Maximum Hatching Research Articles

Preliminary trials on incubation of sablefish eggs ( Anoplopoma fimbria)

Incubation of sablefish eggs was investigated as part of a larger collaborative project on sablefish culture. Gametes of ripe adults, trap-caught, were transported separately to the laboratory in a cold chest at 3–4°C. Fertilizability of the eggs declined to 50% following 36 min immersion in 35‰ salinity sea water; under identical conditions sperm fertilization potential declined to 50% 1 min after addition of milt to sea water. From these data a fertilization procedure was developed that provided 85–90% egg fertilization. Under short-term “dry” storage (3–6°C), sperm motility remained high for 300–500 h; data on egg storage was not obtained. Fertilized, water-hardened eggs were 2.07–2.11 mm in diameter. From fertilization to hatching incubation times were obtained from 2.2 to 6.6°C; times to a number of embryonic stages were obtained from 3.6 to 7.9°C. The eggs are extremely fragile and easily damaged in culture. Percentage survival to hatching (20–35‰ salinity, 2.1–8°C) was 0–12.9%. Maximum survival to hatching occurred at salinities of 34–35‰ and temperatures of 4–6.6°C. Total length of larvae of few hours to several days after maximum hatch was 4.7–5.3 mm. Neutral buoyancy of developing eggs and larvae varied in a complex manner. From these data and related observations a model is presented indicating where developing eggs and larvae are likely to be found in the natural water column, a model that also could lead to the provision of oxygen requirements during the planktonic drift stages of egg and early larval development.

The combined effects of temperature and salinity on hatching success and the survival, growth, and development of the larval stages of Metapenaeus bennettae (Racek & Dall)

During the spawning season of the estuarine prawn Metapenaeus bennettae (Racek & Dall), laboratory and field experiments were conducted to examine the combined effects of temperature and salinity on hatching success of eggs and the survival, growth and development of larvae. Response surface analysis showed that optimal levels of temperature and salinity for maximum hatching success varied depending on conditions during spawning. Similarly, temperature and salinity conditions that produced maximum survival and growth of larvae depended on conditions during rearing prior to experimental temperature/salinity treatments. At the onset of feeding, larvae showed the lowest tolerance to changes in temperature and salinity. Supplementary feeding experiments in the laboratory, and survival rates in field experiments indicated that starvation was a more potent factor than the effects of temperature and salinity in determining survival through the protozoeal larval stages. Late larval stages were relatively indifferent to the effects of temperature and salinity. It is suggested that, during early development, adaptive response to the prevailing physical conditions enhances survival in an estuarine environment.

The biological response of the crayfish Procambarus clarkii to transplantation into California ricefields

The population dynamics of the crayfish Procambarus clarkii was studied in California ricefields to investigate the effects of range extension and to examine its potential for harvest. The species was shown to undergo distinct cycles of activity related to depth, temperature and reproduction. Juveniles were observed to have two peaks in activity during late summer and winter, while adults only had a single peak. Ovarian maturity was found during summer and maximum hatching occurred in late summer and winter. Males matured at 35.8 mm carapace length (CL) on the average, while females matured at 36.5 mm CL. A direct correlation between female egg production and body size was noted. P. clarkii in California were shown to be cued into similar cycles as Louisiana crayfish, even though the timing and extent of the hydrological cycle was considerably different. Breeding activity paralleled the Louisiana crayfish, while winter-spring juvenile growth rates (16.32 mm in 120 days) and biomass (208 kg/ha) were much lower. Crayfish emigration during ricefield draining was found to be substantial (31% of population) and may provide an excellent opportunity for harvest.

Comparison of Developmental Rate Curves Applied to Egg Hatching Data of Entomoscelis americana Brown (Coleoptera: Chrysomelidae)

Hatching of red turnip beetle, Entomoscelis americana Brown, eggs was studied at 13 constant temperatures (5–38.5°C). An average of 90% of the fertile eggs hatched from 10 to 36.5°C, indicating a broad optimal temperature range. The lower threshold and upper limit were near 5 and 38.5°C, respectively. The hatching rate (100 per mean no. h until hatching) was calculated for each temperature, and curves were fitted to the data using eight published equations describing the effect of constant temperatures on developmental rates of various insects. Five criteria are presented and used to evaluate the equations. An asymmetrical normal function satisfied the criteria better than the other equations and accurately described the effect of constant temperature on hatching rate for E. americana. Based on this equation, the maximum hatching rate was estimated to be 5.39% per h ± 0.15 (95% confidence interval) at the optimum temperature, 33.4 ± 0.58°C.

