Influence of salinity on eggs,sperm and larvae of low-vertebral herring reproducing in the coastal waters of the Soviet Union

Clupea harengus pallasi deposit their eggs in the coastal zone, which is the most dynamic part of the sea in respect to its regime. Salimity is one of the most variable factors on the spawning grounds. Observations were made in the seas of the European North and Far East, and in experiments where salinities varied from 0 to 70. Study of the influence of salinity on the development of sea herring eggs is of interest for several reasons. Firstly, salinity fluctuation patterns differ in different parts of a given habitat. In each area inhabited, salinity boundaries exist within which eggs can develop normally. Secondly, the levels of limiting salinities on spawning grounds differ noticeably in different seas. Hence, attention was paid to population-specific differences in the responses of eggs to salinity. Finally, detailed knowledge on the responses of sexual cells to low-salinity conditions helps to elucidate the ecological situation in areas with reduced salinity, and the reproductive potential of the population considered. Sexual cells of numerous populations of Pacific herring are capable of fertilization over a wide range of salinities. Fertilizability in low salinities and, partially, also in high salinities, reveals a population specificity. The responses of the eggs ofC. harengus pallasi to reduced salinities differ from those ofC. harengus harengus. Osmotic resistance of eggs to low salinities is considerably higher in the first-mentioned subspecies. Under salinity stress, eggs reveal individual differences which are not seen under optimum conditions of salinity. In all populations studied, responses to salinity change during embryology.     

Growth,production and energy transformations in the salt-marsh killifish Fundulus heteroclitus

Populations of Fundulus heteroclitus (L.) at the beginning of a growth season in a New England salt marsh consist of 3 yearly age classes, with the 1-year-old class contributing most of the biomass. Calculation of production rates revealed that the young fish were the most active part of the population and that females were more productive than males. The entire population spent equal amounts of energy in growth and in metabolism. Including the young of the year, we obtained total production of 160 kg dry weight/ha, a value among the highest obtained for natural fish populations. About 5 to 15% of the production is available to predators. Rates of food consumption by F. heteroclitus are high enough to turn over the population of prey relatively often. Popululations of F. heteroclitus are thus capable of exerting an important influence on the abundance and distribution of their prey.Contribution No. 3721 from the Woods Hole Oceanographic Institution.     

Tidal and diurnal influence on food consumption of a salt marsh killifish Fundulus heteroclitus

Feeding patterns during four 24-h periods, sampled at 3-h intervals, were investigated for the mummichog Fundulus heteroclitus, in a Delaware, USA tidal marsh. Two factors potentially influencing feeding patterns, time of day and tide height, were examined. On 2 of the sampling periods a low tide occurred in the morning, while on the other 2 sampling periods a high tide occurred in the morning. Results are reported as g-dry wt. of food per g-dry wt. of fish. F. heteroclitus is primarily a daytime feeder that most actively feeds at high tide, regardless of whether or not the high tide inundates marsh surface areas. When tide height was sufficient to inundate the marsh surface, fish invaded these areas and consumed prey characteristic of the marsh surface. F. heteroclitus is an important link in energy transfers between the marsh surface and subtidal systems, enhancing its own energy supplies by consuming marsh surface prey whenever available.     

Predator avoidance and school size in a cyprinodontid fish,the banded killifish (Fundulus diaphanus Lesueur)

Summary Solitary and schooling banded killifish (Fundulus diaphanus Lesueur) were attacked with a fish predator model in the littoral zone of a lake and their flight reaction distance to the model recorded. Reaction distance of solitary fish did not differ significantly from that of schooling fish, which was statistically constant over a wide range of observed school sizes. The results fo not support the proposed early predator warning function of social groups, which predicts an asymptotically increasing flight reaction distance with increasing group size. However, fish in larger and safer groups may detect an approaching predator sooner but delay their flight response, thereby permitting their individual members to spend more time assessing the nature of the threat before escaping. Such a strategy would reduce costly false alarms. Relative variation in recorded reaction distances was correlated negatively with school size, suggesting that schooling reduces variability in latency time to escape predators. This may be evidence for the above behavioural strategy. Further, the speed of transmission of the flight response within the school greatly exceeded the speed of approach of the predator model. This phenomenon enables schooling individuals to initiate avoidance behaviour before the approaching predator can be detected and before it reaches them.     

