尼罗罗非鱼和萨罗罗非鱼遗传生殖隔离的初步证据(英文)

罗非鱼类(Tilapiini)含3个属70余种,种间和属间颇易人工杂交,但尼罗罗非鱼(Oreochromis niloticus)和萨罗罗非鱼(Sarotherodon melanotheron)人工杂交难度大,产苗概率甚低,要获得数量足够的可用于生产的杂交子代相当困难。该文对这两种鱼及其正交(O.niloticus♀×S.melanotheron♂)和反交(S.melanotheron♀×O.niloticus♂)子代的头肾细胞的核型进行了比较。此外,采用同工酶电泳方法检测肾、肝、眼、肌肉、心中乳酸脱氢酶等4种同工酶的表型差异。4种遗传型罗非鱼具有相同的染色体二倍数(2n=44)和总臂数(NF=50),但各具不同的染色体类型,尼罗罗非鱼为3对近中着丝点染色体(sm)、12对近端着丝点染色体(st)和7对端着丝点染色体(t);萨罗罗非鱼为1对中间着丝点染色体(m)、2对sm、12对st和7对t;正反杂交子代表现为介于双亲之间的混合类型,为0.5对m、2.5对sm、12对st和7对t。在同工酶中,仅见肾脏乳酸脱氢酶电泳结果有清晰差异,尼罗罗非鱼出现5条谱带,萨罗罗非鱼3条,而杂交子代6条,且所有谱带的迁移率和活性均表现出多态性。据此初步认为,核型和同工酶方面的差异可能是导致这两种不同属罗非鱼生殖隔离的遗传原因,这些差异也可能为这两种(属)鱼的分类学提供新的遗传背景资料。     

Protective effect of selenium against mercury-induced toxicity on hematological and biochemical parameters of Oreochromis niloticus

In this study, to identify mercury (Hg) toxicity and whether selenium (Se) has any role in alleviation of this toxicity, it was investigated the changes in hematological and serum biochemical parameters of Oreochromis niloticus. Fish were exposed to 0.01 and 0.1 mg/L Hg and 0.01 mg/L Hg + 0.1 mg/L Se and 0.1 mg/L Hg + 1.0 mg/L Se for 7 and 14 days. The exposure of O. niloticus to Hg alone resulted in decreases in red blood cell, white blood cell, hemoglobin, hematocrit values, and cholinesterase activity while it increased in alanine aminotransferase and aspartate aminotransferase activities and cortisol and glucose levels. Se, in combination with Hg, partially or totally caused an alleviation for the toxic effect of Hg on the above mentioned hematological and biochemical parameters. The results of our study showed that Se has a protective effect against toxicity induced by Hg.     

Identification of the Lake Malawi Oreochromis (Nyasalapia) spp. using multivariate morphometric techniques

With the aim of reliably distinguishing these commercially important species on the basis of external characteristics alone, morphometric techniques were employed on a sample of the four species of Oreochromis ( Nyasalapia ) described from Lake Malawi: O. karongae, O. lidole, O. saka and O. squamipinnis . Univariate analysis of variance on the ratios of 23 variables to standard length indicated many differences among all species, but there was considerable individual variation, and consequent overlap. Residuals from a regression of each variable on length were employed for multivariate analysis. Cluster analysis on the means of the residuals was used to construct a phenogram which formed the basis for denning a series of dichotomous discriminant analyses. In each discriminant analysis, variables were successively eliminated in the reverse order of the magnitude of their correlation with the discriminant function. The combination of variables producing 95% accuracy of classification was selected, and the discriminant function equations for each step calculated. Some further variables were eliminated by checking for redundancy through analysis of correlations. The resulting equations enable O. karongae to be separated using eight measurements, O. lidole using 10, and O. saka and O. squamipinnis to be distinguished by a combination of 13 measurements.     