Marking of apricots by European red mite (Panonychus ulmi(Koch)) —a control programme

Abstract Observations in spring 1976 suggested that feeding by European red mite (Panonychus ulmi (Koch)) on ‘Moorpark’ apricot fruitlets was associated with the development of brown marks on the skin of the fruit. These marks, or feeding scars, detracted from the appearance of the fruit at harvest time. Trials carried out over the next 5 years not only confirmed the association but showed that the most effective treatment was carbophenothion (Trithion) applied at 58 g a.i. per 100 1 at the time of maximum hatch of winter eggs (mid October in Central Otago). Results also suggested that this treatment was beneficial even in the absence of mites. This spring treatment has proved to be more acceptable to growers than the autumn treatment recommended initially.

Effect of Temperature on Survival of Northern Pike Embryos and Yolk-sac Larvae

Abstract Experiments were conducted to examine the effect of water temperature and handling procedure on the percentage hatch of known-age northern pike (Esox lucius) embryos and on survival of the yolk-sac larvae. Embryos and larvae were incubated at constant temperatures from 3 to 24°C. The hatching temperature range was 3.1 to 20.9°C and lethal temperatures were 3 and 24°C. Optimum hatching range was 6.2 to 20.9°C and maximum hatch occurred at 9 to 15°C. The age of the embryo before temperature change and the test temperatures both had a significant effect on percentage hatch. Temperature had the greatest adverse effect on percentage hatch during the first 5 h of development. There was no significant difference in the number of embryos hatching when comparing those that developed for 5 h before temperature change with those that developed 12, 24, and 48 h before change. There was a significant increase in hatch for embryos that had developed 120 h before change. The type of temperaturxe change (shock o...

Temperature Requirements for the Survival and Early Development of the Anadromous Alewife

Abstract Studies were conducted to determine the effects of temperature on the hatching success of eggs of the alewife (Alosa pseudoharengus) and on the growth, survival, upper tolerance limit, and temperature preference of alewife larvae from the Hudson River. When eggs were incubated at seven constant temperatures ranging from 12.7 to 29.7°C, maximum hatching success occurred at 20.8°C. Hatching success fell significantly (P < 0.05) below the maximum when eggs were incubated at 26.7-26.8°C, and no hatch occurred at 29.7° C. The average time to median hatch varied inversely with temperature, ranging from 7.4 days at 12.7°C to 3 days at 23.8-23.9°C and 26.7-26.8°C. The upper tolerance limit of yolk-sac larvae acclimated to 14-15°C and exposed to elevated temperatures for 24 h was about 31°C. At seven constant temperatures ranging from 12.9 to 29.1°C, average daily rates of larval weight gain during the first 12 days after hatch increased with each higher temperature to a maximum of 83.8 µg/day (dry weight) at the highest rearing temperature (29.1°C). The maximum net biomass gain occurred at 26.4°C. The final preferendum of young alewives was estimated to be 26.3°C by monitoring their distribution in a thermal gradient during a 33-h period.

Responses of Largemouth Bass from Different Latitudes to Elevated Water Temperatures

The effects of elevated temperatures on largemouth bass Micropterus s. salmoides, from Minnesota and Wisconsin (our northern stock) and from Tennessee (our southern stock), were compared at four first-year life stages. Our purpose was to determine if data gathered from one part of a speciesˈ range could be used to set thermal standards for that same species elsewhere within its normal range. Eggs and embryos, when first exposed early in development to an array of elevated temperatures, lost 50% of their maximum hatching success (TL50) at 29.5 C for the northern stock and at 29.1 C for the southern stock. When embryos from the same pooled egg lots were exposed late in development, their TL50 temperatures were 32.3 C and 30.9 C, respectively. Median lethal 24-hour temperatures (TL50) for 0–3-day-old hatched larvae acclimated to 20, 24, 27, and 30 C averaged 32.1 C for the northern stock and 32.6 C for the southern stock. Median survival times for juveniles depended on acclimation temperature, exposure temperature, and the difference between these. Expected 24-hour TL50 temperatures, derived from median survival times, are 31.0 C for the northern stock and 30.6 C for the southern, based on 22 C acclimation. When fish were reared at temperatures from 28 to 35 C for 6 weeks growth rates were not significantly different among temperatures or between stocks. At 35 and 36 C for the northern and at 36 C for the southern stock, mortality rates were significantly elevated and net biomass gains were significantly depressed, although neither variable differed between stocks (P > 0.05). The differences between stock tolerances exceeded 1 C in only one of the elevated temperature challenges performed (1.4 C for the TL50 of late-exposed embyros) and neither stock was consistently more or less thermally tolerant. We conclude that, in terms of responses to elevated thermal challenges, M. s. salmoides is a thermally consistent subspecies over the latitudinal range represented by our samples. We further conclude that thermal standards for these fish may be based on data obtained from samples taken from any usual population within this range, provided a 2 C safety factor is used where TL50 data are involved.