Methylmercury tolerance of killifish (Fundulus heteroclitus) embryos from a polluted vs non-polluted environment

We have previously found great differences in susceptibility to methylmercury (meHg) among batches of eggs produced by different females. This study compares the range and distribution of susceptibility in two populations of killifish, one from a creek in Montauk, New York, USA a rather pristine area, the other from Pile's Creek in Linden, New Jersey, an area heavily impacted by metal and oil pollution. After treatment with 0.05 ppm meHg, the distribution of craniofacial defects in embryos of the Montauk population ranged from very tolerant to very susceptible. The distribution of cardiovascular defects also ranged from very tolerant to very susceptible. Skeletal defects were prevalent in most batches of eggs. However, in the Pile's Creek population, very few females produced susceptible eggs, and most batches were tolerant with respect to the three types of malformations, especially the craniofacial defects. The ability to adapt to pollution is one reason that this species has remained abundant in such a highly polluted area. The ability of some species to adapt to chronic pollution by developing tolerance is a phenomenon that should be considered in choosing organisms for routine bioassay procedures, since the results will depend on the degree to which the population has become tolerant to the toxicant.     

The combined effects of salinity and temperature on larvae of the mussel Mytilus edulis

The combined effects of salinity and temperature on survival and growth of larvae of the mussel Mytilus edulis (L.) were studied. The effects of salinity and temperature are significantly related only as the limits of tolerance of either factor are approached. Survival of larvae at salinities from 15 to 40 is uniformly good (70% or better) at temperatures from 5° to 20°C, but is reduced drastically at 25 °C, particularly at high (40) and low (20) salinities. Larval growth is rapid at a temperature of 15 °C in salinities from 25 to 35, at 20 °C in salinities from 20 to 35. Optimum growth occurs at 20 °C in salinities from 25 to 30. Growth decreases both at 25° and 10 °C; the decline is most drastic at high (40) and low (20) salinities.Part of a study completed at the Bureau of Commercial Fisheries, Biological Laboratory, Milford, Connecticut, USA, while on a UNESCO Fellowship.     

Energy substrates for eggs and prefeeding larvae of the dolphinCoryphaena hippurus

Changes in the chemical composition of developing dolphin (Coryphaena hippurus) eggs and prefeeding yolksac larvae were determined in order to estimate probable dietary requirements of first-feeding larvae. Daily dry matter, protein nitrogen (PN), non-protein nitrogen (NPN), lipid, gross energy content, fatty acid and amino acid profiles from Day 1 to Day 2 eggs and Day 1 to Day 3 larvae were compared. Lipid was the primary endogenous energy source accounting for the daily caloric deficit through both the egg and larval stages, except over the day of hatching. The catabolism of lipid by embryos (0.078 cal d^–1) was greater than that by yolksac larvae (0.036 cal d^–1). The higher demand for energy by embryos was related to a greater rate of protein synthesis during the egg stage. The ratio of PN:NPN increased during egg development without change in total nitrogen content, but was constant throughout the yolksac larvae period. The lipid content per embryo did not decrease over the hatching period (Day 2 to 3, postspawning). However, there was a loss in amino acid content not totally accounted for by sloughing of the chorion at hatching. This loss, as protein, accounted for 0.053 cal of gross energy, which represented 70% of the total estimated energy needs of the fish over this period. Loss of non-essential amino acids (25%) was higher than that of essential amino acids (13%). Proline and tyrosine accounted for 32% of the total loss of amino acids at this time. The only preferential use of fatty acids over any period was a small but significant drop in the content of C22:6n-3 prior to the onset of feeding (Day 5, postspawning). It is speculated that the pattern of energy-substrate use of first-feeding dolphin larvae will reflect the pattern of endogenous energy use during the egg and prefeeding yolksac larval stages. Diets or feeding regimens with lipid as the primary energy source, and containing a fatty acid profile similar to that of eggs or yolksac larvae, should be useful in culturing this species, at least during the early feeding stages.     

