Metallothionein induction in early larval stages of tilapia (Oreochromis mossambicus)

Amounts of whole-body metallothionein (MT) in tilapia (Oreochromis mossambicus) larvae increased to a peak (1,500 ng mg(-1) protein) 1 d after hatching (H1), decreased rapidly thereafter, and was maintained at a constant level (700 ng mg(-1)) 3 d after hatching (H3). Waterborne Cd(2+) could stimulate MT expression in newly hatched (H0) larvae in dose-dependent and time-dependent patterns. H0 larvae, which were treated with 35 microg L(-1) Cd(2+) for 24 h, showed a 1.7-fold increase in the MT amount (174.0+/-64.7) and a 6. 5-fold increase in accumulated Cd(2+) but no significant change in Ca(2+) content, compared with the H0 control (MT, 102.6+/-48.1). H3 larvae with the same treatment revealed about a 10-fold increase in accumulated Cd(2+), a 10% decrease in Ca(2+) content, but no change in MT (261.2+/-120.0), compared with the H3 control (MT, 330+/-74.0). H0 larvae could synthesize more MT to bind Cd(2+) for detoxification in 35 microg L(-1) Cd(2+), a dose that would not affect normal physiology or survival of H0 larvae. On the other hand, 35 microg L(-1) Cd(2+) caused H3 larvae to experience hypocalcemia, an abnormal physiological condition, in which H3 larvae could not synthesize sufficient MT, thus causing greater than 25% mortality. These results indicate for the first time that the inducibility of MT by waterborne Cd(2+) is development dependent, being correlated with inconsistent sensitivities to Cd(2+) during larval development.     

Maternally derived Cu tolerance in larval fathead minnows: how long does it persist?

Fathead minnow Pimephales promelas larvae were produced by either copper (Cu)-exposed or naïve females and then subjected to a 96 h survival test using Cu concentrations of 400 and 800 μg l⁻¹. Three survival challenges were conducted: the first survival test featured 0 day-old larvae while the second and third featured 8 and 15 day-old larvae, respectively. The results of this study show that maternally derived Cu tolerance was relatively short-lived as it persisted for <8 days.     

Changes in gill epithelia of Oreochromis mossambicus subjected to cold shock

Synopsis Oreochromis mossambicus, 92–170 mm total length, were acclimated to 25° C and rapidly subjected to cold stress (20, 15, 10 and 5°C). Morphological changes in gill epithelia and ultrastructure were examined using light, scanning and transmission electron microscopy. Cold-stressed gills were unaffected morphologically at 20, 15, 10 and 5°C except for slight shrinkage; there was no evidence of cellular damage. This differs sharply with pronounced structural changes in gill morphology as reported previously for this species exposed to heat stress. Incapacitation of the neural system, inhibition of enzyme activity and osmoregulatory collapse are likely causes of death in cold-stressed O. mossambicus, a mode of death which contrasts with fishes exposed to heat shock.     

Changes in gill morphology of Oreochromis mossambicus subjected to heat stress

Synopsis The cichlid fish, Oreochromis mossambicus, was acclimated to 25°C for a 14 day period and then subjected to elevated temperatures of 30, 35, 40 and 45° C. Gill epithelia was progressively damaged from 30–40° C; gills from fish tested at 45°C showed less damage than those tested at 40°C. This is presumably due to the shorter exposure (survival) time at 45°C. Shrinkage of the secondary lamellae and the collapse of pillar cells supports the hypothesis that hypoxia at elevated temperatures is partially a function of changes in gill morphology.     

Maternal information and localized maternal mRNAs in eggs and early embryos of the ascidian Halocynthia roretzi

Summary

The mosaic behavior of blastomeres isolated from ascidian embryos has been taken as evidence that localized ooplasmic factors (cytoplasmic determinants) specify tissue precursor cells during embryogenesis. Experiments involving the transfer of egg cytoplasm have revealed the presence and localization of various kinds of cytoplasmic determinants in eggs of Halocynthia roretzi. Three cell fates, epidermis, muscle and endoderm, are fixed by cytoplasmic determinants. The three kinds of tissue determinants move in different directions during ooplasmic segregation. Prior to the onset of the first cleavage the three kinds of determinants reside in egg regions that correspond to the future fate map of the embryo and then they are differentially partitioned into specific blastomeres. In addition to tissue-specific determinants, there is evidence suggesting that ascidian eggs contain localized cytoplasmic factors that are responsible for controlling the cleavage pattern and morphogenetic movements. Transplantation of posterior-vegetal egg cytoplasm to an anterior-vegetal position causes a reversal of the anterior-posterior polarity of the cleavage pattern. Localized cytoplasmic factors in the posterior-vegetal region are involved in the generation of a unique cleavage pattern. When vegetal pole cytoplasm is transplanted to the animal pole or equatorial position of the egg, ectopic gastrulation occurs at the site of transplantation. This finding supports the idea that vegetal pole cytoplasm specifies the site of gastrulation. Recently, we started a cDNA project to analyze maternal mRNAs. An arrayed cDNA library of fertilized eggs of H. roretzi was constructed, and more than 2000 clones have been partially sequenced so far. To estimate the proportion of the maternal mRNAs that are localized in the egg and embryo, 150 randomly selected clones were examined by in situ hybridization. We found eight mRNAs that are localized in the eight-cell embryo, of which three were localized to the myoplasm (a specific region of the egg cytoplasm that is partitioned into muscle-lineage blastomeres) of the egg, and then to the postplasm of cleavage-stage embryos. These results indicate that the proportion of localized messages is much higher than we expected. These localized maternal messages may be involved in the regulation of various developmental processes.     

