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Background: Blue-colored phenotypes have the potential to enhance the external appearance of rainbow trout for marketing due to their attractive skin coloration. However, further analyses are necessary to assess their overall performance for fish farming purposes. Objective: To investigate a blue-colored strain of rainbow trout in order to determine whether growth performance and spotting variation of the skin, either in number or size, are related to Blue Color Intensity on the back skin (BCI). Method: A correlation analysis and comparisons among trout separated into Low- and High-BCI categories were carried out in three blue-colored groups of rainbow trout. Results: In all groups, BCI was significantly and positively related to body weight (0.01 < P < 0.05). There was a significant and negative association between BCI and the number of dark spots in one group (P < 0.001), whereas no significant association was observed among BCI and dark spot size in any of the groups (P > 0.05). In one group, a significantly higher body weight (P < 0.05) was observed in the High-BCI (BCI ≥ 50%) than in the Low-BCI (BCI < 50%) category. The same pattern was observed in two groups (P < 0.05) when the lowest (1st) and highest (4th) quartiles of BCI were compared. In one group, number of dark spots was significantly lower in the High-BCI (≥ 50% and 4th quartile) than in the Low-BCI (< 50% and 1st quartile) category (P < 0.01 and P < 0.05, respectively). Dark spot size presented no significant differences among BCI categories (P > 0.05) in any of the groups. Conclusion: Results suggest that trout with more intensely blue colored skin has better growth performance and relatively less spotted skin than less intensely blue-colored specimens. These characteristics may represent an interesting advantage for using this class of trout in intensive fish farming.

Background:Skin pigmentation in fish is involved in various biological processes. In salmonids, the interactions of skin spottiness with biometric and reproductive parameters are mostly unknown, especially in naturalized populations influenced by different ecological factors.Objective:To associate skin spottiness variation with biometric and reproductive parameters in broodstocks of naturalized rainbow trout populations from southern Chile.Method:The number of dark spots below the lateral line was assessed in male and female broodstocks of rainbow trout from two reproductive seasons, years 2007 and 2012, and then this dataset was associated with biometric and reproductive parameters of the same individuals, using multivariate data analysis in the form of stepwise forward multiple regression.Results:Male body weight from year 2007 had a significant negative influence on the number of dark spots below the lateral line (P< 0.01), while the reproductive variables egg diameter and spawning time of females from years 2007 and 2012, respectively, had a significant positive influence on this parameter (P< 0.01).Conclusion:Our results indicate that there are male biometric parameters with a significant negative influence on skin spottiness. Our data also reveal that some reproductive parameters have a positive influence on skin spottiness. The identification of these reproductive parameters related to spottiness variation would reflect the reproductive quality of female broodstocks living in natural environments.