Interaction of genotype and salinity in larvae of the oyster Crassostrea virginica

Adult Crassostrea virginica were obtained from 4 populations and spawned in the laboratory. The larvae from the within-population crosses and the hybrid crosses were raised at 4 salinities. There were no significant differences in survival of the larvae between the populations. However, one set of hybrids did show overdominance in survival. There were genetic differences between the populations in growth rate, but the expression of the differences depended upon the salinity, i.e, there was significant genotype-environment interaction. There were expressions of nonadditive genetic effects in the hybrid crosses, but the direction and magnitude was dependent upon the salinity. There was as much difference between populations from the same estuary as there was between populations from geographically isolated populations.     

Preliminary observations on the circulatory system in eggs and early larvae of some teleostean fishes

Observations on the pattern of blood circulation in eggs and early larvae of Ambassis, Mugil, Dorosoma and Thrissocles species have been made. In the initial stages, the tubular heart lies on the left side, near the cephalic region. The anterior end of the heart lies near the snout. The posterior end is attached to a point mid-way between the orbits and auditory vesicles; the position of the anterior end is greatly influenced by the size of yolk. Initially, the tubular heart and dorsal aorta lie in a line. As a result of yolk absorption, the anterior end of the tubular heart gradually sinks to a position posterior to the attached end. Liquified yolk is circulated through the heart in early stages; blood corpuscles become apparent only in larvae. The heart-beat, which is initially irregular, gradually becomes regular as development progresses. In the initial stages the blood flows to the caudal and not to the cephalic region. The blood vessels are narrow, and the oval-shaped blood corpuscles must therefore pass through individually, with their long axes parallel to the passage. A definite capillary system is not evident. The blood vessels can dilate and contract when required.     

航道疏浚泥悬浮液对黑鲷胚胎的发育及仔鱼摄食生长的影响

采用静水试验法,温度在20℃左右,并保持试验用水溶解氧为饱和溶氧的60%,用疏浚泥悬浮液与过滤海水按等对数间距稀释成4个体积浓度水平(1:2、1:10、1:50、1:200),同时以过滤海水为对照组,每一个浓度组设3个平行样本,对人工养殖的黑鲷Spaptls macrocephalus鱼卵和仔鱼进行毒性试验.试验结果表明:疏浚泥悬浮液对鱼卵孵化有一定影响,但不显著.仔鱼的全长和体重的增长与悬浮液浓度的变化并无十分明显的对应关系,只有当水体中的悬浮液达到一定浓度时,才显现出对仔鱼生长的影响作用.在仔鱼摄食过程中,悬浮液对全长生长产生的抑制或影响作用不显著,但高浓度的悬浮液则对体重增长产生了一定的抑制性,不过这是一种短暂性的影响,随着时间的延长,其作用逐渐减弱或消失.     

Combined effects of temperature and salinity on embryos and larvae of the northern bay scallop Argopecten irradians irradians

The combined effects of temperature and salinity on embryonic development and on larval survival and growth to setting size of the northerm bay scallop Argopecten irradians irradians (Lamarck) were studied in the laboratory. A 6x6 complete factorial design was used; temperatures ranged from 10° to 35°C, at 5C° intervals, and salinities ranged from 10 to 35S, at 5S intervals. Response-surface contour diagrams were generated to provide estimates of conditions for optimal responses. Normal development of embryos occurred over a very narrow range of temperature and salinity. Survival of larvae occurred over a wider range of temperature and salinity than did embryonic development or growth of larvae. Satisfactory growth (>70% of the maximum observed value) occurred only at high temperature-high salinity conditions; optimal conditions for survival occurred at similar salinities, but at slightly lower temperatures. Temperatures of 35°C or greater and/or salinities of 10S or less were lethal for all life stages studied. Both salinity and temperature exerted significant effects on development and survival, but temperature was clearly the dominant factor influencing growth. It is suggested that northern bay scallop embryos and larvae be reared at their respective optimal temperature-salinity levels so as to increase efficiency of aquaculture operations.This paper is adapted from a thesis submitted to the College of Fisheries, University of Washington, in partial fulfillment of the requirements for the MS degree. This study was conducted at the NMFS Laboratory in Milford, Connecticut, USA     

