Temperature-induced changes of survival, development and yolk partitioning in Chondrostoma nasus

Fertilized Chondrostoma nasus eggs were incubated at 10, 13, 16 and 19° C until full resorption of the yolk sac. High survival was observed at 10–16° C (89–92% at the onset of external feeding), whereas at 19) C survival was depressed (76%). The time at which 5, 50 and 95% of individuals had hatched, filled the swim bladder, ingested the first food and fully resorbed the yolk sac was determined. An increase in temperature accelerated development and made it more synchronous. Within the period from fertilization to hatching embryonic development was theoretically arrested (t_{0 dev}) at 8·8° C, and growth was arrested (t_0gr) at 8·86° C. For the whole endogenous feeding period (from fertilization to full yolk resorption) the amount of matter transformed into tissue was temperature independent between 10° and 19° C. Respiration increased exponentially with age; the respiration increase was faster at higher temperatures, but, in general, metabolic expenditures of C. nasus were low. As a consequence, the efficiency of utilizing yolk energy for growth was high as compared with other fish species (57% during the whole endogenous feeding period); it was temperature independent. However, time was used less efficiently at low temperatures, increasing a risk of predation. Within the endogenous feeding period a shift from lower to higher temperatures for optimal yolk utilization efficiency was observed. The temperatures optimal for survival and energetic performance seem to be 13–16° C for egg incubation and 15–18° C for rearing of yolk-feeding larvae. Chondrostoma nasus is a potential candidate for aquaculture for restocking purposes.     

A preliminary report on the development, growth and survival of laboratory reared larvae of the grey mullet, Mugil cephalus L.

Larvae from artificially bred grey mullet were reared in the laboratory and survival rates of 0.2 %, 5 % and 5 % achieved in three of six trials. Food consisted of wild zooplankton and Anemia nauplii. Feeding began on the fifth day, when the yolk sac was depleted, and intensified on the ninth day. The rate of yolk absorption and feeding intensity were reflected in the growth curve. Larval survival was not affected by withholding food from the larvae till the seventh day from hatching. Two critical periods associated with high larval mortality were apparent on the 2nd–3rd and 8th–11th days after hatching. These were preceded by an increase in specific gravity of larvae followed by passive sinking to the bottom of the rearing tank. Larval length increased from 2.63 mm at hatching to 17.69 mm at the end of the 42-day larval period. The larvae survived on benthic diatoms therefter. Maximum survival rates were achieved at 22°C. (Oceanic Institute Contribution No. 101).     

Cloning of a quail homologue of hatching enzyme: its conserved function and additional function in egg envelope digestion

The aim of the present study was to reveal molecular entities participating in the digestion of the egg envelope in the Japanese quail, Coturnix japonica. We isolated a 1,510-bp cDNA from extraembryonic tissues of developing embryos and designated it quail hatching enzyme (QHE) cDNA. The QHE cDNA was found to code a protein molecule comprising an astacin protease domain in the N-terminal half and a complement subcomponents C1r/C1s, Uegf, Bmp1 (CUB) domain in the C-terminal half. A phylogenetic analysis showed that QHE belonged to the hatching enzyme group and was distinct from other proteases in the astacin family. Northern blotting and in situ hybridization demonstrated that expression of the QHE mRNA occurred twice during the development: first in ectodermal cells of the yolk sac on days 0–5, then in those of the albumen sac on days 8–13. Zymography revealed that proteolytic activity in extracts of days 3–4 and 9–12 embryos appeared at the position of 40 kDa. Immunoblotting tests showed that anti-QHE antiserum stained a 40-kDa molecule in extracts of day 3 area vitellina. Anti-QHE antibody stained the ectodermal cells of the area opaca on days 0–1, those of the area vitellina of the yolk sac on days 2–5, and those of the albumen sac on days 9–12. The temporal and spatial expression pattern of QHE mRNA was closely associated with digestion of the vitelline membrane occurring on days 1–4, and with that of the egg white on days 9–12.     