Naturalized rainbow trout (Oncorhynchus mykiss) populations are an important recreational fishing resource in the Araucanian lakes of southern Chile, but few reproductive studies have been undertaken to assess their sustainability. It is important to address this issue, since this analysis may provide information for improving management activities. In this study we carried out a biometric and reproductive analysis of naturalized rainbow trout breeders to describe their performance and to explore the variables that could determine fecundity, fertilization in addition to egg survival and size. We collected naturalized rainbow trout breeders from six tributaries of Calafquen Lake, during 2006, 2007 and 2012 to record their biometric and reproductive traits. Spawning and incubation were performed under controlled conditions in a hatchery facility to improve the recording process. In each spawning season, total fecundity (TF, No. of eggs/female), relative fecundity (RF, No. of eggs/kg female), fertilization rate (FR, %), egg diameter (ED, mm) and eyed egg survival (EES, %) were modeled as a function of biometric and reproductive parameters, using general linear mixed models. We used this statistical tool to explore the relationships between these reproductive traits and other breeder traits in order to identify all the potential combinations that could be linked to TF, RF, FR, ED and EES. The spawning period ranged from September to November (i.e., spring spawning season), with a clear spawning peak in October in all reproductive seasons. Mean TF (from 2275.9 to 3438.7) and RF (from 1730.5 to 1909.8) fell within the range of, or were close to, data reported for other Araucanian lakes, respectively. Mean values of FR and EES were relatively high, ranging from 88.8% to 93.3% and between 83.4% and 88.8%, respectively. Models indicated that TF is significantly affected by the interaction between female body weight and egg weight, while RF is affected by the combination of female body length and egg weight. In addition, a positive correlation was observed between female body weight and total fecundity, while an inverse association was recorded between relative fecundity and female body length. This trend is in accordance with the trade-off pattern between egg number and fish size described for naturalized populations of rainbow trout from the Northern Hemisphere. However, regression equations output suggests that the reproductive performance of the Calafquen Lake population has a more depleted fecundity in comparison either with naturalized populations from the Northern Hemisphere, or with cultured stocks of this species. Models for ED revealed that this variable is affected by egg weight and also by body length or body weight, all with positive correlations. This result concurs with observations reported for other naturalized populations of rainbow trout from North America, further supporting evidence that larger females of this species produce larger eggs than smaller females. Models for EES revealed the significant positive effect of fertilization rate and relative fecundity, being the latter an unexpected result, given that insignificant correlations between these variables have been found in cultured stocks of this species. Overall, the population analyzed exhibited a regular spawning period, and an optimal reproductive performance in terms of egg survival. To promote the sustainability of the naturalized rainbow trout of Calafquen Lake, we recommend the use of hatchery propagation of wild adults to support the production of fry to be used in subsequent restocking activities. This management effort can benefit because the broodstocks have a short spawning period during their spring run.

The Pudu deer (Pudu puda) is endemic to the temperate rainforest of Chile and Argentina and currently faces serious conservation problems related to habitat loss. However, studies undertaken on this species are not sufficient to identify suitable areas for conservation purposes across its distribution range. In order to estimate the current and future distribution of the Pudu deer in southern Chile, we modelled the potential distribution of this species, based on occurrence points taken from seven contiguous provinces of this area using the Maxent modelling method. The Pudu deer distribution covered an estimated area of 17,912 km2 (24.1% of the area analysed), using a probability of occurrence above 0.529, according to the threshold that maximises the sum of sensitivity and specificity. In contrast to the Andes mountain range, areas with higher probabilities of occurrence were distributed mainly on the eastern and western slopes of the Coastal Mountain Range, where extensive coverage of native forest persists, as occurs in the provinces of Ranco, Osorno and Llanquihue. Projections to 2070, with global warming scenarios of 2.6 and 8.5 rcp, revealed that large areas will conserve their habitability, especially in the Coastal mountain range. Our results reveal that the Coastal mountain range has a high current and future habitability condition for the Pudu deer, a fact which may have conservation implications for this species.

Background: DNA-based technologies are reliable authentication methods for food products, enabling the detection of fraud, non-intentional substitution and control of mislabeling. The Chilean blue mussel (Mytilus chilensis) is a seafood commercialized in Chile under different formats, including packages of frozen specimens. In this format, the valves of mussels are removed during processing, thus impeding identification of the product by the consumer due to the lack of external characters. Objective: To assess the authenticity of frozen Chilean blue mussels commercialized in southern Chile, particularly in the town of Osorno. Methods: Six commercial brands of frozen Chilean blue mussel were authenticated by the Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) method, based on the analysis of an 18S rDNA fragment. Results: Restriction patterns obtained indicate that three brands (50%) proved to be 100% authentic, given that all specimens contained in the package were Chilean blue mussels. The other three brands (50%) contained specimens of other commercial mytilids, particularly the cholga mussel (Aulacomya ater), in a variable percentage (12.5-50%). Conclusion: This study based on the PCR-RFLP method provides evidence that Chilean blue mussels commercialized in a town located in southern Chile lack authenticity. This finding highlights the necessity for national producers to improve the production and/or packaging processes of this seafood. The authentication of commercial mussels is a matter of consumer interest and has been described in a recent patent on this issue that proposes an alternative methodology.

