Egg Wet Weight Research Articles

Egg size does not universally predict embryonic resources and hatchling size across annual killifish species

Egg size has a crucial impact on the reproductive success of a mother and the performance of her offspring. It is therefore reasonable to employ egg size as a proxy for egg content when studying variation in offspring performance. Here, we tested species differences in allometries of several egg content parameters with egg area. We measured individual eggs in five species of annual killifish (Cyprinodontiformes), a group of fish where egg banks permit population survival over dry season. Apart from comparing allometric scaling exponents, amounts and compositions of egg components across the different species, we assessed the explanatory power of egg area for egg wet and dry weight and for hatchling size. We found notable species-specific allometries between egg area and the other egg parameters (egg dry weight and water content, elemental composition and triglyceride content). Across species, egg area predicted egg wet weight with highest power. Within species, coefficients of determination were largest in A. elongatus, a large piscivorous species with large eggs. Our study shows that systematically using egg area as a proxy of egg content between different species can ignore relevant species-specific differences and mask within-species variability in egg content.

Maternal size, not age, influences egg quality of a wild, protogynous coral reef fish Plectropomus leopardus

Maternal effects are widely known to influence early life-history traits of offspring, including egg and larval quality. We studied the relationships between maternal length, weight, age and hepatosomatic index, with indicators of egg quality (egg size, oil droplet size, total lipid content and lipid classes) of a wild, protogynous reef fish, the common coral trout Plectropomus leopardus. Of the egg wet weight, 3% was lipids, with the neutral lipids, triacylglycerol (34% of total lipids) and wax esters (40%), being the main source of lipid energy within the egg. Polar lipids comprised 24% of total lipid content. Egg size and oil droplet size increased positively with maternal weight, and egg size increased positively with maternal length (p < 0.05). None of the variation in total lipid or triacylglycerol content was explained by the maternal traits we examined, but the proportion of long-term storage lipid wax esters increased with maternal length and weight (p < 0.05). Maternal age had no effect on any indicators of egg quality. Hepatosomatic index influenced sterols, although only with fish weight (p < 0.01). Our study highlights the variability in egg characteristics of a protogynous fish in the wild, and provides a greater understanding of variation in maternal traits as indicators of egg quality for teleost fishes. Our results suggest that offspring from larger females may have an advantage during the critical transition to successful exogenous feeding through enhanced provisioning, and that size-truncation through fishing may have negative consequences for recruitment and replenishment of P. leopardus populations.

Comparative embryotoxicity of a pentabrominated diphenyl ether mixture to common terns (Sterna hirundo) and American kestrels (Falco sparverius)

Concentrations of polybrominated diphenyl ethers (PBDEs) in Forster’s tern (Sterna forsteri) eggs from San Francisco Bay have been reported to range up to 63μgg−1 lipid weight. This value exceeds the lowest-observed-adverse-effect level (1.8μgg−1 egg wet weight; ∼32μg−1 lipid weight) reported in an embryotoxicity study with American kestrels (Falco sparverius). As a surrogate for Forster’s terns, common tern (Sterna hirundo) eggs were treated by air cell injection with corn oil vehicle (control) or a commercial penta-BDE formulation (DE-71) at nominal concentrations of 0.2, 2, and 20μgg−1 egg. As a positive control, kestrel eggs received vehicle or 20μg DE-71g−1 egg. In terns, there were no effects of DE-71 on embryonic survival, and pipping or hatching success; however, treated eggs hatched later (0.44d) than controls. Organ weights, organ-to-body weight ratios, and bone lengths did not differ, and histopathological observations were unremarkable. Several measures of hepatic oxidative stress in hatchling terns were not affected by DE-71, although there was some evidence of oxidative DNA damage (8-hydroxy-deoxyguanosine; 8-OH-dG). Although DE-71 did not impair pipping and hatching of kestrels, it did result in a delay in hatch, shorter humerus length, and reduced total thyroid weight. Concentrations of oxidized glutathione, reduced glutathione, thiobarbituric acid reactive substances, and 8-OH-dG in liver were greater in DE-71-treated kestrels compared to controls. Our findings suggest common tern embryos, and perhaps other tern species, are less sensitive to PBDEs than kestrel embryos.