Role of shell diffusion area in incubating eggs at simulated high altitude.

Embryonic development is inhibited when eggs are incubated at 9,100 m (0.3 atm) despite a normoxic environment. The problem apparently relates to respiratory gas exchange occurring by diffusion through gas-filled pores in the shell. Gaseous flux is therefore inversely proportional to ambient pressure and is affected by the physical characteristics of the ambient gas (Chapman-Enskog equation). Excess loss of H2O and CO2 occurs in eggs incubating at altitude and could be detrimental. Such increased loss should be correctable by decreasing diffusion area. This was tested by progressively increasing coverage of the shell with paraffin and incubating at simulated 0.3 ATA (225 Torr) in 100% O2. Uncoated eggs failed to hatch, but numbers of chicks increased with increased coverage. Maximum hatch was an extrapolated 90% of controls at 69% shell coverage. With further coverage, hatch size decreased. Egg weight loss, and estimate of H2O diffusion, was around three times controls in uncoated eggs but decreased linearly with paraffin coverage, reaching near normal at maximum hatch. Reduction of diffusion area to 0.3 normal at maximum hatch generally balanced the increased flux predicted for 0.3 ATA.

Zur fortpflanzungsbiologie von mesostoma ehrenbergii (Focke, 1836) (Turbellaria)

At room temperatures (20°C) no juvenile in resting eggs hatches from water. By combining room and refrigerator (3.5°C) temperatures the hatching rate increases to a maximum of 85%. To reach a hatching rate of 50–65% the influence of low temperatures must be at least 30 days. At room temperatures 60% of the young in resting eggs hatch from mud covered with water. Combining high and low temperatures the hatching success is between 67 and 81%, where the highest percentage of the young may hatch at room temperature. Up to 90 days low temperatures cause a maximum hatching rate of 79%. It decreases to approximately 30% after 180 days. At high temperatures resting eggs preserved in 100% moist mud, survive for two months. By adding a period of low temperatures the hatching rate increases to a maximum of 52%. Low temperatures are survived for more than 6 months. Up to 30 days preservation at 3.5°C causes a maximum hatching rate of 61%, up to 12o days it decreases to 30%. At room temperature the young in resting eggs are not resistant against air-dried mud (30–40% rel. air moisture). Combining high and low temperatures air-dried mud is endured 1 month (hatching rate 5–14%). Preservation of 30–120 days at 3.5°C and 70% rel. air moisture result in a hatching rate of 43–61%. li]4. In the open air in Middle-Europe there occur 5–6 generations of M. ehrenbergii per life-cycle. The first generation hatches from resting eggs in May, where the production of subitaneous eggs is independent on temperature. All other generations up to October hatch from subitaneous eggs. The egg-production of those worms is dependent on environmental factors. In summer subitaneous egg production prevails, in autumn resting egg production. The abundance during the life-cycle is dependent on the number of animals which produce subitaneous eggs. Resting eggs are predestinated to endure periods of dryness and cold. The life-cycles of the species M. lingua and M. productum are different from those of M. ehrenbergii in length and in the number of generations. In both species 7 generations occur over 8 to 8.5 respectively 5.5 months. M. nigrirostrum only forms resting eggs. The life-cycle consists of one generation from February/March to May/June.

White Sucker (Catostomus commersoni) Embryo Development, and Early Growth and Survival at Different Temperatures