Samastacus spinifrons (Philippi, 1882), is the only South American parastacid that inhabits both rivers and lakes. The literature on this species reports certain morphological differences between representatives of lake and river populations. The aim of this study was to analyse the degree of differentiation of these morphological variations through multivariate analysis, and to explore the possible causes at a genetic level, by undertaking genetic divergence analysis using 18S and 28S ribosomal DNA molecular markers, and the mitochondrial cytochrome c oxidase subunit I (COI) gene. The material analysed was collected from five populations of central-southern Chile, two of which were lake and three were river populations. Our results show that marked morphological differences exist between lake morph and river morph individuals. These differences are related with the size of the rostrum, cephalothorax, chelae of the first pair of pereopods (P1) and phallic papillae. The lake specimens present a larger body size, a longer rostrum and more elongated, less thick P1 chelae and longer phallic papillae. Similarly, their body spinulation is significantly more prominent. Nevertheless, this level of morphological differentiation did not correlate positively with the genetic divergence analysis, since only scarce genetic differentiation was observed between representatives of the lake and river morphs of S. spinifrons. These results suggest that the morphs analysed would emerge as a consequence of the phenotypic plasticity phenomenon. Thus, this morphological variability could be explained by the adaptation of S. spinifrons specimens of a similar genetic constitution, to limnic environments with very different dynamics.

Although the rainbow trout Oncorhynchus mykiss (Walbaum, 1792) is considered a single-time spawner with a restricted annual reproduction cycle (Mylonas and Zohar, 2007), some female broodstocks of this species may display an unusual reproductive periodicity, resulting in a phenomenon characterized by two consecutive annual spawnings as a consequence of biannual spawning behavior (Hume, 1955; Aida et al., 1984; Gall and Crandell, 1992). In these broodstocks (called ‘twice-spawners’), the first and second spawning occurs during a normal reproductive cycle (NRC) and an additional reproductive cycle (ARC, respectively). Moreover, the spawning rate in the ARC is usually lower than in the NRC and is highly variable across strains and spawning seasons (Tazaki et al., 1993; Takano et al., 1995; Shrable and Orr, 1998). In addition, the gonadal maturation period previous to the second spawning event, i.e. in the ARC, is a short-term process in these broodstocks, in comparison with the single-time spawner in which gonadal maturation begins a year before ovulation (Elliott et al., 1984; Sumpter et al., 1984). Reproductive performance (Aida et al., 1984; Kincaid, 1985; Tazaki et al., 1993; Takano et al., 1995; Shrable and Orr, 1998), sex hormone profiles (Lou et al., 1984), and gonadosomatic index and gonadal histology (Estay et al., 2012) studies have found that no major reproductive disruptions occur in female twice-spawner rainbow trout. In addition, the examination of the spawning period dynamics indicates that this is longer in the ARC than in the NRC (Tazaki et al., 1993; Takano et al., 1995); furthermore, the inter cycle length (ICL), a parameter that expresses the time required until the occurrence of the additional spawning event for the same female, generally covers a period either from 126 to 180 days (Takano et al., 1995) or from 112 to 217 days (Tazaki et al., 1993). In spite of this progress, additional studies are needed to compare twice-spawner strains of different origin, to assess whether their particular spawning dynamics follow a general pattern. Therefore, in order to gain an insight into this issue, we examined twice-spawner female broodstocks from a fish hatchery in southern Chile to ascertain the pattern of the NRC, ARC and the ICL following the spawning behavior of individually-tagged breeders. Furthermore, to form a better view of the dynamics of this phenomenon, the relationships between NRC and ARC and between ICL and ARC were also assessed. This study presents the results of the spawning dynamics of biannual spawning behavior in rainbow trout, obtained by studying some characteristic reproductive parameters such as the NRC, ARC and the ICL, derived from the analysis of twice-spawner female broodstock from southern Chile.

