A genetic analysis of early development in pink (Oncorhynchus gorbuscha) and chum salmon (Oncorhynchus keta) at three different temperatures

A factorial mating design was employed in which five males were mated to each of five females in each of two stocks for both pink and chum salmon. The resulting embryos and alevins were incubated at constant water temperatures of 4, 8, and 16 degrees C for pink salmon and 3, 8, and 15 degrees C for chum salmon. Variation among families in alevin and fry survival rates, hatching, button-up time, length, and weight was the least at 8 degrees C. Heritability of traits directly correlated with fitness, such as survival rates and button-up time, was low at all temperatures (h2 less than or equal to 0.25). Maternal effects could account for a substantial portion of the variation in alevin and fry size characters. Nonadditive genetic variance accounted for more of the variation in fry size characters than in those of alevins. Negative genetic correlations were observed between embryo survival and subsequent alevin size and between hatching time and subsequent alevin and fry size. Genotype-temperature interactions could underlie a substantial amount of phenotypic variation in the developmental characters examined for both species.     

Size‐dependent growth of individual Atlantic salmon Salmo salar alevins from hatch to first feeding

Variation in egg size, hatch timing and size at hatch, and their influence on individual growth rates of Atlantic salmon Salmo salar alevins up to first feeding were examined in pure strain and hybrid crosses of fish from Scotland and Canada. At the intra‐female, intra‐cross type and inter‐cross type levels, specific growth rates prior to first feed were strongly size dependent, with smaller and later hatching alevins growing significantly faster. The magnitude of this size‐dependent growth was greatest in the hybrid crosses. This resulted in a 40% reduction in the coefficient of variation (c.v. ) in alevin size from post‐hatch to first feeding at the intra‐female level, and a reduction of both intra‐ and inter‐cross differences in alevin sizes in the same period.     

Comparative developmental biology of pink salmon, Oncorhynchus gorbuscha, in southern British Columbia

Eggs and alevins from 21 families of pink salmon, Oncorhynchus gorbuscha , from five odd-year broodline stocks spawning in southern British Columbia were incubated under controlled water temperatures of 4° C, 8° C and 12° C. There were significant differences in egg survival among stocks and among families within stocks at all incubation temperatures, but the differences were greatest at 4° C. Alevin survival was at least 97% for each stock at each temperature. The most northern spawning stocks had higher egg survival at 4° C than did the others. Hatching time of the alevins and emergence time of the fry were similar for all five stocks. Alevins hatching at 8° C were longer than those hatching at 4°C or 12°C, but there were no stock differences in alevin length or tissue weight. Stocks with larger eggs produced alevins of greater total weight and more yolk. Emergent fry from Vancouver Island stocks had the greatest tissue weight at 12° C, but Fraser River fry were heaviest at 8° C. There were significant differences among families within stocks for alevin and fry size parameters, suggesting that family variation should be accounted for in studies of salmonid developmental biology.     

Influence of Inoculum Density,Host, and Low-temperature Period on Delayed Hatch of Meloidogyne javanica Eggs

Most eggs of M. javanica hatch within several days when incubated in water. Those that do not are said to show delayed hatching. Several experiments were conducted to determine the effect of specific conditions on the percentage of eggs with delayed hatch. Six initial inoculum densities ranging from 100 to 20,000 eggs per pot did not influence egg hatch within a 45-day incubation period. In a 60-day test, the percentage of eggs hatching after more than 20 days was low for egg masses removed from carrot and okra and high for those from pepper and bean. Increasing exposure to cold temperature (8 C) from 7 to 30 days tended to delay hatch.     

Survival data for dewatered Rainbow Trout (Salmo gairdneri Rich.) eggs and alevins

Survival of four intergravel development phases of rainbow trout, Salmo gairdneri Rich., in a dewatered environment varied with stage of development, duration of exposure, and relative humidity. Egg phases were considerably more tolerant than alevin phases. Cleavage eggs tolerated dewatering for 12 consecutive days (97% survival), the maximum period tested. Embryos tolerated dewatering until they began hatching on the eight day, when mortalities sharply increased. In contrast, eleutheroembryos had only 43% survival when dewatered 6h and pre-emergent alevins had only 36% survival when dewatered 2h. A few dewatered embryos died when relative humidity was 100%, but mortality increased significantly at 90 and 80% relative humidity. Survival of alevin phases, but not egg phases, in residual, non-flowing water was limited by formation of oxygen deficits.     