Calanoid copepod eggs in sea-bottom muds. III. Effects of temperature,salinity and other factors on the hatching of resting eggs of Tortanus forcipatus

The “resting” eggs of a marine neritic copepod, Tortanus forcipatus Giesbrecht, recovered from sea-bottom sediment were hatched in the laboratory. Hatching occurred at temperatures of 13° to 30°C, no eggs hatched at 10°C. Temperatures around 25°C were found to be optimal for hatching, although the range of optimal temperatures for hatching was approximately 5°C lower in eggs stored for 14 to 15 months than in those stored for 1 to 2 months. A wide range of salinity, from 18 to 54%S, was favourable for hachting. Eggs failed to hatch within the sediment mud, which suggests that they are in a state of dormancy in the mud. Hatching was successful under both light and dark conditions.     

Water and salt balance of halibut eggs and larvae (Hippoglossus hippoglossus)

Eggs of halibut [Hippoglossus hippoglossus (L.)] have a negative buoyancy in sea water of 35 S, in contrast to eggs of most flatfish species. The cause of this was investigated. The osmolality of the yolk is 350–420 mOsm during embryonic development. This is within the range for marine teleost serum and for yolk of pelagic eggs. Concentrations of major inorganic ions are comparable with those of pelagic plaice eggs [Pleuronectes platessa (L.)]. The values for Na⁺, K⁺ and Cl^- are 6, 85, and 64 mmol · (1 H₂O)^-1 after fertilization, and at the time of hatching the corresponding values are 17, 11, and 80. Large amounts of other inorganic constitutents are excluded for osmotic reasons. Malfunction in the regulation of osmolality or of inorganic constituents is thus unlikely to be the cause of negative buoyancy. The relative dry weight of the chorion (egg shell) in halibut eggs is less than in several pelagic egg types, excluding the chorion as the main contributor of negative buoyancy. It is concluded that a high content of organic matter in the rest of the egg is the cause of the negative buoyancy.     

Vertical distribution of eggs and larvae ofEngraulis encrasicolus in stratified waters of the western Mediterranean

The vertical distribution of the eggs and larvae of the European anchovy (Engraulis encrasicolus) in the western Mediterranean Sea in June 1984 and Agust 1985 was analyzed based on multiple plankton tows carried out at varying depths and using nets equipped with opening and closing mechanisms. Hydrographic parameters such as temperature, salinity, and chlorophylla were recorded simultaneously. Maximum abundance of anchovy eggs and larvae always occurred above the thermocline, even when maximum chlorophylla concentrations were located below the thermocline. Larval distribution appeared to be associated with the availability of suitable food organisms. As in other clupeoid species, the anchovy larvae carried out vertical migrations related to the photoperiod.     

Bioenergetics of ephyra larvae of the scyphozoan jellyfish Aurelia aurita in relation to temperature and salinity