Metazooplankton dynamics in the Salton Sea, California, 1997–1999

The dynamics of metazooplankton populations were studied over 3 years at the saline (43 g l^–1) Salton Sea, California's largest lake. Total abundance was highest in summer following late winter/early spring phytoplankton blooms. At this time, metazooplankton consisted mostly of the copepod, Apocyclops dengizicus, and the rotifer, Brachionus rotundiformis. In August or September, severe crashes in the metazooplankton populations occurred each year in mid-lake due to strong wind events which increased mixing and caused low oxygen and high sulfide concentrations throughout the water column. Larvae of the polychaete worm, Neanthes succinea and the barnacle, Balanus amphitrite were present mostly in late winter and spring. Their scarcity in summer is due in part to persistent anoxic bottom conditions that decrease adult populations and in part to predation by tilapia, an omnivorous fish that has become abundant in the lake since the 1960s. Two Synchaeta species, rotifers not previously reported from the Sea, were abundant in winter and spring and predation on these may have permitted the copepod to persist at low levels through the winter. There were two major changes in metazooplankton dynamics since 1954–1956 in addition to the appearance of the two synchaetid rotifers in the fauna. First, there are now much lower densities of barnacle and polychaete larvae in the fall, probably due to the invasion of the zooplanktivorous fish, tilapia. Second the precipitous crashes now seen in metazooplankton densities, especially the copepod, in late summer-early fall did not occur in the 1950s possibly because fall overturn events did not result in such high sulfide levels.     

Treatment with an aromatase inhibitor suppresses high-temperature feminization of genetic male (YY) Nile tilapia

High temperature (36° C) treatment during sexual differentiation caused significant changes in sex ratio in YY male Nile tilapia Oreochromis niloticus fry (64.5% males compared to 100.0% males at 28° C), while dietary treatment with a chemical aromatase inhibitor (AI: Fadrozole™ CGS16949A) during this period suppressed the high temperature feminization (98.9% males). This implies that cytochrome P450 aromatase is mechanistically associated with temperature-dependent sex determination (TSD) in this species. XY male fry did not show significant sex reversal at 36° C. In XX female fry, high temperature treatment resulted in significant masculinization (62.5% males compared with 21.9% males at 28° C), while treatment with AI at either temperature resulted in very high proportions of males (100.0% males at 36° C; 99.0% males at 28° C). These results confirm the importance of aromatase in sexual differentiation in the Nile tilapia below the TSD threshold and suggest that it also plays a role in TSD, at least in the YY genotype.     

Isolation and Physical Mapping of Sex-Linked AFLP Markers in Nile Tilapia (Oreochromis niloticus L.)

Gynogenetically produced XX and YY Nile tilapia (Oreochromis niloticus) and diploid control groups were screened for amplified fragment length polymorphisms (AFLPs) to search for sex-linked or sex-specific markers. Family-level bulked segregant analysis (XX and YY gynogenetic family pools) and individual screening (XX and YY gynogenetics and XX and XY control individuals) identified 3 Y-linked (OniY425, OniY382, OniY227) and one X-linked (OniX420) AFLP markers. OniX420 and OniY425 were shown to be allelic. Single locus polymerase chain reaction assays were developed for these markers. Tight linkage was demonstrated between the AFLP markers and the sex locus within the source families. However, these markers failed to consistently identify sex in unrelated individuals, indicating recombination between the markers and the sex-determining loci. O. niloticus bacterial artificial chromosome clones, containing the AFLP markers, hybridized to the long arm of chromosome 1. This confirmed previous evidence, based on meiotic chromosome pairing and fluorescence in situ hybridization probes obtained through chromosome microdissection, that chromosome pair 1 is the sex chromosomes.     

Identification of putative sex chromosomes in the blue tilapia, Oreochromis aureus, through synaptonemal complex and FISH analysis

Sex determination in the blue tilapia, Oreochromis aureus, is primarily a ZW female-ZZ male system. Here, by analysis of the pachytene meiotic chromosomes of O. aureus, we demonstrate the presence of two distinct regions of restricted pairing present only in heterogametic fish. The first, a subterminal region of the largest bivalent is located near to the region of unpairing found in the closely related species O. niloticus, while the second is in a small bivalent, most of which was unpaired. These results suggest that O. aureus has two separate pairs of sex chromosomes.