White suckers (Catostomus commersoni) were exposed from fertilization through hatching to seven constant temperatures from 6.2 through 24.1 °C. High percentages of apparently normal larvae hatched at temperatures from 9.0 through 17.2 °C. Maximum percent hatch occurred at 15.2 °C, while only a few normal larvae were produced at 6.2 °C, and none at 24.1 °C.Growth rates increased from near zero at 10.0 °C to a maximum at 26.9 °C. At 29.7 °C growth fell below the maximum (P &lt; 0.05), and the incidence of spinal deformities was high. Death rates were uniformly low from 15.7 to 26.9 °C and were significantly higher at 10.0 and 29.7 °C (P &lt; 0.05). The rate of net biomass gain for test groups was maximum at 26.9 °C. Net rates of biomass gain declined progressively with temperatures below 26.9 °C until by 10.0 °C the rate of population growth became less than the rate of weight loss through deaths within the population. The temperature producing maximum hatching success, 15 °C, was nearly 12 °C lower than that providing for maximum growth and net biomass gain.Upper thermal 1-, 2-, and 7-day TL50 values for both newly hatched and swim-up larvae, when acclimated to 9 and 10 °C, were between 28 and 29 °C. When acclimated to 15 and 21 °C, they were between 30 and 32 °C.Lower 1-day TL50 temperature values for both groups of larvae acclimated to 21 °C were near 3 °C (&lt; 2.9), 2-day TL50 values were approximately 0.5 °C higher, and 7-day values were 4.8 °C for newly hatched larvae and 6.1 °C for swim-up larvae.

Early Development and Distribution of the Flathead Sole (Hippoglossoides elassodon)

Laboratory studies were conducted on eggs from a southern British Columbia population of Hippoglossoides elassodon. Salinity of neutral buoyancy of eggs decreased from about 25% shortly after fertilization to 17–18% at hatching. The incubation period ranged from 20.9 days (2.36–4.0 C) to 7.2 days (10.65 C). At temperatures of 5.5 C or lower and salinities of 19‰ or lower, larvae tended to hatch at a less advanced stage of development. Mean length of newly hatching larvae increased in successive periods throughout the hatching interval. At mean hatching time, larval length varied from 3.2 mm (15‰, 3.0 C) to 6.3 mm (25‰ 6 C). Larvae from eggs incubated over the range of test conditions (10.42–39.58‰, 2.36–10.65 C) reached a length of 6.9–7.2 mm at yolk exhaustion. Hatching success was highest in trials at 25‰, 6 and 7 C; maximum percent viable hatch is predicted at incubation conditions of 29.16‰, 7.38 C. Posthatching larval survival appeared normal at salinities of about 20–37‰ and temperatures of about 5.5 to &gt;10.65 C. Extensive early larval mortality occurred at salinities of 19‰ or less and at temperatures below 5.5 C. Incipient low lethal temperature levels are estimated to be near 3.5–4.0 C for incubating eggs and 4.0–4.5 C for larvae.Egg and larval characteristics of the experimental material were compared with similar data from the literature on North Pacific Ocean Hippoglossoides. A number of previous distinctions made between eggs and larvae of H. elassodon, H. robustus, and H. dubius require further validation owing to the possible confounding of genetic and environmental influences on the attributes studied. Distribution and abundance of H. elassodon over its North American range is discussed on the basis of the evidence gathered.

&lt;i&gt;In vitro&lt;/i&gt; study of factors related to the hatching of eggs of &lt;i&gt;Oesophagostomum columbianum&lt;/i&gt;

To determine the in vitro effects of various environmental and nutritional factors on the hatching of eggs, development and survival of larvae of Oesophagostomum columbianum, eggs were cultivated at different temperature gradients, humidity and PH in phosphate buffer saline (PBS), tap water (TW) and normal saline (NS) using serum and liver extract at different concentrations during the period from November 2008 to October 2009. In this study, no development of eggs was seen at 40C temperature within 15 days. The eggs also did not hatch while transferred to room temperature within 15 days. Hatching of eggs were maximum (38.7%) at 260C on day 5. While hatching of eggs of O. columbianum did not occur at pH 2. Maximum number of hatching of eggs was seen on day 6 (40.00%) at PH 6.5 and lowest in (3.65%) at PH 11.5. Maximum hatching of eggs (51.21%) were recorded in the relative humidity of ≥80%-90% on day 5. Light had no significant effect on the development and hatching of eggs of O. columbianum. Maximum eggs hatched in PBS containing 15% serum and 10% liver extract (42.16%) but for PBS containing 10% liver extract also produced about to same hatching rate (42.15%). The present study suggests that PBS containing 15% serum and 10% liver extract may be used as suitable media for the incubation of eggs of O. columbianum due to continuous increasing of hatching rate of eggs according to the advancement of days. Further more, for in vitro culture better results may be obtained if eggs are incubated at 260C, PH 6.5 and relative humidity ≥80%-90%. Keywords: O. columbianum; Factors; Hatching of eggs DOI: http://dx.doi.org/10.3329/jbau.v9i1.8744 JBAU 2011; 9(1): 55-60

Effect of temperature on hatching and viability of the eggs of Bunostomum trigonocephalum Rudolphi, 1808.