Effect of incubation temperature on green sturgeon embryos, <Emphasis Type="Italic">Acipenser medirostris</Emphasis>

Regulation of river flow and the amount of winter rainfall are the major factors affecting the water temperature of the spawning grounds, for green sturgeon in the Klamath River. During the primary spawning period of green sturgeon, mid-April to June, the water temperature may vary from 8 to 21°C. To estimate the potential implications of this modified thermal regime, we examined the survival and development in three progeny groups of green sturgeon embryos from zygote to hatch, at constant incubation temperatures (11–26°C). Temperatures 23–26°C affected cleavage and gastrulation and all died before hatch. Temperatures 17.5–22°C were suboptimal as an increasing number of embryos developed abnormally and hatching success decreased at 20.5–22°C, although the tolerance to these temperatures varied between progenies. The lower temperature limit was not evident from this study, although hatching rate decreased at 11°C and hatched embryos were shorter, compared to 14°C. The mean total length of hatched embryos decreased with increasing temperature, although their wet and dry weight remained relatively constant. We concluded that temperatures 17–18°C may be the upper limit of the thermal optima for green sturgeon embryos, and that the river thermal regime during dry years may affect green sturgeon reproduction.     

Effects of incubation temperature on growth and development of embryos ofAlligator mississippiensis

Summary Eggs ofAlligator mississippiensis were incubated at 30 °C and 33 °C throughout incubation up to hatching. Every four days several eggs were opened and the albumen, yolk and extra-embryonic fluids removed and weighed. The embryo was removed and fixed prior to being staged, weighted and measured for various morphometric criteria. Development at 33 °C was accelerated compared with 30 °C in terms of yolk and albumen utilization and embryo growth. Significant losses in yolk mass did not occur until stage 22 at 33 °C but occurred at stage 18 at 30 °C. Different patterns in growth were observed in embryos at the two temperatures at similar morphological stages: between stages 18 and 22 embryos at 33 °C were smaller (in mass and length) compared with embryos at 30 °C despite being morphologically similar. The differences in growth and physiology between embryos at 30 °C (females) and 33 °C (males) were dependent on incubation temperature but not sex. Incubation at 33 °C accelerated both growth and development inAlligator; initially morphogenesis was accelerated by the higher temperature but later, growth rate was accelerated.     

Developmental rates of heterozygous and homozygous rainbow trout reared at three temperatures

The hatching distributions of rainbow trout (Salmo gairdneri) with different genotypes at eight loci are compared in two experiments with the same strain. Embryos were incubated at temperatures colder (5 and 8°C) and warmer (12°C) than normally experienced by these fish (9.5°C). At hatching, embryos were separated into five hatching groups representing the chronological order of hatching. There is no significant correlation between multilocus heterozygosity and hatching time at any temperature in either experiment. Fish in the middle of the hatching distribution had the highest average heterozygosity. In both experiments, heterozygotes at the majority of loci examined tended to hatch relatively later within the hatching distribution at 12°C than at both 5 and 8°C. Fish with different genotypes atPgm2 andCk1 showed significant differences in hatching time that were consistent between experiments.Ck1 heterozygotes hatched sooner than homozygotes at 8°C but later at 12°C.Pgm2 heterozygotes hatched later than homozygotes at all temperatures and significantly later in four of five cases. At the other loci examined, however, the relative hatching distributions of fish with particular genotypes were not significantly different or repeatable between experiments.This research was supported by National Science Foundation Grant BSR-8300039 awarded to Dr. Fred W. Allendorf. Moira M. Ferguson was supported by a postgraduate scholarship from the Natural Sciences and Engineering Research Council of Canada.     

Mouse Embryonic Development in a Serum-free Whole Embryo Culture System

Mid-gestation stage mouse embryos were cultured utilizing a serum-free culture medium prepared from commercially available stem cell media supplements in an oxygenated rolling bottle culture system. Mouse embryos at E10.5 were carefully isolated from the uterus with intact yolk sac and in a process involving precise surgical maneuver the embryos were gently exteriorized from the yolk sac while maintaining the vascular continuity of the embryo with the yolk sac. Compared to embryos prepared with intact yolk sac or with the yolk sac removed, these embryos exhibited superior survival rate and developmental progression when cultured under similar conditions. We show that these mouse embryos, when cultured in a defined medium in an atmosphere of 95% O₂ / 5% CO₂ in a rolling bottle culture apparatus at 37 °​C for 16-40 hr, exhibit morphological growth and development comparable to the embryos developing in utero. We believe this method will be useful for investigators needing to utilize whole embryo culture to study signaling interactions important in embryonic organogenesis.     