Biometrical relationships in developing eggs and neonates of Octopus vulgaris in relation to parental diet

Captive Octopus vulgaris adults were fed three mono-diets based on pilchard, crab and squid and allowed to grow until reproduction under controlled temperature. Spawns from each dietary treatment were isolated, and the embryonic development, egg length, width and wet weight, in addition to neonate dry weight, dorsal mantle length and ventral mantle length were monitored. Pilchard-diet spawns developed faster in terms of thermal time. Initial egg wet weight was higher for squid and crab diets. Irrespective of the parental diet, eggs passed through a swelling process so that egg width and wet weight increased in a nonlinear way, whereas egg length was left nearly unaffected. Egg length and initial wet weight showed a high correlation with neonate dry weight. Egg length, even at advanced incubation, can be used as a good proxy for neonate dry weight, this fact having potential implications for the ecological and aquaculture research on O. vulgaris.

Assessment of egg quality and realised fecundity of whiting Merlangius merlangus L. in captivity

Summary Potential predictors of egg quality were assessed in whiting Merlangius merlangus L. permitted to spawn in a tank from which eggs were collected. These included fertilisation rate, the proportion of viable buoyant eggs, egg diameter, and egg wet and dry weights; all were influenced by temporal effects and were negatively correlated with days from start of spawning. The spawning period was protracted, from February to June. Mean daily egg production per female was 2.74 ± 2.43 g and 2338 ± 2075 eggs, equivalent to 14.6 ± 13.1 g kg−1 day−1 female−1. Egg diameter was 1.21 ± 0.04 mm, egg wet weight 1.20 ± 0.21 mg, dry weight 0.10 ± 0.02 mg, and mean fertilisation rate and hatching rates were 76.8 and 73.3%, respectively. The incubation period ranged from 72 to 80 degree days and was dependent on temperature (x) and described by the equation y = 25.92 e−0.1219x. Realised fecundity was also assessed to determine if this gave a more accurate measure of reproductive potential, and this was compared with potential fecundity estimated from predictive regressions on fish length from fisheries data. Realised egg production of 20 females of 185 g mean weight and 256 mm fork length was 4 444 360 (95% CL 4 093 961–4 743 018), similar to predicted seasonal egg production based on gravimetric fecundity measurements of wild caught fish.

Reproductive performance and offspring quality of the first and the second brood of female swimming crab, Portunus trituberculatus

Although the swimming crab Portunus trituberculatus females can spawn up to 5 times during a reproductive season, only larvae hatched from the first brood are normally used for larval culture in commercial hatcheries. With the increasing price of swimming crab broodstock and decreasing availability of wild stock, there are increasing interests in the possible utilization of the second brood for larval culture. However, to date, no detailed study has been conducted to assess the reproductive performance and offspring quality from the second brood of female P. trituberculatus. The present study was conducted to compare reproductive performance and offspring quality of the first (1st) and the second brood (2nd) produced by female P. trituberculatus during a reproductive season. No significant differences in several important reproductive parameters, including percentage of females spawned, percentage of berried females successfully hatched, egg production per female and fecundity per unit body weight, was found between the first and the second brood. However, the first brood had significantly higher individual egg wet weight (1st = 40.54 µg; 2nd = 31.40 µg), egg dry weight (1st = 13.51 µg; 2nd = 10.55 µg) and hatchability (1st = 78.41%; 2nd = 66.04%), and significantly higher survival (1st = 88.31%; 2nd = 65.38%) and faster development (1st = 3.82 days; 2nd = 4.34 days) from zoea I to zoea II and showed better starvation resistance in newly hatched larvae (1st = 5.03 days; 2nd = 2.98 days) than the second brood ( P < 0.05). Furthermore, the newly hatched zoea I from the first brood also had significantly higher total lipids, 16:1 n− 7, 18:1 n− 9, threonine (Thr) and arginine (Arg) contents, but lower levels of 18:0 and histidine (His) ( P < 0.05) as compared to those of the second brood. These biochemical differences are likely linked to different larval quality of the first and the second brood.