Cadmium uptake by rainbow trout, Salmo gairdneri eggs and alevins

The uptake of cadmium by eggs and alevins of rainbow trout from water concentrations of between 0.01 and 50.0 mg Cd 1⁻¹ was investigated. The cadmium content of eggs and alevins increased with time and with exposure concentration. Lower cadmium levels were detected in alevins than in eggs. Most of the cadmium (98%) in the eggs was found to be associated with the egg membrane or chorion. This explains the considerable reduction in cadmium concentration observed in alevins after hatching. Alevins hatching from eggs which had been exposed to cadmium survived longer in cadmium than alevins not exposed as eggs. This suggests that the pretreatment of eggs with cadmium serves some protective function. Behavioural and pathological signs of cadmium poisoning such as erratic swimming and blood clotting in alevins were observed.     

Ovipositional and ovicidal effects of the microbial agent Bacillus thuringiensis israelensis on Culex quinquefasciatus say (Diptera: Culicidae).

The magnitude of oviposition as well as the size, shape and the number of eggs per of egg rafts egg raft were determined after gravid Culex quinquefasciatus Say oviposited on water treated with water dispersible granules (WDG) of Bacillus thuringiensis ssp. israelensis (Bti) and on untreated water. The mean number of eggs/raft was lower in the treated than in the untreated water. Bti concentrations from 0.5 to 2.0mg/L affected the shape of egg rafts and number of eggs in each raft. As the concentration of Bti increased from 0.5 to 2.0 mg/L the shape of egg rafts became more irregular with fewer eggs in each raft. Exposure to Bti at 2- and 26-h reduced the hatching rates, and fewer eggs hatched at 26-h of exposure to Bti. As the concentration of Bti WDG increased from 0.5 to 2.0 mg/L, the hatching rate decreased. Eggs exposed for 2-h to 2.0mg/ L Bti had a hatch of 30% after 24 h, the rate increasing to 57% after 72 h. In contrast, in 26-h exposed eggs to 2.0 mg/L Bti, the hatching rate after 24 h was only 12% and this rate increased to 39% after 72 h. In larvae from eggs exposed for 2 h, the survival rate was 40% at 2.0 mg/L Bti and 87% in untreated controls. In contrast, the survival rates of larvae from 26-h exposed eggs was 91% in controls while it was 30% at 2.0 mg/L Bti. As the concentration of Bti increased from 0.5 to 2.0 mg/ 1 the survival rates of larvae decreased. The combined effects of reductions of egg rafts, low number of eggs per egg raft, and reduced hatching and survival rates could have significant cumulative effects on the yield of adult mosquitoes, and this could result in a greater control potential of this microbial agent.     

Genetic variation in survival of chinook salmon (Oncorhynchus tshawytscha) alevins exposed to an unidentified agent of mortality

Mortality of an unknown etiology occurs after hatching and before emergence among Harrison River chinook salmon (Oncorhynchus tshawytscha) alevins incubated in the Chehalis River Hatchery, British Columbia. Inter- and intra-stock genetic variation for alevin survival and time to death was investigated at Chehalis Hatchery in factorial crosses among chinook salmon from the Harrison and Capilano rivers. Alevin survival by family ranged from 0 to 100%, with a mean value of 35.2%. The mean family survival of pure Harrison alevins (13.0%) was significantly lower than that of Capilano alevins (64.1%). For the Harrison stock, estimates of the heritability of survival were 1.05 +/- 0.62 (sire component) and 0.03 +/- 0.07 (dam component). For the Capilano stock, the corresponding estimates were 0.79 +/- 0.53 and 0.80 +/- 0.54. Family means of time to death ranged from 7.5 to 48 days after exposure to mortality-inducing agents. The mean times to death for pure Harrison (15.3 days) and Capilano (21.8 days) families were not significantly different. Sire and dam component heritability estimates for time to death were high for the Harrison stock (1.39 +/- 0.87 and 0.71 +/- 0.46) but low for the Capilano stock (0.06 +/- 0.11 and 0.17 +/- 0.18). Values of survival and time to death for the reciprocal interstock hybrid alevins generally fell between those of the parental stocks. Neither survival nor time to death differed significantly between the reciprocal hybrids, but both traits were more strongly influenced by sire than by dam. The possibility of asynchronous paternal and maternal allele activation during embryonic development was proposed as an explanation for the strong paternal effects observed in this study.     