Temperature stress induces notochord abnormalities and heat shock proteins expression in larval green sturgeon (Acipenser medirostris Ayres 1854)

The effects of thermal stress on survival, development and heat shock protein (hsp) expression of green sturgeon (GS) yolk‐sac larvae, from hatching through yolk depletion were investigated to provide insight into effects of highly altered natural river hydrographs. Hatched GS larvae were reared at constant water temperatures 18°C (control) through 28°C at 2°C increments. Larval survival significantly decreased at 26–28°C, with 28°C being lethal. Significant proportions of deformed larvae were found at sub‐lethal (20–26°C) and lethal 28°C rearing temperatures, with kyphosis (i.e. backward flexion of notochord) accounting for >99% of morphological deformities. Histological analysis of larvae preparations indicate that elevated water temperature affects notochord cell function and physiology. At rearing temperatures 20–28°C, thermal stress elicited a quick (24 h) and long lasting (yolk‐sac absorption) significant over‐expression of measured heat shock proteins (hsps), all of which are known components of intracellular protein repair and stabilization mechanism. Thermal sensitivity, as indicated by the incidence of abnormalities and expression of different hsps, varied significantly between crosses. Thermally tolerant progeny exhibited a short but rapid hsp72 (size in kDa) over‐expression, and more pronounced hsp60 and hsp90 over‐expression, than less tolerant progeny which exhibited a prolonged hsp72 and hsp78 over‐expression. At environmentally relevant water temperatures bent larvae exhibited spiral swimming, which in the wild would compromise the ability of emerging larvae to forage, avoid predators, and migrate downstream, ultimately compromising survival and recruitment. Before larvae hsp content can be used as a thermal‐stress biomarker for GS, field validation studies are needed.     

Biologische Beobachtungen bei der Aufzucht von Heringsbrut

Zusammenfassung Im Frühjahr und Sommer 1960 wurden auf Helgoland die Aufzuchtversuche an Heringsbrut wieder aufgenommen. Als Elterntiere dienten Frühjahrslaicher aus der Elbmündung und der Kieler Bucht und eine Kreuzung Kieler Hering × Clyde-Hering.Erbrütung und Aufzucht erfolgten vornehmlich in kleinen Steinzeug-Bekken (120 1) mit Seewasserdurchfluß in einem temperaturkonstanten Raum mit diffuser, künstlicher Beleuchtung. Bei den Temperaturversuchen wurde die Brut bis zur Resorption des Dotters bei ca. 5°, 8°, 11° und 14° C gehalten. Später wurde in allen Becken die gleiche Temperatur angestrebt, die in den folgenden Monaten von 8° auf 14°C anstieg.Bei Verlassen des Eies waren die kalt erbrüteten Larven länger und verfügten über weniger Dotter als die warm erbrüteten. Am Ende des Dottersackstadiums hatten aber die bei 8°C gehaltenen Larven die größte Körperlänge erreicht.In einer weiteren Versuchsserie wurde die Brut gleicher, konstanter Temperatur, aber verschiedenem Salzgehalt ausgesetzt. Die bei 15, d.h. unter annähernd isotonischen Bedingungen gehaltenen Larven waren sowohl beim Schlüpfen als auch am Ende des Dottersackstadiums am längsten. Bei hohen Temperaturen (> 11°C) war die Schlüpfrate der Eier stark herabgesetzt. Die optimale Befruchtungs- und Schlüpfrate der Brut des Küstenherings lag im Gegensatz zum Nordsee-Bankhering im Bereich niedriger Salzgehalte (15 bis 20).Bezüglich der Größe und der Schlüpfrate konnten keine Unterschiede zwischen den Kiel × Kiel- und Kiel × Clyde-Larven festgestellt werden.Bei der Aufzucht traten zwei Phasen hoher Sterblichkeit auf. Die Mehrzahl der Larven starb bald nach der Resorption des Dotters, wahrscheinlich infolge unzureichender Ernährung. Die besten Überlebensraten wurden bei einem großen Angebot von frischgefangenem Zooplankton vermischt mitArtemia-Nauplien erzielt. Als weitere Todesursache junger Larven wurde das Auftreten von Gas im Darm beobachtet. Durch sorgfältige Beseitigung der Luftblasen von der Wasseroberfläche ließ sich diese Krankheit vermeiden.Nach einigen Wochen trat eine zweite Mortalitätsphase auf, der meist Larven von etwa 16–20 mm zum Opfer fielen. Die Anfälligkeit dieser Larven hängt vielleicht damit zusammen, daß bei ihnen die Kiemen noch nicht funktionstüchtig sind, das Verhältnis von Körpermasse zu -oberfläche aber immer ungünstiger wird.Etwa 5% der Larven überstanden auch diese Mortalitätsphase (0,1 bis 0,3% aller geschlüpften Larven), sie legten bei 25 mm Körperlänge Wirbel an und metamorphisierten, als sie 30–35 mm lang und 3–4 Monate alt waren. Trotz der hohen Verluste konnten die Versuche zeigen, daß es möglich ist, Heringslarven unter kontrollierten Bedingungen in kleinen Becken und bei künstlicher Beleuchtung bis zur Metamorphose aufzuziehen.Abschließend werden einige mögliche Verbesserungen in der Aufzuchttechnik genannt und die biologische Bedeutung der Konditionsunterschiede der Larven aus den verschiedenen Erbrütungsexperimenten kurz diskutiert.