Embryo and larva development in common dentex ( Dentex dentex), a pelagophil teleost: The quantitative composition of egg-free amino acids and their interrelations

Free amino acids (FAAs) play a key role in the physiology of marine teleosts (eggs, embryos, and larvae). However, the relationship between the egg FAAs content and the production of viable embryos and larvae (at different developmental stages) in batch spawner pelagophils has not yet comprehensively been investigated. Viable eggs of common dentex, Dentex dentex, were obtained from captive broodstocks. Egg wet weight (WW), dry weight (DW), and water content (%W) and viability parameters, or VPs (egg floating rate [FR], hatching rate [HR], and larval survival rate [SR] at days 0 to 5 posthatch) were determined for 45 egg batches. The egg batches were classified according to their HR magnitude. Twelve egg batches with the same WW, DW, and %W were taken from the same broodstock and at the same developmental stage to determine the qualitative and quantitative composition of FAAs. The total FAA (TFAA) content, glutamic acid (Glu), asparagine (Asn), glutamine (Gln), and arginine (Arg) were correlated with VPs. The Glu was significantly correlated with HR and SR at 0 day posthatch (dph), the Asn with SR at 1 dph, and the Gln and Arg with FR and HR. Of the 361 ratios made based on the absolute concentrations of FAAs, 24 ratios were correlated with VPs (P < 0.005) through 42 simple regression models (R 2 = 0.641 to 0.846). Of the 42 significant relationships found ∼10%, ∼28%, ∼12%, ∼30%, ∼8%, ∼4%, ∼2%, ∼2%, and ∼2% of the models show the relations of the egg FAAs ratios with FR, HR, SR at days 1 to 5 posthatch, and %W, respectively. A path coefficient in combination with a Pearson's correlation coefficient provided a series of statistical evidences to show the effects of the egg FAAs interrelations on the relationships found between quantitative composition of a FAA and a VP.

Reproductive traits of an estuarine crab, &lt;em&gt;Neohelice&lt;/em&gt; (= &lt;em&gt;Chasmagnathus&lt;/em&gt;) &lt;em&gt;granulata&lt;/em&gt; (Brachyura: Grapsoidea: Varunidae), in two contrasting habitats

Reproductive traits of an estuarine crab, Neohelice (= Chasmagnathus) granulata (Dana 1851), were compared between individuals living in contrasting habitats (mudflat and saltmarsh) of the same population in the brackish coastal lagoon of Mar Chiquita, Argentina. In both habitats, most measures of egg biomass decreased during embryogenesis, including total dry weight (DW) and organic matter (measured as ash-free dry weight, AFDW) per egg, the contents of ash, carbon, hydrogen and nitrogen (per egg and as percentage values of DW), the energy content (estimated from C; both per egg and per mg DW), and the C/N and C/H mass ratios. Egg size, wet weight (WW), and water content (in µg and % of WW), by contrast, increased significantly during the time of embryonic development. These parameters reached significantly higher final (near-to-hatching) values in mudflats than in saltmarshes (egg volume 0.0249 vs 0.0233 mm3; WW 36.5 vs 28.8 µg; water content 30.7 vs 23.2 µg per egg or 84.2 vs 80.2% of WW, respectively). Fecundity and reproductive effort did not differ significantly between habitats. Habitat-specific differences in the water content and size of crab eggs are discussed in relation to small-scale local variation in environmental conditions.