Trichomycterus areolatus Valenciennes, 1846 is a small endemic catfish inhabiting the Andean river basins of Chile. In this study, the morphological variability of three T. areolatus populations, collected in two river basins from southern Chile, was assessed with multivariate analyses, including principal component analysis (PCA) and discriminant function analysis (DFA). It is hypothesized that populations must segregate morphologically from each other based on the river basin that they were sampled from, since each basin presents relatively particular hydrological characteristics. Significant morphological differences among the three populations were found with PCA (ANOSIM test, r = 0.552, p < 0.0001) and DFA (Wilks’s λ = 0.036, p < 0.01). PCA accounted for a total variation of 56.16% by the first two principal components. The first Principal Component (PC1) and PC2 explained 34.72 and 21.44% of the total variation, respectively. The scatter-plot of the first two discriminant functions (DF1 on DF2) also validated the existence of three different populations. In group classification using DFA, 93.3% of the specimens were correctly-classified into their original populations. Of the total of 22 transformed truss measurements, 17 exhibited highly significant (p < 0.01) differences among populations. The data support the existence of T. areolatus morphological variation across different rivers in southern Chile, likely reflecting the geographic isolation underlying population structure of the species.

The coloration (relative area covered by blue/sky-blue hue) and spottiness (number of dark spots, compactness of dark spots, regularity of dark spots, and the relative dorsal-to-lateral line position of the dark spots) of the dorsal skin were analyzed in nine stages (from 282 to 447 days post fertilization) in a group of juvenile Blue Back (BB) rainbow trout to characterize the origin of these attributes. A group of non-Blue Back (NBB) rainbow trout was used for comparison. These parameters were studied by computer-based image analysis. The percentage of blue/sky-blue hue on the skin of the BB group was significantly higher than the NBB group (P < 0.05). Only the BB group exhibited a constant value for blue/sky-blue hue through the nine stages analysed, in contrast with the NBB group, which experienced decreasing values at final stages. The mean number of spots, the compactness, and the relative dorsal-to-lateral line position of the dark skin markings were not significantly different between the BB and N...

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...

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.

Skin color is an important commercial trait in fish farming, given that this phenotype influences consumer acceptance, thereby determining the commercial value that fish can reach. This character is genetically determined, either by monogenetic or polygenetic control. Over the past few years, progress has been made in studies of quantitative genetic parameters for commercially important traits related to skin pigmentation and, in the molecular field, the mapping and cloning of some genes involved in fish color determination. This study reviews information regarding the genetic determination of salmonid skin color, along with different strategies to improve this character. Data collected in model fish (medaka and zebrafish) are also considered since this information contributes considerably towards improving understanding of the genes that may participate, and of the mechanisms involved in establishing skin coloration in salmonids.

In this paper new mitochondrial COI sequences of Common Barn Owl Tyto alba (Scopoli, 1769) and Short-eared Owl Asio flammeus (Pontoppidan, 1763) from southern Chile are reported and compared with sequences from other parts of the World. The intraspecific genetic divergence (mean p-distance) was 4.6 to 5.5% for the Common Barn Owl in comparison with specimens from northern Europe and Australasia and 3.1% for the Short-eared Owl with respect to samples from north America, northern Europe and northern Asia. Phylogenetic analyses revealed three distinctive groups for the Common Barn Owl: (i) South America (Chile and Argentina) plus Central and North America, (ii) northern Europe and (iii) Australasia, and two distinctive groups for the Short-eared Owl: (i) South America (Chile and Argentina) and (ii) north America plus northern Europe and northern Asia. The level of genetic divergence observed in both species exceeds the upper limit of intraspecific comparisons reported previously for Strigiformes. Therefore, this suggests that further research is needed to assess the taxonomic status, particularly for the Chilean populations that, to date, have been identified as belonging to these species through traditional taxonomy.