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Summary Rearing experiments on herring were done using eggs and sperm from spring spawing herring of the Elbe estuary and Kiel Bight. A successful cross fertilization was also made between the eggs of a Kiel female and the sperm of a Scottish (Clyde) male herring, the sperm having been frozen for about six weeks.The eggs were incubated and the larvae reared at temperatures of about 5, 8, 11 and 14°C in 120 1 earthenware tanks with a sea water circulation, the apparatus being contained in a constant temperature room with artificial lighting. The temperatures were equalised in the tanks after the larvae had resorbed their yolk sacs and the temperature was then allowed to rise slowly from about 8°C to 15°C during the rearing phase.At high temperatures (greater than 11°C) the percentage hatching was much reduced. At hatching the larvae incubated at the lower temperatures tended to be longer and have less yolk than those larvae hatched at higher temperatures. At the end of the yolk sac stage the larvae kept at 8°C were longest.No differences in size or percentage hatching were observed between the Kiel × Clyde cross and its Kiel × Kiel control.In further experiments eggs and larvae were kept at a constant temperature but at different salinities. The highest percentage fertilization and hatching was found in a salinity of 15–20 (in contrast to that of North Sea Banks herring). The larvae were longest both at hatching and at the end of the yolk sac stage when kept in a salinity of 15 (isotonic conditions).There were two main phases of mortality during rearing. Most larvae died at the end of the yolk sac stage probably due to inadequate suitable food. The best survival was found in tanks where the larvae were fed on wild plankton andArtemia nauplii. Another cause of death was swallowing of air bubbles. This mortality was reduced by careful removal of air bubbles from the water surface and by keeping the surface very clean.After this initial phase of mortality there was good survival for some weeks until the larvae reached a length of 16–20 mm. The cause of death at this stage might have been due to respiratory difficulties caused by the gills not yet being functional and by the increasingly unfavourable relationship between body area and volume.About 5% of larvae which survived beyond the yolk sac stage (or 0,1 to 0,3% of hatched larvae) developed vertebrae at a length of 25 mm and metamorphosed when 30–35 mm long and 3–4 months old.These experiments show that it is possible to rear herring larvae to metamorphosis using controlled conditions in small tanks and with artificial light.Means of improving our rearing techniques are given and the biological implications of the differences in size of herring larvae reared under different conditions are discussed.