Photoactivated polycyclic aromatic hydrocarbon toxicity in medaka (Oryzias latipes) embryos: Relevance to environmental risk in contaminated sites

The hazard for photoactivated toxicity of polycyclic aromatic hydrocarbons (PAHs) has been clearly demonstrated; however, to our knowledge, the risk in contaminated systems has not been characterized. To address this question, a median lethal dose (LD50) for fluoranthene photoactivated toxicity in medaka (Orvzias latipes) embryos was determined experimentally and then compared with ultraviolet-A (UV-A; 320-400 nm) radiation exposures in a PAH-contaminated field site. The dose metric, J/cm2/ microg fluoranthene/g egg wet weight, provided the means to estimate risk as the depth where the LD50 level would be exceeded at realistic field PAH concentrations, based on estimates of UV-A exposure. The estimates were made using 30 years of solar radiation data for Duluth (MN, USA) and measurements of water-column UV-A transmittance in a PAH-contaminated field site. Medaka embryo failure was strongly related to tissue PAH concentration and UV-A exposure. The LD50 was estimated to be 12.64 J/cm2/ microg fluoranthene/g egg wet weight; the 95% confidence interval was 8.46 to 19.7 J/cm2/microg fluoranthene/g egg wet weight. Embryo failures were characterized by undifferentiated cell proliferation that occurred very early in development. No partial effects or embryo/larval malformations were observed. Estimates of the depth at which the LD50 would be exceeded in the contaminated field site ranged from 10.7 cm (clear-sky conditions and lowest attenuation) to 0.0 cm (cloudy conditions and highest attenuation). Similar calculations were done using water-column attenuation estimates from 12 sites across the Great Lakes (USA). For these, the depths at which the LD50 would be exceeded ranged from 0.00 to 271.6 cm under the conditions described above. These results suggest that PAH phototoxicity may be a risk factor in specific contaminated sites, and they provide a framework for assessing that risk.

Organochlorine contaminants in complete clutches of Morelet's crocodile (Crocodylus moreletii) eggs from Belize

Seven complete clutches of Morelet's crocodile (Crocodylus moreletii) eggs were collected in northern Belize and examined for organochlorine (OC) pesticide residues. The primary OC detected, p,p-DDE, was found in every egg analyzed (n=175). Other OCs detected included p,p-DDT, p,p-DDD, methoxychlor, aldrin, and endosulfan I. Concentrations of individual OCs ranged from 4ppb (ng chemical/g egg wet weight) to greater than 500ppb. A statistical evaluation of p,p-DDE levels in three complete clutches was used to derive the minimum number of eggs needed from a clutch to precisely determine the mean p,p-DDE concentration representative of that clutch. Sample sizes of 8 (80% confidence level) and 11 (90% confidence level) were determined to yield an accurate estimate of contaminant levels in a full clutch of eggs. The statistically recommended sample size of 11 eggs (at 90% confidence level) was successfully tested on the four additional clutches.

Determination of carotenoids and all- trans-retinol in fish eggs by liquid chromatography–electrospray ionization–tandem mass spectrometry

A novel method was developed for the combined determination of carotenoids and retinoids in fish eggs, which incorporates prior analyte isolation using liquid-liquid partitioning to minimize analyte degradation, and fraction analysis using high-performance liquid chromatography–electrospray (positive)–quadrupole mass spectrometry (LC–ESI(+)–MS; SIM or MRM modes). Eggs from Chinook salmon ( Oncorhynchus tshawytscha) were used as the model fish egg matrix. The methodology was assessed and validated for β-carotene, lutein, zeaxanthin, and β-cryptoxanthin (molecular ion radicals [ M] +), canthaxanthin and astaxanthin ([ M + Na] + adducts) and all- trans-retinol ([( M + H)–H 2O] +). Using replicate egg samples ( n = 5) spiked with β-cryptoxanthin and β-carotene before and after extraction, matrix-sourced ESI(+) enhancement was observed as evidenced by comparable %matrix effect and %process efficiency values for β-cryptoxanthin and β-carotene of 114–119%. In aquaculture-raised eggs from adult Chinook salmon astaxanthin, all- trans-retinol, lutein and canthaxanthin were identified and determined at concentrations of 4.12, 1.06, 0.12 and 0.45 μg/g (egg wet weight), respectively. To our knowledge, this is the first report on a method for LC–MS determination of carotenoids and retinoids in a fish egg matrix, and the first carotenoid-specific determination in any fish egg sample.