The body mass of Aurelia aurita ephyrae was better correlated with the diameter of the central disc than with the distance between opposite rhopaliae or distance between opposite lappet tips. Body dry weight (y, in μg) related to the disc diameter (x, in mm) through the equation y = 22.33 x ^1.99. The exponent 1.99 was significantly lower than that for the medusa stage, indicating a tendency to grow in diameter rather than in weight through the ephyra stage. The average ash-free dry weight (AFDW) of ephyrae was 38.0% of the dry weight. The AFDW/diameter relationship was used to convert measured diameters to body AFDW and calculate succession in body mass, daily ration, daily growth rate and gross growth efficiency. Effects of temperature (6, 9.5, 12, 15 and 18 °C) and salinity (17.5, 22, 26, 30.5 and 35 PSU) on these parameters and feeding were studied at saturated prey concentration (222 Artemia nauplii l⁻¹ initial concentration) by daily measurements over 10 d. There was a strong effect of temperature for total ingestion, growth rate, growth efficiency and final body mass of individual ephyrae, whereas the daily ration was not significantly different between the different temperatures. The experimental group kept at the highest temperature (18 °C) diverged the most, and ephyrae at this temperature ingested 2.7 times more and increased in weight 5.4 times more than at 6 °C. The average daily growth rate and gross growth efficiency of these ephyrae were 34.5% and 25.1%, respectively, significantly higher than at 6, 9.5 and 15 °C. Significant effects of salinity were shown for total ingestion, daily ration, daily growth rate and final weight, although only total ingestion and daily ration diverged sufficiently to show effects in a post-hoc test. This test showed that total ingestion was significantly different for all salinities except between 22 and 35 PSU and between 17.5 and 26 PSU. The daily ration for 35 PSU diverged from all other salinities, whereas none of the other salinities showed any significant differences. Thus, provided food in excess A. aurita can double its weight every 2 to 4 d, dependent on temperature and can therefore develop to the medusa stage in short time. Differences in environmental salinity in the range 17.5 to 35 PSU have little or no effect on growth rate and growth efficiency, whereas our results indicate that the full seawater salinity (35 PSU) causes significantly higher ingestion rate compared to lower salinities. Received: 11 January 1999 / Accepted: 11 May 1999     

Behaviour of echinoid larvae around sharp haloclines: effects of the salinity gradient and dietary conditioning

We examined larval response to a range of sharp haloclines and determined the effect of dietary conditioning on that response in the sea urchins Echinometra lucunter and Arbacia punctulata. We reared larvae in the laboratory under a high or low concentration of either single (Isochrysis galbana) or mixed (Isochrysis galbana, Dunaliella tertiolecta, Thalassiosira weissflogii) microalgal species. For both species of sea urchins, rate of larval development was faster and age-specific larval length and width were greater in high-ration than low-ration diets. We examined the distribution of two- and four-arm larvae of E. lucunter from each diet treatment and of four-arm larvae of A. punctulata from the high-ration diets in cylinders with experimentally constructed haloclines. In three of the halocline treatments, the salinity of the bottom layer was 33‰ and that of the top layer was 21, 24 or 27‰ (21/33, 24/33 and 27/33) and in a fourth one, the salinities of the bottom and top layer were 30 and 21‰, respectively (21/30). The position of larvae in the cylinders varied with the steepness of the halocline and with dietary conditioning for both sea urchin species and all developmental stages tested. Significantly more larvae crossed the haloclines into water of 24 and 27‰ salinity than into water of 21‰ salinity. We observed an effect of diet on the position of larvae in the cylinders, and that effect varied among halocline treatments for both species. The proportion of larvae of E.lucunter that crossed the halocline was greater in low- than high-ration diets in the 24/33 and 27/33 treatments. Position of four-arm larvae in the cylinders also varied with food quality in high-ration diets: for E.lucunter in the 24/33 treatments, and for A. punctulata in the 21/30 treatments, more larvae from the single- than from the mixed-species diets were present above the halocline. Salinity in the adult habitat during most of the active reproductive period ranged from 15 to 40‰. We showed that larvae can respond to gradients in salinity, and therefore can remain within a water mass of higher salinity overlying the adult habitat. However, survival of poorly fed larvae may be increased if they are introduced into a new water mass and carried away from a nutritionally poor environment. Received: 9 July 1997 / Accepted: 12 January 1998     

Oxygen uptake and comparative energetics among eggs and larvae of three subtropical marine fishes