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(Mit 6 Abbildungen und 5 Tabellen im Text)

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Die Untersuchungen wurden ermöglicht durch Reisestipendien des Department of Agriculture and Fisheries of Scotland und des Bundesministeriums für Ernährung, Landwirtschaft und Forsten und durch Sachbeihilfen der Deutschen Wissenschaftlichen Kommission für Meeresforschung.     

Effect of temperature on fatty acid composition and development of unfed Siberian sturgeon (A. baerii) larvae

The fatty acid metabolism in fish is influenced by various factors, including fish species, water temperature, water environment and diet supply. The aim of present work is to investigate the fatty acid composition of yolk‐stage Siberian sturgeon larvae reared at three different temperatures. Fertilized Siberian sturgeon eggs were transferred to the Lodi Aquaculture Research Center of the University of Milan, divided in three aquaria, each containing three incubators and incubated at 16°C. After hatching the temperature was switched to 16, 19 and 22°C. Larvae sampling was performed at the end of yolk sac reabsorption. No feed was dispensed during the trial. Eggs and larvae were weighed and fatty acid profile was determined by GC‐FID analysis after lipid extraction by chloroform/methanol mixture and fatty acid transesterification by methanolic hydrogen chloride. The fertilized eggs had a weight of 23.27 mg and a lipid content of 2.67 mg/egg. At hatching, the weight was 12.2 (0.17 SD) mg and lipid content 1.9 (0.6 SD) mg/larva. At the end of the trial, larvae mean weight was 33.6 (3.6 SD), 34.7 (1.8 SD) and 36.9 (1.1 SD) mg, while lipid content was 2.0 (0.3 SD), 2.1 (0.3 SD) and 2.0 (0.2 SD) mg for larvae reared at 16, 19 and 22°C respectively, without statistically significant difference. Larvae subjected to the highest water temperature showed a faster yolk‐sac absorption. No differences were found across temperatures regarding survival rates and regarding ontogenic development. The fatty acid composition of larvae was affected by the temperature. Larvae reared at 16°C had the lowest amount of saturated fatty acids, mainly due to a lower palmitic acid content, that was offset by a higher level of linolenic and linoleic acid, if compared with larvae reared at 19°C and 22°C. The study suggests that at a lower temperature sturgeon spare unsaturated fatty acid consuming preferably saturated fatty acids, increasing our knowledge of the fatty acid metabolism in this species.     

Thermal effects in rainbow trout (Oncorhynchus mykiss) F1 embryos (farmed female × wild thermal-resistant male)

The aim of this work was to investigate the response of rainbow trout embryos (Oncorhynchus mykiss) (i.e., survival, size at hatching, time to hatching, malformations) to four incubation temperatures (5.8, 8.9, 14.0 and 16.8°C), taking into account the origin of the male parental genome and comparing pure farmed and F1 embryos (farmed female × wild thermal-resistant male). Several consequences of thermal stress were observed: lower accumulated thermal units (ATU) at hatching at high temperatures, and lower survival, shorter hatched free embryos and less-consumed yolk sac at extreme temperatures. The effect of the thermal-adapted male parental genome was shown only in the lower percentage of incompletely hatched free embryos in the F1 families. It appears that to obtain greater modification of thermal performance during early development, the adapted genome of the wild thermal-resistant population has to be included through maternal inheritance, thus producing a stabilized strain selected for domesticity, growth and thermal adaptation.     

Developmental fate of the yolk protein lipovitellin in embryos and larvae of winter flounder, Pleuronectes americanus.