Effects of post-ovulatory oocyte ageing and temperature on egg quality and on the occurrence of triploid fry in rainbow trout, Oncorhynchus mykiss

The present experiment was designed to evaluate the effect of spawning season rearing temperature and post-ovulatory oocyte ageing on egg developmental success in rainbow trout, Oncorhynchus mykiss, assessed as percent survival at the eyeing, hatch and swim-up stages, and as percent occurrence of malformations and ploidy anomalies at yolk sac resorption. Moreover, female weight, egg wet weight, oocyte ATP concentration and ovarian fluid pH, osmolality and protein concentration were measured to investigate possible links with post-ovulatory oocyte ageing and egg developmental success. Thirty three mature females were held at 12 °C and 10 at 17 °C. Eggs and ovarian fluid were sampled at the time of detected ovulation and 1, 2 and 3 weeks later. Eggs were inseminated with fresh semen pooled from five males and embryo development was monitored until yolk sac resorption. Generally, survival rate decreased and malformation rate increased with an increase in post-ovulatory oocyte ageing. Egg developmental success was positively correlated to female weight and to ovarian fluid pH and osmolality. Ovarian fluid protein concentration significantly increased during post-ovulatory ageing, whereas oocyte ATP concentration remained constant. A significant increase in morphological anomalies was observed as soon as 7 days post-ovulation (dpo), though this effect was not correlated with decreased survival. Also, an increase in spontaneous triploidy was associated with increased post-ovulatory oocyte ageing and high temperature, sometimes in dramatically high proportions (50%).

Reproductive Abnormalities, Teratogenicity, and Developmental Problems in American Kestrels (Falco sparverius) Exposed to Polychlorinated Biphenyls

This study found abnormalities in multiple reproductive stages in captive American kestrels (Falco sparverius) when exposed to polychlorinated biphenyls (PCBs) through dietary and in ovo exposure. American kestrels laid eggs with environmentally relevant total PCB levels (34.1 μg/g whole egg wet weight) when consuming PCB-spiked (Aroclor 1248:1254:1260) food (5–7 μg/g body weight per day) for 100 d only in 1998. In 1999, the same adults laid eggs with estimated total PCBs of 23 μg/g. Effects of maternal (only female exposed) and paternal (only male expose d) in ovo PCB exposure were investigated. Maternal F1 eggs contained predicted total PCB concentrations of 0.34 μg/g. Specific abnormalities occurred more frequently during dietary F0 exposure, particularly aggressive courtship interactions, clutch abandonment, occurrences of cracked eggs, and developmental effects. Multiple developmental effects were more pronounced during than after dietary PCB exposure of adults, and although these effects were limited, nevertheless they occurred in the F1 maternal and F1 paternal pairs. However, the incidence of multiple deformities throughout the breeding season increased dramatically from 1998 (13%) to 1999 (56%) in F0 PCB-exposed pairs. Developmental abnormalities were unlikely to be attributed to the extrinsic factors of disease, genetics, or nutritional (vitamin D3) deficiencies, but rather to adverse changes in parental behavior and intrinsic factors involving altered genetic material and PCB exposure. Readily cleared PCB congeners may induce specific types of behavioral and developmental abnormalities, but persistent congeners and metabolites are likely producing (1) odd laying patterns, (2) developmental effects including embryonic underdevelopment and edema, and (3) increased incidences of multiple deformities within a clutch.