Oxygen uptake was measured and energy budgets were determined for eggs and larvae of bay anchovy (Anchoa mitchilli), sea bream (Archosargus rhomboidalis) and lined sole (Achirus lineatus). Using an energetics model, both minimum rations and prey levels were estimated. The Q_{O 2} [μl (mg dry wt)^-1 h^-1] increased approximately five-fold for all species during development from egg to feedingstage larvae. The weight exponents in power functions, R=aW^b, relating oxygen uptake (R) to dry weight (W) did not differ significantly among species. The exponents were: bay anchovy, 0.9770; sea bream, 0.8382; lined sole, 0.9416. Oxygen uptake was generally lower for bay achovy than for the other species. In the energy budgets issimilation efficiencies of all species were low (24–75%). Gross growth efficiencies ranged from 11–41%, and net growth efficiencies from 38–57%. An estimated 32–83% of ingested energy was excreted in feces and urine. The lavae used a relatively small proportion of ingested energy in metabolism (6–31%). The anchovy had the lowest assimilation and gross growth efficiencies, and the highest excretion rate. Consistent with the better growth and survival observed in previous experiments, sea bream were the most efficient assimilators and had the lowest required minimum rations. Required minimum prey levels for first-feeding larvae ranged from 400 copepod nauplii l^-1 for sea bream and bay anchovy to 1 000 l^-1 for lined sole. The estimated required prey levels were higher than levels at which significant survival had been observed.     

Free amino acids as energy substrate in developing eggs and larvae of the cod Gadus morhua

The content of free amino acids (FAA) in the cod (Gadus morhua L.) egg is about 200 nmol at spawning, decreasing by about 100 nmol/egg during the egg stage and about 75 nmol/larva during the yolksac larval stage. Together, alanine, leucine, serine, isoleucine, lysine, and valine account for about 75% of the decrease. Ammonium accumulates gradually during the egg stage and is quickly excreted after hatching. The body protein content is maintained during the egg and yolksac larval stages. The measured oxygen uptake of the cod embryo during the egg and yolksac larval stages accounts for about 85% of the oxygen necessary to catabolize the FAA disappearing during this period. Ammonia excretion of the cod embryo, as taken from literature data, is similar to the expected ammonia production from catabolism of the FAA. Our data suggest that FAA are a major substrate for aerobic energy production in cod eggs and yolksac larvae. The implication of this finding for the production of a favourable first-feed for cod and other cultivated marine fish larvae, and for the selection of high quality eggs of marine fishes, is stressed.     

Combined effects of temperature and salinity on the survival and growth of the larvae of Pandalus jordani (Decapoda: Pandalidae)

Survival and growth over an environmental range of temperature and salinities were examined in order to help assess the importance of these environmental factors in affecting the distribution, abundance and survival of larvae and provide greater understanding of factors affecting fluctuations in adult Pandalus jordani Rathbun population sizes. Larvae were shown to have a wide tolerance to salinity, especially in the early stages, but a relatively narrow tolerance to temperature. The optimal temperatures for survival, 8° to 11°C, were also optimal for growth as reflected by maximal growth increments and body size. It is therefore felt that fluctuations in temperature as seen within and between successive larval seasons would have profound effects on larval survival, growth rates and size at metamorphosis to the benthic juvenile phase.     

Influence of food concentration,temperature and salinity on the larval development ofBalanus amphitrite

Influence of food concentration (0.5, 1 and 2 x 10⁵ cell ml^–1 ofSkeletonema costatum), temperature (20 and 30°C) and salinity (15, 25 and 35) on the larval development ofBalanus amphitrite (Cirripedia: Thoracica) was examined. The mortality rate at 20°C was lower than at 30°C in general. Increase in food concentration from 0.5 to 1 x 105 cells ml^–1 improved the survival rate, but this was not evident when food concentration was increased to 2 x 105 cells ml^–1. The results indicate that food availability and temperature jointly determine the energy allocation for metamorphic progress. It was observed that the influence of the tested variables varied with instar. At 20 °C the mean duration of the second instar exceeded 3 d and was much longer than other instar durations. The fourth, fifth and sixth instars and the total naupliar period showed that the effect of different salinities at given food concentrations was negligible at 20°C, while at 30°C there was a marked decrease in duration with increasing salinity.