The developmental fate of the vitellogenin-derived yolk protein, lipovitellin (Lv), was investigated in winter flounder embryos and yolk-sac larvae. Since Lv is present as only one major polypeptide in ovulated winter flounder eggs, unlike the multiple yolk polypeptides found in the mature eggs of most teleosts, this system is presented as a simpler model of yolk protein structure and utilization during teleostean development. Winter flounder Lv is cleaved during embryogenesis from a 94 kD polypeptide at fertilization to 67 kD and 26 kD polypeptides at hatching. The rate of this proteolytic processing is slow during early embryonic development, but enters a more rapid phase between days 8 and 12 post-fertilization in embryos reared at 4-5 degrees C, and approaches 50% completion at day 10. Lv processing is essentially complete 3 days before hatching; nevertheless, major degradation of the Lv peptide by the developing winter flounder does not occur until after hatching. The Stokes radius of Lv changes only moderately following processing, from 4.50 nm in unfertilized eggs to 4.19 nm in late embryos and newly hatched larvae, whereas the processed Lv retains its heat stability relative to other yolk polypeptides. Nearly 50% of its lipid content, however, is released from the Lv particle during embryogenesis, concomitant with cleavage of the Lv 94 kD polypeptide. Lv processing may thus render a portion of the yolk protein-associated lipid more accessible to the developing embryo, whereas other yolk components are retained for later use by the winter flounder larva. Alternately, removal of lipid may lead to proteolytic vulnerability of the Lv polypeptide. In either case, only a portion of the lipid moiety of the Lv particle appears to play a significant nutritive role for the embryo, whereas its protein component is reserved for larval use. J. Exp. Zool. 284:686-695, 1999.     

Effects of ambient Lake Mohave temperatures on development,oxygen consumption,and hatching success of the razorback sucker

Synopsis Spawning of razorback suckers,Xyrauchen texanus, in Lake Mohave occurred from 10–22°C and larvae were collected at water temperatures from 10–15°C in 1982 and 1983. In the laboratory, hatching success was similar from 12–20°C, but reduced hatching success was found at 10°C while none hatched a 8°C. Development rate and oxygen consumption were positively related to incubation temperature. Direct effects of ambient Lake Mohave water temperatures on hatching success of razorback sucker embryos are considered minimal. Historical spawning temperatures for the species are hypothesized based upon successful incubation temperatures and comparison to the white sucker,Catostomus commersoni.     

Lactate dehydrogenase ontogeny,paternal gene activation,and tetramer assembly in embryos of brook trout,lake trout,and their hybrids

Measurement of lactate dehydrogenase in reciprocal hybrids of trout during development revealed that a maternal effect was involved in the regulation of enzyme levels until resorption of the yolk sac was completed. Malate dehydrogenase specific activities were the same in these embryos and larvae. The more negatively charged B subunits of LDH predominated during early stages of embryogenesis in lake trout and brook trout with an increase in synthesis of A subunits evident as development progressed. Activation of the paternal A gene in reciprocal hybrids occurred at a relatively late stage with the LDH subunit specific to the retina appearing after hatching. Analysis of brook trout progeny from a cross of parental types with a variant and wild-type B subunit suggested nonrandom LDH tetramer assembly which may be genetically controlled.This study was supported by National Science Foundation Grant GB-7271.     

Isolation and characterization ofgrandchildless-like mutants inDrosophila melanogaster

Summary Two temperature-sensitive sex-linkedgrandchildless (gs)-like mutations (gs(1)N26 andgs(1)N441) were induced by ethylmethane sulphonate inDrosophila melanogaster. They complemented each other and mapped at two different loci (1–33.8±0.7 forgs(1)N26 and 1–39.6±1.7 forgs(1)N441), which were not identical to those of any of thegs-like mutants reported in earlier work.Homozygous females of the newly isolated mutants produced eggs that were unable to form pole cells and developed into agametic adults. Competence of the embryos to form pole cells was not restored by wild-type sperm in either mutant; that is, the sterility caused by these mutations is controlled by a maternal effect.Fecundity and fertility ofgs(1)N26 females were low, and their male offspring showed a higher mortality than that of female offspring, causing an abnormal sex ratio. The frequency of agametic progeny was 93.1% and 55.8%, when the female parents were reared at 25° C and 18° C, respectively. In eggs produced by thegs(1)N26 females reared at 25° C, the migration of nuclei to the posterior pole was abnormal, and almost no pole cell formation occurred in these egg. Furthermore, half of these eggs failed to cellularize at the posterior pole. When the females were reared at 18° C, almost all of the eggs underwent complete blastoderm formation, and in half of these blastoderm embryos normal pole cells were formed.In the other mutant,gs(1)N441, the fecundity and fertility of the females were normal. The agametic frequency in the progeny was 70.8% and 18.6% when the female parents were reared at 25° C and 18° C, respectively. In the eggs laid by females reared either at 25° C or at 18° C, the migration of nuclei to the periphery and cellularization proceeded normally; nevertheless, in the majority of the embryos no pole cell formation occured at the stage when nuclei penetrated into the periplasm. When the females were reared at 18° C, some of the embryos from these females formed some round blastoderm cells with cytologically recognizable polar granules and nuclear bodies, which are attributes of pole cells. The temperature sensitive period ofgs(1)N441 was estimated to extend from stage 9 to 13 of King's stages of oogenesis.     

