Nelson F. Díaz

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.

Genetic differences among year classes in a hatchery population of coho salmon (Oncorhynchus kisutch (Walbaum, 1792)) in Chile

Abstract Coho salmon (Oncorhynchus kisutch (Walbaum, 1792)) was first introduced into Chile from the USA in 1930 and has become an important species for aquaculture. The current Chilean coho salmon aquaculture industry is largely based on eggs imported from the Pacific Northwest. In order to reduce dependence on North America for seed and to improve genetically coho salmon stock in Chile, the Instituto de Fomento Pesquero and the University of Chile started a breeding program at the Coyhaique Hatchery, Region XI of Chile. The genetic variability in two groups of broodstock was determined by horizontal starch gel electrophoresis of allozymes. Twenty-six enzyme systems, representing 51 loci, were resolved. Seven loci were variable (P=13.7%) and a mean heterozygosity (Hi) of 0.007 was estimated. Results indicated a reduction in polymorphism, but not in heterozygosity, with respect to information in the literature on other stocks of coho salmon. The most likely explanation for the results is the occurrence of founder effects while establishing the base population in the hatchery.

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...

Comparative studies on glucose phosphorylating isoenzymes of vertebrates: Identification and characterization of amphibian liver hexokinases☆

Abstract Glucose phosphorylating activities were measured in liver extracts from two urodeles and twenty-six anurans. Fractionation on diethylaminoethyl-cellulose columns of liver extracts from these amphibians permitted the recognition of four hexokinases which are called A, B, C, and D. However, any given amphibian displays only three liver hexokinases and the profiles so far observed are either of the type A-B-D or C-B-D. The distribution of the amphibians in either type of pattern does not show any simple taxonomic relationship. A wide generic and specific, but not individual, variation of the relative proportion of each isoenzyme was observed. Hexokinases A and B were shown to be low Km glucose isoenzymes (0.06 and 0.15 m m glucose, respectively) with normal hyperbolic kinetics. Hexokinase C, also a low Km isoenzyme (0.05 m m ) was found to be inhibited by excess substrate at physiological levels of glucose. Hexokinases A, B, and C were able to phosphorylate fructose, mannose, and 2-deoxyglucose at equal or higher rates than glucose when assayed at saturating sugar levels. Hexokinase D was found to be a high Km isoenzyme ( K 0.5 ⋍ 2 mM ) with sigmoidal saturation curves for glucose (Hill coefficient ⋍ 1.6). Fructose and mannose were also phosphorylated by this isoenzyme at about 70% of the glucose rate when studied at saturating sugar concentrations. The properties of the amphibian hexokinases are thus similar, although not identical, to those of mammalian hexokinases.

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...

Effect of 17α-methyltestosterone on growth and nitrogen excretion in masu salmon (Oncorhynchus masou Brevoort)

Abstract Growth and nitrogen excretion studies are important for understanding the mechanism of action of anabolic steroids on fish metabolism. Juveniles (0.7 g) of Oncorhynchus masou , a salmonid fish found in the northeastern Pacific, were fed daily for 84 days, diets supplemented with 0.1, 1.0, 3.0 and 7.0 mg/kg of 17 α -methyltestosterone (MT) to determine the effects on growth and nitrogen excretion. Feed conversion (FC), protein efficiency ratio (PER), nitrogen retention, and changes in moisture, protein and lipid in the carcass were also followed. On day 84, the increases in weight over the control were 20.4, 21.9 and 32.6% for salmon ingesting diets with 1, 3 and 7 mg/kg of MT, respectively. For the same hormonal dosages, FC showed declines of 19.9, 18.9 and 18.5% while values for PER and nitrogen retention were increased by 23.9, 27.2, 26.1% and 5.9, 5.4, 13.5%, respectively. For the hormonal dosages of 1, 3 and 7 mg/kg, ammonia excretion decreased by 19.3, 18.9 and 33.9% over control figures while urea excretion and body composition did not show meaningful changes with respect to MT dosage. Our findings suggest that MT partly exerts its anabolic action through growth increases and a decline in protein catabolism.

Larval morphology and phenetic relationships of the chilean Alsodes, Telmatobius, Caudiverbera and Insuetophrynus (Anura: Leptodactylidae)

The morphology and habitat preferences of eleven species of four genera of Chilean leptodactylid frogs were compared. Characters of these four genera allow a clear-cut separation and are elaborated in a key to their species. The larvae of Alsodes and Telmatobius show the highest degree of morphological and ecological similarity. Similarities and differences found between the larvae of both genera match in some cases the specific and generic relationships derived from adult morphology; the characters of the larvae of Telmatobius montanus suggest a closer relationship to Alsodes than to Telmatobius and we confirm the proposed change of genus for this species. The larvae of the monotypic genera Caudiverbera and Insuetophrynus are the most divergent, indicating strong specialization. Based on the characters obtained for the larvae of these four genera and adding those of Eupsophus, Batrachyla, Hylorina and Temaltobufo, we propose some generic relationships among these telmatobiine leptodactylid frogs.

Microhabitat utilization by two leptodactylid frogs in the Andes of central Chile

SummarySome basic parameters of the life history of Alsodes montanus and Alsodes tumultuosus (Anura-Leptodactylidae), were studied from 1977 to 1980 by periodic field observations at Farellones and La Parva (33–34° south lat.; 2,700–3,000 m above sea level). Special attention was paid to strategies of resource partitioning in relation to gross features of the environment. The latter was unstable with a relative short period favorable for activity of the animals. Physical environmental differences between the first and second season of this study, resulted in a decrease in total number of active adults, a reduction in the duration of larval activity and a shift in microhabitat preferences of larvae.During the favorable season, October to May, adults of both species showed spatial and temporal segregation, related to different physical features of the environment; larvae did not show temporal segregation. Larvae of both species were found in seven different microhabitats; only in one of these did they show significant difference in microhabitat preference, A. tumultuosus was found more often in crevices. Microhabitat dimensions were more important than time and food resources in the separation of the niches of the two species. The segregation of niche dimensions, microhabitat, diel and annual activity and food were not complementary.Coexistence was therefore observed with the species tending to use different resources. When the same resource was used, it was not limiting.