Data on reproductive traits in a cultured population of brown trout (Salmo trutta L.) in southern Chile were collected over three consecutive reproductive seasons: 1999, 2000 and 2001, corresponding to the first (at 3 years), second and third spawnings in females. Data were collected from individual females (n=238, 273 and 169 respectively). The reproductive season lasted mainly from June to August. The peak (July) tended to increase with each season (55.46%, 62.27% and 80.81% of total spawning fish respectively). Female body weight (470.8±102.5, 735.0±150 and 1263.9±263.4 g), total fecundity (1182±344, 1904±595 and 2744±605) and egg diameter (4.64±0.11, 4.67±0.27 and 5.24±0.12 mm) increased significantly (P

Naturalized brown trout populations in Chile are a valuable genetic resource with aquaculture potential. The oogenesis of a three-year-old brown trout cultured population was studied in southern Chile. Gonadosomatic index (GSI), oocyte growth, gonadal microscopic characteristics, and plasma levels of estradiol–17β (E2), testosterone (T), and 17α–hydroxyprogesterone (17α–HP) were measured bimonthly for a nine-month period before spawning. The maximum GSI level (22%) was similar to that described for other salmonids, although it was reached in May, more than one month before the population started spawning. Oocyte growth increases strongly from January when diameter reaches more than 1 mm. The vitellogenic period (six-seven months) is consistent with the long vitellogenesis, described for salmonid females maturing at three years old. E2 shows a slow increase from November, reaching its peak value in March (65.2±0.7 ng/ml), during maximal vitellogenic activity. T increases as oogenesis progresses, reaching a maximum of 90±20 ng/ml during May, and falling considerably during ovulation. Following a typical pattern of progestogens in salmonid oogenesis, 17α–HP stays at basal levels during most of oogenesis, but experiences a strong surge (2.0±0.4 ng/ml) just before ovulation. J. Exp. Zool. 298A:60–66, 2003. © 2003 Wiley-Liss, Inc.

Appearance traits in fish, those external body characteristics that influence consumer acceptance at point of sale, have come to the forefront of commercial fish farming, as culture profitability is closely linked to management of these traits. Appearance traits comprise mainly body shape and skin pigmentation. Analysis of the genetic basis of these traits in different fish reveals significant genetic variation within populations, indicating potential for their genetic improvement. Work into ascertaining the minor or major genes underlying appearance traits for commercial fish is emerging, with substantial progress in model fish in terms of identifying genes that control body shape and skin colors. In this review, we describe research progress to date, especially with regard to commercial fish, and discuss genomic findings in model fish in order to better address the genetic basis of the traits. Given that appearance traits are important in commercial fish, the genomic information related to this issue promises to accelerate the selection process in coming years.

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.

Six Artemia populations from coastal and inland sites in Chile, ranging from 20 to 50 degrees latitude south, were compared morphologically. The study included reference samples of A. franciscana (San Francisco Bay, California-USA) and A. persimilis (Buenos Aires, Argentina). These species are likely to be found in Chile. Samples from Peru (Piura) and Brazil (Macau, Rio Grande do Norte) are two known examples of deliberate introduction of A. franciscana. The hypothesis of A. franciscana being the dominant species in South America was tested by multivariate morphological analysis based on ten body measurements. In addition, laboratory cross-fertility tests were performed in order to evaluate levels of reproductive isolation among these widely distributed populations. The analysis showed that A. franciscana and A. persimilis are morphologically divergent. A number of populations overlap with the San Francisco Bay sample, two are morphologically close to Buenos Aires, whilst others lie morphologically in between. Interpopulation morphological differences along with geographical and, probably, ecological divergence do not reflect reproductive isolation, at least of the pre-mating type. The morphological similarity of two Chilean samples with A. persimilis suggests that the distribution of A. persimilis should be further investigated. A multi-trait approach for Artemia characterization is stressed as a way to obtain better descriptions and interpretations of the biological diversity in the genus.