Effects of temperature, salinity, and air exposure on development of the estuarine pulmonate gastropod Amphibola crenata

The primitive pulmonate snail Amphibola crenata embeds embryos within a smooth mud collar on exposed estuarine mudflats in New Zealand. Development through hatching of free-swimming veliger larvae was monitored at 15 salinity and temperature combinations covering the range of 2-30 ppt salinity and 15-25 °C. The effect of exposure to air on developmental rate was also assessed. There were approximately 18,000 embryos in each egg collar. The total number of veligers released from standard-sized egg collar fragments varied with both temperature and salinity: embryonic survival was generally higher at 15 and 20 °C than at 25 °C; moreover, survival was generally highest at intermediate salinities, and greatly reduced at 2 ppt salinity regardless of temperature. Even at 2 ppt salinity, however, about one-third of embryos were able to develop successfully to hatching. Embryonic tolerance to low salinity was apparently a property of the embryos themselves, or of the surrounding egg capsules; there was no indication that the egg collars protected embryos from exposure to environmental stress. Mean hatching times ranged between 7 and 22 days, with reduced developmental rates both at lower temperature and lower salinity. At each salinity tested, developmental rate to hatching was similar at 20 and 25 °C. At 15 °C, time to hatching was approximately double that recorded at the two higher exposure temperatures. Exposing the egg collars to air for 6-9 h each day at 20 °C (20 ppt salinity) accelerated hatching by about 24 h, suggesting that developmental rate in this species is limited by the rates at which oxygen or wastes can diffuse into and from intact collars, respectively. Similarly, veligers from egg capsules that were artificially separated from egg collars at 20 °C developed faster than those within intact egg collars. The remarkable ability of embryos of A. crenata to hatch over such a wide range of temperatures and salinities, and to tolerate a considerable degree of exposure to air, explains the successful colonization of this species far up into New Zealand estuaries.     

Survival of Coregonus albula (L.) (Teleostei) embryos incubated at different thermal conditions

Eggs of Coregonus albula were incubated at constant temperatures: 1.1, 2.0, 2.9, 4.9, 6.6, 8.4, and 9.9 °C, and the percentage of normal hatch was 20.6, 11.8, 30.4, 61.0, 51.7, 32.6, and 14.6%, respectively. The lower and upper median tolerance limit (TL 50) defined as the interpolated temperature at which embryos survival to hatch was 50% of the highest response (61% at 4.9 °C) were 2.9 and 8.5 °C, respectively. The optimum temperature range delimited by lower and upper TL 75 was encompassed by 4.0 and 7.2 °C.Eggs of C. albula incubated at variable temperature in a commercial hatchery showed a very high survival (up to 76%). Similarly low survival observed during hatching of embryos at constant temperatures of 1.1 and 2.0 °C could be hightened (to about 90%) by raising the temperature in the beginning of hatching period. This phenomenon was utilized in the technique of delaying C. albula embryos' mass hatching for the purpose of synchronization in time of stocking the lakes with the time of appearence of good thermal and food conditions for C. albula larvae.The conception of the optimal thermal conditions for Coregoninae embryogenesis was developed as the course of incubation temperature, securing the highest survival rate during embryogenesis and also during the larval period.     