Individual‐level analysis of pre‐ and post first‐feed growth and development in Atlantic salmon

Atlantic salmon Salmo salar were followed from egg to smoltification using genetic analysis to identify individuals and to link observations from pre‐ and post first feeding. Egg size and hatch timing significantly influenced alevin size at first feed but neither egg size, hatch timing or alevin sizes were correlated to size, condition factor or smolt status post first feed. In a hatchery environment the potential advantage gained by early hatching, larger alevin does not persist after first feeding. Different physiological and genetic complexes appear to influence growth in these two distinct phases of the Atlantic salmon's life‐cycle.     

The effect of sodium and calcium concentrations on the hatching of eggs and the survival of the yolk sac fry of brown trout, Salmo trutta L. at low pH

The effect of various external concentrations of sodium and calcium on the survival and hatching of brown trout, Salmo trutta , eggs at pH 4.5 was tested. A calcium concentration of approximately 10 ppm (500 μE l⁻¹) enables freshly fertilized eggs to survive whereas eyed ova are tolerant of deionized water acidified by sulphuric acid with no other ions added. Concentrations of sodium and calcium of 1 ppm (44 and 50 μE l⁻¹, respectively) are sufficient to ensure the successful hatching of eyed ova and subsequent survival of the alevins. At pH 4.5 hatching is prolonged by the alevins passing through a temporary encapsulated stage.     

Cadmium toxicity to rainbow trout, Salmo gairdneri Richardson: a study of eggs and alevins

Cadmium toxicity to rainbow trout was evaluated at two cadmium concentrations (0.01, 0.10 mg1⁻¹) and in water without added cadmium using eggs reared through the larval (alevin) phase to swim-up fry. Exposure to 0.1 mg Cd 1⁻¹ promoted premature hatching, retarded growth, increased rates of mortality and the occurrence of developmental abnormalities such as spinal curvature and blood clots. Three methods of holding the eggs and alevins during the toxicity test were compared. Hatching time and success, alevin mortality, growth and development were not influenced by the method of containment but of the three methods, a subdivided perforated box system proved particularly useful for monitoring the responses of specific animals throughout the toxicity test.     

Racial differences in eggs and juveniles of Windermere charr, Salvelinus alpinus

At least four races of charr occur in Windermere, the largest natural lake in England: north basin and south basin autumn spawners, north basin and south basin spring spawners. This study examines racial differences between eggs and juveniles, and relates juvenile size and survival to egg size. There were no major differences between races for egg incubation times and the percentage of eggs hatching successfully, the latter being high (mean values 76–96%) with a negligible proportion of abnormal alevins (<0.8%). Although there were no significant differences in the lengths of the female parents, both eggs and alevins were significantly larger for the autumn spawners than the spring spawners. Size differences in alevins, especially live weight, were positively related to egg size but not female parent size. Mean percentage survival for juveniles attaining the independent feeding stage was higher for the progeny of autumn spawners (32%) than spring spawners (3%). Racial differences in the egg and alevin stages therefore appear to have a significant effect on subsequent survival, and could be ultimately responsible for the relatively small proportion of spring spawners (only 4–6%) in the Windermere population of charr.     

Temporal and spatial segregation of spawning in sympatric populations of Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L.

Based on data from Norwegian streams with sympatric populations of Atlantic salmon and brown trout, it is suggested that temporal segregation is the main mechanism segregating Atlantic salmon and brown trout during spawning. Peak spawning of trout was about 15 days earlier than that of salmon. Physical factors, such as water depth, water velocity and distance from the river banks segregate spawning sites of salmon and trout poorly. Gravel sizes of the redds of salmon and trout were significantly different, though with a considerable overlap, and mean egg depth of salmon and trout were 0.18 and 0.12 m, respectively, probably attributable to the different size of spawners of salmon and trout. None of the temporal or spatial parameters analysed segregate spawners of salmon and trout completely. Species determination of eggs and alevins from the redds showed no interspecific superimposition of redds. It is, therefore, concluded that low survival of hybrids after hatching does not explain the low frequency of hybrids observed in sympatric populations of salmon and trout.     