Maternal diet and larval diet influence survival skills of larval red drum Sciaenops ocellatus

Larval red drum Sciaenops ocellatus survival, turning rate, routine swimming speed, escape response latency and escape response distance were significantly correlated with essential fatty‐acid (EFA) concentrations in eggs. Of the five traits that varied with egg EFA content, two (escape response latency and routine swimming speed) were significantly different when larvae were fed enriched diets compared with the low fatty‐acid diet, indicating that the larval diet can compensate for some imbalances in egg composition. Turning rate during routine swimming and escape response distance, however, did not change when larvae predicted to have low performance (based on egg composition) were fed an enriched diet, indicating that these effects of egg composition may be irreversible. Escape response distances and survival rates of larvae predicted to perform well (based on egg composition) and fed highly enriched diets were lower than expected, suggesting that high levels of EFA intake can be detrimental. Altogether, these results suggest that both maternal diet, which is responsible for egg EFA composition, and larval diet may play a role in larval survivorship and recruitment.     

Maternal effects on early-life gut microbiota maturation in a wild nonhuman primate

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Temperature sensitivity of skeletal ontogeny in Oreochromis mossambicus

Sensitivity of skeletal ontogenesis to temperature was assessed in Mozambican tilapia Oreochromis mossambicus and culture temperature manipulations (22, 27 and 32° C) were used to establish if age or length gave the most suitable metric for standardization. Oreochromis mossambicus larval growth was composed of two growth stanzas: an initial period of rapid growth, followed by a slower growth phase. Irrespective of culture temperature chondrogenesis occurred during the first rapid growth phase and ossification was initiated during the second slower growth phase. The sequence of events and rate at which ossification occurred was much more sensitive to temperature than chondrogenesis. Cumulative counts provide a useful developmental index for skeletal ontogenesis; overall, age (effective days‐degrees) gave the best estimation of developmental status during chondrogenesis and the initiation of ossification, although standard length (as log₁₀ L _S) was a better metric for completion of ossification. The timing of development of functionally important structures, such as Meckel's cartilage, the branchial arches, the centra and the cleithrum important for breathing, feeding and swimming, was well conserved at all temperatures and may be a good index of teleost developmental stages.     

Host hybridization as a potential mechanism of lateral symbiont transfer in deep‐sea vesicomyid clams

Deep‐sea vesicomyid clams live in mutualistic symbiosis with chemosynthetic bacteria that are inherited through the maternal germ line. On evolutionary timescales, strictly vertical transmission should lead to cospeciation of host mitochondrial and symbiont lineages; nonetheless, examples of incongruent phylogenies have been reported, suggesting that symbionts are occasionally horizontally transmitted between host species. The current paradigm for vesicomyid clams holds that direct transfers cause host shifts or mixtures of symbionts. An alternative hypothesis suggests that hybridization between host species might explain symbiont transfers. Two clam species, Archivesica gigas and Phreagena soyoae, frequently co‐occur at deep‐sea hydrocarbon seeps in the eastern Pacific Ocean. Although the two species typically host gammaproteobacterial symbiont lineages marked by divergent 16S rRNA phylotypes, we identified a number of clams with the A. gigas mitotype that hosted symbionts with the P. soyoae phylotype. Demographic inference models based on genome‐wide SNP data and three Sanger sequenced gene markers provided evidence that A. gigas and P. soyoae hybridized in the past, supporting the hypothesis that hybridization might be a viable mechanism of interspecific symbiont transfer. These findings provide new perspectives on the evolution of vertically transmitted symbionts and their hosts in deep‐sea chemosynthetic environments.     