The effect of temperature on the hatching and viability of the eggs of Bunostomum trigonocephalum in a tropical climate is described. All experiments were performed with 500 eggs in each dish of saline medium. Experiments on hatching of eggs at any one temperature were repeated twelve times and on viability of eggs eight times.The range of temperature for hatching was found to be 10–34 °C. The time for commencement and for termination of hatching of eggs (in hours) was 18 and 48 at 34 °C, 21 and 51 at 30 °C, 24 and 54 at 25 °C, 45 and 78 at 20 °C, 77 and 119 at 15 °C, and 264 and 360 at 10 °C.The rate of hatching of eggs was observed at temperatures of 10, 15, 20, 25, 30 and 34 °C. Maximum hatching took place at 34 °C, which is also the optimum temperature for hatching. At a temperature of 10 °C, 98–99% of the eggs did not develop.The viability of eggs was observed at temperatures above and below the hatching range. Eggs remained viable up to 7 h at – 10 °C, 5 days at 0 °C, 7 days at 5 °C, 10 h at 35 °C, 6 h at 40 °C, 1 h at 45 °C, and 20 min at 50 °C.The authors wish to acknowledge a research grant from the Scientific Research Committee, Uttar Pradesh, India. We also express our thanks to Professor M. B. Lal for his kind encouragement and interest throughout this study.

The Influence of Soil Moisture On Survival and Hatch of Meloidogyne Javanica

Egg sacs do not appear to possess any marked powers of water retention; even at suctions of 50 cm of water there is a marked shrinkage of the egg sac and most of the water is removed at 200 cm of water suction. In an atmosphere of relative humidity 98% (equivalent to 28 × 103 cm of water suction) the percentage of second stage larvae in eggs increased from 7 to 45% in 5 days resulting in an increased rate of hatch when the egg sacs were placed in water. The egg sac matrix is an efficient barrier to water loss for the eggs contained inside. Eggs removed from the egg sac showed a marked decline in hatch in water after exposure to 98% R.H.; the experiment failed to demonstrate any difference in resistance to desiccation between eggs containing embryos and those containing second stage larvae. The level of the maximum hatch in glass beads decreases with decrease in size of the pores. It is suggested that eggs stop hatching when the pores empty because the egg sac shrinks thereby exerting a mechanical pressure on the egg shell and this factor plus the low hydraulic conductivity and the suction inhibit uptake of water by the egg. Swelling and distortion of the egg which are prerequisites for hatching are consequently inhibited. A hypothetical hatching curve in soil relating suction, soil moisture, crumb size and aeration is given.

Factors influencing the infectivity of plant parasitic nematodes

The influence of the host plant (tomato), temperature, pH , suction potential, osmotic potential and soil pore size on the hatch, mobility and invasion of the parasitic nematode Meloidogyne javanica were studied to try to define the conditions for maximum infection and to determine any characteristics of the nematode that increase its chances of invading the host. There are three phases of infection as defined in this paper: hatch, migration to the root, and invasion. The optimum temperature for hatching and for movement was about 25 to 30 °C and for invasion 20 to 30 °C. The optimum soil moisture for hatching, movement and invasion was in the region of field capacity when most of the larger pores have drained of water. The optimum pore size for movement and invasion was about 75 to 120 μm. Pores of this size range occur in coarse-textured soils, e. g. sandy loams. Osmotic potential and pH probably have only a minor influence on infection in soil. In water and sterile soil the rate of hatch was high, whereas in non-sterile soil hatch was inhibited unless tomato plants were present. Hatch, therefore, reached a maximum in soil only in the presence of a host plant, thereby increasing the chances of infection. The conditions for maximum hatch, movement, and invasion are similar, so when an egg does hatch it is in an environment conducive to rapid migration to the root and to quick invasion. Larvae were found to be infective for a limited time, 4 to 8 days, in these experiments. There was a visible depletion in food reserves during this time. It is suggested that as soon as the larva hatches and begins to migrate through the soil its sources of energy (food reserves) are used up, so after a time the nematode is unable to generate sufficient propulsive force to penetrate the root. Percentage infection decreased with nematode density. There was no lack of space for movement around the root but observations and measurements of invasion with single roots on agar indicated that there were at least six possible factors related to nematode density that influenced penetration: (1) multiple invasion, (2) increased attraction to roots following initial penetration, (3) shortage of space at the root tip, (4) destruction of root tissues and inhibition of root growth, (5) loss of attraction to roots when root growth stopped, (6) interference between individuals.