The effect of light intensity on the nightly movements of juvenile Atlantic salmon alevins away from the redd

Atlantic salmon ( Salmo salar ) alevins move away from the redd predominantly at night time, suggesting that light level is the controlling factor releasing activity. However, the exact relationship between Light level and alevin activity is unknown, so a series of artificial redds was used to monitor alevin movements under various night time incident light levels. Five experimental redds and two controls were run over a period of 3 years. Combining the results gave a significant negative correlation between the numbers of salmon alevins moving away from redds on light nights and light level. This behaviour was interpreted as a negative photoresponse since the frequency of alevin movement away from the redd was dependent on the light intensity. Two possible explanations as to why alevins may react in this way to light level were considered. Firstly, the behaviour could have evolved to ensure that alevins only move away from the redd when they are least likely to be caught by a predator or secondly, retinal developmental differences between alevins could have led to the observed behaviour.     

Toxic effects of zinc on fathead minnows Pimephales promelas in soft water

A fathead minnow life-cycle exposure to various zinc concentrations demonstrated that the most sensitive indicators of zinc toxicity were egg adhesiveness and fragility, which were significantly affected at 145 μg Zn 1⁻¹ and above, but were not affected at 78 μg Zn 1⁻¹ and below. These effects occurred shortly after the eggs were spawned (during water hardening) and therefore were not related to effects on the parental fish. Hatchability and survival of larvae were significantly reduced, and deformities at hatching were significantly increased at 295 ug Zn 1⁻¹ and above. Acclimated and unacclimated groups of larvae exposed to identical zinc concentrations for 8 weeks after hatch showed only slight differences in sensitivity.     

Preservation of rainbow trout (Oncorhynchus mykiss) eyed eggs using a perfluorochemical as an oxygen carrier

The objective of this study was to maintain the viability of chilled rainbow trout (Oncorhynchus mykiss) eyed eggs during storage using oxygenated perfluorochemical (PFC). Three trials were conducted using eggs at 161, 180 or 217 degree days (days from fertilization x incubation temperature in degrees C). A separate trial was conducted for 147 degree day eggs that were not at the eyed stage. For each trial, eggs were stored in a moisture-saturated atmosphere at 1 degrees C in PFC, water, and 1:1 combinations of PFC and PBS, PFC and 0.3 M glucose, PFC and mineral oil, or PFC and water. The PFC was oxygenated before each trial and all media were oxygenated at weekly intervals during the storage period. Eggs from each trial were also incubated without storage to provide Day 0 results. After 3 and 5 weeks of storage, eggs from each medium were incubated at 10 degrees C until hatch. Hatching percentage was expressed as a percentage of Day 0 results. The percentage of normal alevins that hatched was also determined. There were interactions (P < 0.01) between stage of development and treatment for hatching percentage after 3 and 5 weeks of storage. After 3 weeks of storage, eggs stored at 161, 180, or 217 degree days without PFC had hatching rates of 0-14.3% but eggs stored in any medium with PFC had hatching percentages from 75.1 to 106.4% of Day 0 values. After 5 weeks of storage, eggs stored at 161 degree days in PFC plus PBS or PFC plus water, and eggs stored at 217 degree days in PFC or PFC plus water, had higher (P < 0.05) hatching percentages than eggs stored in any of the other media. Eggs stored at 161 degree days for 5 weeks in PFC and water had a higher (P < 0.05) percentage of normal alevins hatching than eggs stored in PFC and PBS. Because of their early developmental stage, eggs stored at 147 degree days had low hatching percentages, except eggs stored for 3 weeks in PFC or PFC plus PBS. Chilling eyed eggs of rainbow trout to 1 degrees C and storing them in water with PFC as an oxygen carrier can preserve their viability for 5 weeks.     

