J. Exp. Zool. 280:429–438, 1998.

Analysis of Reproductive Performance of Rainbow Trout in a Hatchery in Chile

Abstract Reproductive variables of 986 female rainbow trout (Oncorhynchus mykiss) spawned during 1990 in a hatchery in central Chile were evaluated. Data were recorded on individual females. Fish were spawned over a 9-month period, from March to November. The data indicated the coexistence of different strains of fish with different spawning times. There was a direct relationship between body weight and total fecundity (r = 0.71; P < 0.001, n = 905). The correlation between body weight and egg diameter was low (r = 0.16; P < 0.001; N = 890). The correlation between body weight and relative fecundity was not only low, but slightly negative (r = -0.14; P < 0.001; N = 906). There was a high correlation between fertilization rate and survival of the embryo to the eyed stage (r = 0.75; P < 0.001; N = 903). Embryo survival to the eyed stage appeared to be closely related to incubation temperature, with highest yields obtained during months that average water temperature was 8°C or lower. Egg diameter was not po...

Analysis of the association between spawning time QTL markers and the biannual spawning behavior in rainbow trout (Oncorhynchus mykiss)

The rainbow trout is a salmonid fish that occasionally exhibits broodstocks with biannual spawning behavior, a phenomenon known as a double annual reproductive cycle (DARC). Spawning time quantitative trait loci (SPT-QTLs) affect the time of the year that female rainbow trout spawn and may influence expression of the DARC trait. In this study, microsatellite markers linked and unlinked to SPT-QTLs were genotyped to investigate the underlying genetics of this trait. SPT-QTLs influenced the DARC trait since in two case-control comparisons three linked markers (OmyFGT12TUF, One3ASC and One19ASC) had significant levels of allelic frequency differentiation and marker-character association. Furthermore, alleles of One3ASC and One19ASC had significantly higher frequencies in populations that carried the DARC trait.

Reproductive Performance of Cultured Female Coho Salmon in Chile

Abstract Data on reproductive traits from 1,229 mature 2-year-old female coho salmon Oncorhynchus kisutch were collected during 2 years at four salmon farms in southern Chile. Spawning periods were similar in 1993 and 1994 (39 and 41 d, respectively). The spawning period of May–June, corresponded to the full reproductive period in the northern hemisphere. The mean weight of mature females (about 4 kg) was almost double the weight reported in the northern hemisphere for 2-year-old maturing females. The pigmented eyed stage was reached approximately 270 accumulated temperature units (ATU days × °C above 0°C after fertilization. Averages for total fecundity (3,802 ± 956 eggs/female, mean ± SD; N = 1, 188), relative fecundity (986 ± 274 eggs/ kg; N = 1,170), and egg diameter (7.11 ± 0.51 mm; N = 1,185) were higher than corresponding values reported for coho salmon hatchery stocks in the northern hemisphere. Survival to the eyedegg stage averaged 74.3 ± 24.2% (N = 1,147). Correlations of female body weight wit...

Comparison of Oogenesis and Sex Steroid Profiles between Twice and Once Annually Spawning of Rainbow Trout Females (Oncorhynchus mykiss)

This study compares the gonadosomatic index (GSI), oocyte growth (OG), gonadal histology, and plasma level concentrations of sex hormones (estradiol-17β (E2) and vitellogenin (V)) of twice-spawning (T-SP) and once-spawning (O-SP) females of rainbow trout throughout the additional and the normal reproductive cycle, respectively. In T-SP, the GSI values rapidly increase from May to November, in contrast to O-SP, which showed low and constant GSI values (1.19 to 14.5 and 1.19 to 0.63, resp.). T-SP exhibited a marked increase of OG in the same period, reaching a maximum diameter of 4,900 ± 141.42 μm, in contrast to O-SP, which presented a slow OG. The gonadal histology of T-SP agreed with the general pattern of ovogenesis observed for O-SP (vitellogenesis, ovulation, and recrudescence); however, this process was nonsynchronous between the two breeder groups. Plasma steroid levels showed significant variation during oogenesis, which agreed with the GSI, OG, and gonadal histology patterns. The level of E2 increased to a maximum value of 26.2 ng/mL and 36.0 ng/mL in O-SP and T-SP, respectively, one or two months before the spawning event where vitellogenesis was fully active. The V concentrations followed a pattern similar to those of E2.

Skin Color Characterization in Rainbow Trout by Use of Computer-Based Image Analysis

Abstract Back, flank (reddish band along the lateral line and below the lateral line), and belly regions of cultured rainbow trout Oncorhynchus mykiss were characterized in terms of skin coloration, spottiness, and darkness by using computer-based image analysis as an approach to separate fish into desirable back color categories for market and export. Three highly represented colors were observed on the back (mean ± SE percentage of area covered by the given color): blue or sky-blue, 18.0 ± 1.8%; yellow, 13.4 ± 1.5%; and green, 66.1 ± 2.0%. Individuals with a high frequency of these colors on the back (at least 50% of area covered by a given color) were reclassified into groups exhibiting a yellowish back color (YB), a bluish back color (BB), or a greenish back color (GB) to determine whether the BB group presented differences in various skin color variables when compared with the other back color groups; an undefined back color (UB) group (fish for which all colors had less than 50% coverage) was also u...

Skin Spotting Variation Associated with Biometric and Reproductive Parameters in Naturalized Populations of Rainbow Trout, Oncorhynchus mykiss, from Southern Chile

RESEARCH ARTICLE Skin Spotting Variation Associated with Biometric and Reproductive Parameters in Naturalized Populations of Rainbow Trout, Oncorhynchus mykiss, from Southern Chile Nelson Colihueque, Francisco Javier Estay and Miguel Yáñez Departamento de Ciencias Biológicas y Biodiversidad, Universidad de Los Lagos, Osorno, Chile Piscícola Huililco Ltda., Pucón, Chile Departamento de Estadística, Universidad del Bío-Bío, Concepción, Chile

Sex hormone-binding globulin b expression in the rainbow trout ovary prior to sex differentiation

Salmonids have two sex hormone-binding globulin (Shbg) paralogs. Shbga is mainly expressed in the liver, while Shbgb is secreted by the granulosa cells of the rainbow trout ovary. Coexpression of shbgb and the gonadal aromatase cyp19a1a mRNAs been observed in granulosa cells, suggesting a physiological coordination between Shbgb expression and estrogen synthesis. As estrogens are essential for female sex determination in the fish ovary, we propose that Shbgb participates in early ovarian differentiation, either by binding with estrogen or through another mechanism that remains to be discovered. To elucidate this potential role, monosex populations of female trout were studied during the molecular ovarian differentiation period (28-56 dpf). shbgb mRNA expression was measured using qPCR and compared with expression of genes for other ovarian markers (cyp19a1a, foxl2, follistatin, and estrogen receptors). shbgb transcript expression was detected during the final stages of embryonic development (21-26 dpf) and during molecular ovarian differentiation (32-52 dpf) after hatching (which occurred at 31 dpf). In situ hybridization localized shbgb transcription to the undifferentiated ovary at 42 dpf, and shbgb and cyp19a1a mRNA showed similar expression patterns. These results suggest that Shbgb is involved in early ovarian differentiation, supporting an important role for the salmonid shbgb gene in sex determination.