Effects of Salinity and Temperature on Embryonic Development of the Pacific Cod (Gadus macrocephalus)

Eggs of the Pacific cod (Gadus macrocephalus Tilesius) were held from fertilization to completion of hatching in various combinations of constant salinity (19–31‰) and temperature (2–10 C). Hatching occurred in all salinities and temperatures, and survival was highest at the lower levels of both factors. A direct and approximately linear relationship was found between rate of development and temperature within the temperature range employed. At each temperature the length of the incubation period was increased at lower salinities. It is suspected that eggs were subjected to hypoxial conditions in the experiments, a circumstance considered to have depressed survival rate over all experimental combinations. There was, in general, an inverse relationship between salinity and temperature with respect to both size of larvae produced and the duration of the hatching period. Calculated response isopleths suggest that eggs of Gadus macrocephalus are euryhaline, and that maximum hatching success may be found in the vicinity of 19‰ S and 5 C. Changes of 1 C were calculated to be equivalent in effect on hatching success to a change of about 12‰ S.

The incubation period of the eggs of Oncomelania nosophora.

SummaryThe incubation period of eggs of Oncomelania nosophora ranges from about 10 days to 35 days under seemingly uniform laboratory conditions. Maximum hatching occurred after 24–25 days at day time room temperatures of 20–25°C. in March–April, and at 18–19 days at 24–29°C. in May–June.

Studies on the non-parasitic stages of the cattle tick, Boophilus microplus (Canestrini) (AcarinaL Ixodidae)

Laboratory studies of the effects of temperature and relative humidity on the non-parasitic stages of the cattle tick, Boophilus microplus (Canestrini), are described. The pre-oviposition period ranged from 19-39 days at 59-60�F to 2-3 days at 97�F. The duration of oviposition was uninfluenced by relative humidity but varied from a maximum of 44 days at 59�F to a minimum of 4 days at 102�F. The minima at each temperature were exceedingly irregular, due to the deaths of ticks. The number of eggs laid by a female tick was uninfluenced by relative humidity. The peak oviposition mean of 2496 eggs per female occurred at 75�F, fewer eggs being laid at higher and lower temperatures. Daily egg output attained a maximum of 197 at 92�F, but was uninfluenced by relative humidity. The water loss of engorged female ticks was greatly affected by inert dusts and even dusting with a sample of soil chosen at random produced a significant increase in water loss. Developmental period was uninfluenced by order of deposition, but percentage hatch of eggs laid during the last few days of oviposition is lower. Eggs did not hatch at constant relative humidities lower than 70 per cent., but some were able to survive relative humidities lower than this if exposed periodically to a saturated atmosphere. The period of development of eggs varied from a maximum of 146 days at 62�F to a minimum of 14 days at 97�F. Maximum hatch occurred between 85 and 95�F, and at relative humidities above 95 per cent. Exposure of eggs to temperatures below the developmental zero prolonged the period of development merely by the period of exposure. Regular alternation of temperature between the limiting temperatures of 59 and 97�F with a steady rise or fall between the extremes resulted in development at a rate approximately equal to that obtained at constant temperature of 78�F, the arithmetic mean of the above figures. Larval longevity was influenced markedly by temperature and humidity. A maximum of 240 days was recorded at 72�F and 90 per cent. relative humidity. Larvae are able to recoup water losses sustained at low relative humidity by absorption from the atmosphere during subsequent periods of high relative humidity.

An Experiment in Hatching Silver Salmon (Oncorhynchus Kisutch) Eggs in Gravel

Abstract The eggs from five adult sea-run silver salmon (Oncorhynchus kisutch) were divided into two lots: 8,239 eggs were buried in gravel in a standard hatchery trough and 7,500 placed in a standard hatching basket as a control. Natural conditions were simulated as closely as possible with the gravel eggs. The eggs required 772.3 temperature units (t.u.) to maximum hatch (control), 1,084.3 t.u. to earliest emergence from the gravel, and 1,155.6 t.u. to maximum emergence from the gravel. Initial to final emergence required at least thirty-eight days. Of the eggs buried, 10.2 per cent emerged from the gravel. In the control, 65.9 per cent of the eggs hatched and 48.2 per cent survived to the time that the experimental fish had finished emerging from the gravel. Examination of the gravel and the dead eggs in it at the conclusion of the experiment and observations made during previous experiments support the view that silt carried by unusually severe floods smothered many of the eggs in the gravel. This fac...