Obituary of Vadim Dimitrovitch Vladykov, 1898–1986

Synopsis The behaviour and ecology of lake charr Salvelinus namaycush, brook charr S. fontinalis, and Atlantic salmon Salmo salar, are reviewed to assess the susceptibility of these species to mortality from exposure to episodic pH depressions and accompanying changes in water quality. Critical life history periods are identified from an examination of: spawning site characteristics, timing of acidic pulses, changes in the sensitivity of developing fish to acidic water, and the ability of these species to detect and avoid deleterious chemical conditions. The three species appeared to be most vulnerable to pH depressions during Snowmelt as: alevins emerging from the redd (brook charr); free embryos in the interstitial spaces of the spawning rubble (lake charr); and embryos during hatching and juveniles during smoltification (Atlantic salmon). Factors that may modify the toxic effects of or the behavioural responses to low pH included: water temperature, acclimation and body energy reserves. The effect of site-specific or episodic mortality of early life history stages on recruitment to the population could not be evaluated due to the lack of information on compensatory mechanisms.     

Effects of low environmental pH and temperature on hatching and metabolic rates in embryos of Anax junius drury (Odonata: Aeshnidae) and the role of hypoxia in the hatching process

• 1.1. Studies were conducted in order to determine the combined effects of low environmental pH and temperature on embryonic survival capacity and metabolic rates in the dragonfly, Anax junius Drury. Studies were also conducted to assess the effects of hypoxia on hatching success as well as to investigate the role of hypoxia as a possible physiological triggering mechanism for hatching.
• 2.2. At water temperatures of 10–30°C, an environmental pH value of 3.0 was extremely limiting and significantly reduced hatching success.
• 3.3. Over a pH range of 3.0–5.0, a water temperature of 30°C was found to be severely limiting. Over a pH range of 6.0–7.0, hatching success was greater than 80% at test temperatures ranging from 10 to 25°C.
• 4.4. Embryos of A. junius exhibited a greater tolerance to markedly low environmental pH (3.0) than that previously reported for fish and amphibians, although survival capacity was less than 10%.
• 5.5. An environmental pH value of 3.0 has a significant detrimental effect on embryonic development. Survivorship and developmental rate increase significantly over a pH range of 4.0–5.0.
• 6.6. Oxygen consumption rates were lowest for fertilized eggs exposed to a pH of 3.0 at all test temperatures (10–30°C). Metabolic rates increased significantly at pH 4.O.
• 7.7. Embryos hatch successfully under hypoxic conditions in both aqueous and nonaqueous media. Results suggest that hypoxia acts as a triggering mechanism for hatching in this aquatic insect.

     

Environmental induction of Na+ transporter affinity in Atlantic salmon embryos

Atlantic salmon ( Salmo salar L.) alevins hatched from eggs transferred from high- to low-Na water at 250° days, before the onset of the phase of increasing whole egg sodium content (at ∼380°days), showed a significantly reduced K _m for Na⁺ transport, whereas transfer at 400° days did not produce any change in K _m . Alevins hatched from eggs given acid shocks of 1, 3, 7 or 14 days duration initiated at 250 or 400° days showed no significant changes in Na⁺ transporter K _m . Extended acid exposure (38 days) from 250°days to hatching resulted in a slight lowering of K _m (P<0.05). A 24-day acid exposure from 400°days to hatching had no effect on Na⁺ transporter K _m . Alevins hatched from eggs incubated throughout in acidified water had a significantly reduced K _m compared to controls (P<0.01).
The timing and duration of periods of Na depletion of eggs is considered with respect to environmental induction of increased Na transporter affinity in teleost embryos as a mechanism of long-term physiological adaptation to the gradual acidification of natural waters.     

The effect of acid water on the hatching of salmonid eggs

The survival of salmon Salmo salar , sea trout and brown trout Salmo trutta eggs in acid water in the range pH 3·5±7·0 was investigated over a period of three winters. The effects of fertilising the eggs in acid water at pH 4·0, 4·5 and 5·0, and dilution of the test media were also studied. There was considerable yearly variation in the numbers of eggs which hatched, but there were no marked differences between the three species in the tolerances of the eggs to acid water; pH 3·5 was lethal within 10 days to all the eggs, but at pH 4·5 and higher pH levels there was no obvious difference in hatching attributable to acidity.