Quantitative observations on the population ecology of Branchiura sowerbyi (Oligochaeta,Tubificidae)

Cohorts of Branchiura sowerbyi were reared at different temperatures and initial population densities in order to obtain data suitable for the interpretation of population dynamics in field populations. Percent hatching from cocoons reaches its maximum at 25 °C and decreases towards lower and higher temperatures. Embryonic development time, T_E, was measured and the relative threshold temperature, 10 °C, calculated by extrapolation. The degree day requirement for embryo development is 195 °C d. The time of first cocoon laying (T_gm) was observed and the ratio T_E/T_gm was seen to fit with that of other tubificid species cultured so far. Embryo mortality is rather high, while worm mortality is low or very low. Fecundity increases from 15 to 20 °C but decreases at 25 °C. A mathematical model for the simulation of population densities with four size-stage compartments is suggested. It could be used for the optimization of worm uptake (simulated as stage specific mortality) in mass cultures reared for the production of Branchiura, to be used as food for fish fingerlings.     

光照强度与光周期对虎斑乌贼胚胎发育的影响

为探究光照对虎斑乌贼受精卵孵化的影响,确定其胚胎发育的最佳光照条件,本研究采用单因子试验方法,分析了不同光照强度(10、30、50、70、90 μmol·m^-2·s^-1)和光周期L∶D(24 h∶0 h、18 h∶6 h、12 h∶12 h、6 h∶18 h、0 h∶24 h)对虎斑乌贼胚胎发育的影响.结果表明: 不同光照强度对虎斑乌贼胚胎发育的孵化率、卵黄囊断裂率、培育周期、初孵幼体体质量与胴长均影响显著;而对孵化周期和幼体出膜7 d后存活率无显著影响.其中孵化率、培育周期、初孵幼体体质量与胴长随着光照强度的增强先增大后减小,而卵黄囊断裂率则逐渐增大.最适光照强度为30 μmol·m^-2·s^-1,此光照强度下孵化率为(90.0±4.1)%,卵黄囊断裂率为(7.3±1.5)%,培育周期为(25.50±0.35) d,孵化周期为(8.10±0.89) d,初孵幼体体质量为(0.213±0.011) g,胴长为(1.013±0.022) cm,出膜7 d后存活率为(97.1±4.0)%.不同光周期对虎斑乌贼胚胎发育的孵化率、培育周期、孵化周期均影响显著,而对卵黄囊断裂率、初孵幼体体质量、胴长和幼体出膜7 d后存活率无显著影响.其中孵化率和孵化周期随着光照时间的增加呈现先增大后减小的变化.最适光周期为LD(12 h12 h),此光周期下孵化率达(88.7±1.8)%,卵黄囊断裂率为(8.7±1.8)%,培育周期为(25.00±0.50) d,孵化周期为(7.00±3.20) d,初孵幼体体质量为(0.209±0.005) g,胴长为(0.998±0.026) cm,出膜7 d后存活率为(96.8±7.1)%.说明弱光照强度30 μmol·m^-2·s^-1和半日光照强度L∶D(12 h∶12 h)更有利于虎斑乌贼的胚胎孵化.在实际生产中,应避免阳光直射,采取适当的遮光措施.     

Effects of temperature and moisture during incubation on carcass composition of hatchling snapping turtles (Chelydra serpentina)

Summary Flexible-shelled eggs of common snapping turtles (Chelydra serpentina) were incubated on each of two substrates (vermiculite, sand) at each of three temperatures (26.0°C, 28.5°C, 31.0°C) and three moisture regimes (wet, intermediate, dry). Embryos developing in cool, wet environments mobilized the largest amounts of protein from their yolk and attained the largest size before hatching, whereas turtles developing in warm, dry environments mobilized the smallest quantities of protein and were the smallest in body size at hatching. Embryos on wet substrates mobilized more lipid from their yolk than did embryos on dry media, but ambient temperature had no demonstrable influence on patterns of lipid mobilization. The total reserve of neutral lipid available in residual yolk plus carcass to sustain neonates in the interval prior to the beginning of feeding was largest in hatchlings from dry environments and smallest in animals from wet environments, but was unaffected by temperature during incubation. Hydration of tissues in hatchlings was higher when incubation was in cool, moist conditions than when incubation was in warm, dry settings, thereby indicating that some of the effects of moisture and temperature on mobilization of nutrients by embryos may be mediated by differences in intracellular water. Patterns of response to temperature and moisture recorded for turtles emerging from eggs on sand were similar to those recorded for hatchlings on vermiculite, so no important conclusion would have been affected by incubating eggs on one medium instead of the other.