Immunocytochemical identification of prolactin cells in the pituitary gland of tilapia larvae (Oreochromis mossambicus: Teleostei)

Summary Using an antiserum to highly purified chum salmon prolactin, prolactin cells were identified in the putative rostral pars distalis of newly hatched tilapia larvae (Oreochromis mossambicus) by the immunogold method for the electron microscope. In the putative rostral pars distalis, some cells had another kind of secretory granule which was much less numerous, much smaller in size, and without immunoreactivity to salmon prolactin antiserum. Controls incubated with salmon prolactin-preabsorbed antiserum or normal serum showed no immunoreactive cells, confirming the specificity of the antiserum. The possible role of prolactin in the osmoregulation of tilapia larvae is discussed.     

长春花金属硫蛋白基因原核表达载体的构建及表达研究

将从长春花中克隆的金属硫蛋白基因（GenBank登录号：DQ016341）构建到高效原核表达载体pGEX-6P-1,并命名为pGEX-6P-1-CrMT,并对GST-CrMT融合蛋白的表达进行诱导和条件优化。对不同的诱导温度、IPTG诱导浓度和诱导时间等条件的优化结果表明,随诱导时间增长GST-CrMT融合蛋白表达量提高,22℃,24 h和37℃,240 min均能诱导GST-CrMT融合蛋白的最大量表达,在0.8 mmol·L^-1 IPTG浓度下可以有效诱导GST-CrMT融合蛋白的表达。     

Sexual dimorphism and allometry of external morphology in Oreochromis mossambicus

Sexual dimorphism in growth of conventional morphometric characters was investigated in juveniles and young adults (size range: 31 to 91 mm) of Oreochromis mossambicus . A closely associated set of traits was identified that shows sexually dimorphic growth, which was positively allometric in the males. These traits correspond to two different morphological complexes: jaw structure and anal/dorsal fins. The best sex discriminators among this set of traits were premaxilla width, anal fin height and snout length. These findings may be explained in terms of intra– and inter–sexual selection acting together and favouring males with strong and large mouths and high dorsal and anal fins, traits that are important in agonistic displays (jaw and fins), fighting and nest digging (jaw).     

Maternal influence on the incidence and duration of larval diapause in Calliphora vicina

ABSTRACT. The photoperiodic mechanism governing larval diapause in the blowfly Calliphora vicina R.-D. (Diptera: Calliphoridac) is largely maternal. The critical daylength for adult flies at 20C, and larvae derived from day 12 eggs and maintained in darkness at 11C, is about 14.5 h/24. At short daylength (LD 12:12 h) and a range of temperatures, eggs laid on or before day 9 gave rise to a low incidence of diapause, whereas those laid on day 10 and later gave rise to a high incidence; the photoperiodic 'counter' therefore shows a temperature-compensated mechanism for 'accumulating' successive short days. The rate of switching from non-diapause to diapause progeny is hardly affected by the timing of protein meals, although an early supply of meat accelerates egg development and leads to an increasing proportion of early, non-diapausing progeny. There is no evidence for a maternal effect preventing diapause induction in the first post-diapause ('spring') generation of flies. Diapausing larvae terminate diapause spontaneously in darkness at 11C after a variable period which is positively correlated with the incidence of diapause in the group. Diapause incidence and duration therefore are both determined maternally.     

Mitochondrion-rich cells in the embryonic yolk sac of Oreochromis mossambicus

By removing a small amount of yolk, tilapia embryos were dechorionated successfully as early as 30 h after fertilization. Using DASPEI, a mitochondrion-specific fluorescent stain, we were able to determine the first appearance of the mitochondrion rich cells on the surface of the yolk sac 26 h after fertilization ( c. 2 h after the beginning of gastrula stage). However, with scanning electron microscopy examination, no apical crypt could be found until 48 h after fertilization.     

Morphological changes of integumental chloride cells to ambient cadmium during the early development of the teleost, Oreochromis mossambicus

Synopsis Newly-hatched embryos of Oreochromis mossambicus were reared in freshwater and treated with 0 (control), 50 (low level) or 200 (high level) ppb cadmium for 4 days. Changes in the numbers and dimensions of chloride cell apical crypts on the skin of the free embryos were examined daily using scanning electron microscopy. The apical crypts of the chloride cells were rarely observed on the skin of the embryo trunk, and unevenly distributed on the surface of the yolksac. Two days after hatching, the chloride cells of the free embryos exposed to 50 ppb Cd were more active than those of the other two groups. Compared with the control group, the maximum dimensions of the developing apical crypts were stimulated by 50 ppb Cd and inhibited by 200 ppb Cd. The results indicated that the development of chloride cells in tilapia free embryos was provoked by low level Cd exposure and stunted by high level Cd exposure, suggesting the existence of structure/function relationships in which the activation of chloride cells may be related to the ionoregulatory mechanism in adaptation to Cd exposure.