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.

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.

Cytogenetic analysis of Trichomycterus areolatus, collected from the Tijeral and Huilma Rivers in southern Chile has shown a diploid chromosome number of 2n = 54, a fundamental number of FN = 106, and a karyotypic formula of 44m + 8sm + 2st. Intra-individual polymorphism of chromosome number (2n = 54, 55 and 56) in specimens from the Huilma River has also been documented, providing further evidence of the occurrence of this phenomenon in Trichomycterus. The karyotype exhibited large chromosome pairs: metacentric pairs 1 (relative length 7.54%), 2 (5.75%) and 3 (5.09%), submetacentric pair 23 (5.25%), and subtelocentic pair 27 (5.28%). Nuclear DNA content analysis showed an average value of 5.04 ± 1.09 pg/nucleus. This DNA content is higher than the mean value described for other species in this genus.

Naturalized brown trout populations in Chile are a valuable genetic resource with aquaculture potential. The oogenesis of a three-year-old brown trout cultured population was studied in southern Chile. Gonadosomatic index (GSI), oocyte growth, gonadal microscopic characteristics, and plasma levels of estradiol-17beta (E2), testosterone (T), and 17alpha-hydroxyprogesterone (17alpha-HP) were measured bimonthly for a nine-month period before spawning. The maximum GSI level (22%) was similar to that described for other salmonids, although it was reached in May, more than one month before the population started spawning. Oocyte growth increases strongly from January when diameter reaches more than 1 mm. The vitellogenic period (six-seven months) is consistent with the long vitellogenesis, described for salmonid females maturing at three years old. E2 shows a slow increase from November, reaching its peak value in March (65.2+/-0.7 ng/ml), during maximal vitellogenic activity. T increases as oogenesis progresses, reaching a maximum of 90+/-20 ng/ml during May, and falling considerably during ovulation. Following a typical pattern of progestogens in salmonid oogenesis, 17alpha-HP stays at basal levels during most of oogenesis, but experiences a strong surge (2.0+/-0.4 ng/ml) just before ovulation.

Chromosomal characterization of coho salmon samples from three fish farms in southern Chile (Polcura, Castro and Coyhaique) was carried out in order to compare their chromosome constitutions. All populations had a 2n = 60; however, Polcura and Coyhaique had a different chromosome arm number (NF = 110; 40m + 10sm + 10st/t) than Castro (NF = 108; 40m + 8sm + 12st/t). Variation in NF was due to chromosome pair 25, which was submetacentric in Coyhaique and Polcura, but subtelocentric in Castro. In all karyotypes, a large submetacentric chromosome pair exhibited an interstitial secondary constriction in the short arm. The observed variability in chromosome arm number agrees with previous reports for O. kisutch, and in this particular case it seemed to be caused by a pericentric inversion of pair 25. Cultured populations of Chilean coho salmon are, therefore, likely to be cytogenetically variable.A caracterização cromossômica de amostras de salmon tipo coho de três criações de peixes do sul do Chile (Polcura, Castro e Coyhaique) foi feita com a intenção de comparar suas constituições cromossômicas. Todas as populações apresentaram 2n = 60; contudo, Polcura e Coyhaique tiveram um número de braços cromossômicos (NF = 110; 40m + 10sm + 10st/t) diferente de Castro (NF = 108; 40m + 8sm + 12st/t). A variação no NF deveu-se ao par cromossômico 25, que era submetacêntrico em Coyhaique e Polcura e subtelocêntrico em Castro. Em todos os cariótipos, um grande par cromossômico submetacêntrico exibiu uma constrição secundária intersticial no braço curto. A variabilidade observada no número de braços cromossômicos concorda com relatos prévios para O. kisutch e, neste caso particular, parece ter sido causada por uma inversão pericêntrica no par 25. Portanto, populações cultivadas de salmão chileno do tipo coho provavelmente são citogeneticamente variáveis.