The relationship between egg size and female size infreshwater crayfish, Astacus leptodactylus

In crayfish reproduction, one of the main factors affecting fecundity is egg size (Corey, 1991). An increase in egg size causes a decrease in fecundity in fish, gammaridean amphipods and similarly in crayfish (Abrahamsson, 1971; Ware, 1975; Steele and Steele, 1991). Although the relationship between fecundity and female size of Astacus leptodactylus has been the subject of much investigation (Cherkashina, 1970; Kossakowski, 1971; Papadopol, 1975; Stypinska, 1979; Koksal, 1988; Harlioglu, 1996), the relationship between egg size and female size of A. leptodactylus is little known (Harlioglu, 1996). Only a few studies have been carried out on crayfish species to evaluate the relation between egg size and female size (Abrahamsson, 1971; Mason, 1978; Lahti and Lindqvist, 1983; Kuris, 1991; Harlioglu, 1996). In order to have an accurate fecundity estimate, which is used in the estimation of recruitment, in addition to the relation between egg number and female size, the relation between female size and egg size should also be considered. Therefore, in the present study, the relationship between egg size and female size, and between egg wet weight and female size in A. leptodactylus was investigated. Males and females of A. leptodactylus were transferred from their natural habitat, the Agin Region of Keban Dam Lake, to the Crayfish Reproduction Unit of the Aquaculture Faculty of Firat University in Cip, Elazig in late summer of 1998. Mating and spawning started in mid-January 1999, and took approximately 3 weeks. The crayfish samples (n = 55, size range = 37–58 mm

Population features of Microphrys bicornutus Latreille, 1825 (Brachyura, Majidae) from Isla Margarita, Venezuela

The aim of this study is to characterize the population biology (sex ratio, size structure, relative growth of reproductive characters and realised fecundity) of the crab Microphrys bicornutusfrom Isla Margarita, Venezuela. Nearly 100 crabs were collected and fixed monthly during 1998. In the laboratory, crabs were sexed and measured: maximum carapace length, chelae length, chelae and abdomen width for females and first pleopod length for males. Additionally, 96 ovigerous females were collected to determine fecundity. The following measurements were taken for each female: body wet weight (BWW), body dry weight (BDW), egg wet weight (EWW), egg dry weight (EDW) and number of eggs (NE). The following determinations were made: relative fecundity (RF) = NE/BDW and reproductive output (RO) = (EDW/ BDW) × 100. Relative size at the onset of maturity (RSOM) was calculated as minimum ovigerous female/female's maximum size. The results indicate that the sex ratio is nearly 1:1 during the entire year. Ovigerous females and moulted males and females were observed throughout the year. Size frequency distribution and size at the onset of sexual maturity, estimated by relative growth of the sexual secondary characters and RSOM value, differed from those estimated in studies done in Jamaica and Buchuaco, Venezuela.

Embryonic ecdysteroids in a mole crab,Emerita asiatica (Milne-Edwards)

Using radioimmunoassay (RIA) and high performance liquid chromatography (HPLC), the presence of a complex mixture of free and conjugated ecdysteroids is reported in the embryonated eggs of a mole crab,Emerita asiatica. From an initial low value of 6.5 ng/g egg wet weight in stage I, the total ecdysteroids increased in concentration to 15.2 ng/g egg wet weight in stage III. This was followed by a sharp fall in stage IV, but again increased to 15.0 ng/g egg wet weight in stage VI. After a further decline in stage VII, the total ecdysteroids registered the highest value of 36.2 ng/g egg wet weight in stage VIII. This value, however, declined to a low level in the prehatching stage (IX). The concentration of the free ecdysteroids always predominated over the conjugated ones. The HPLC analysis of free ecdysteroids demonstrated the presence of 20-hydroxyecdysone and ecdysone in the ratio of 2.5. Purified lipovitellin II also contained free and conjugated ecdysteroids. The functional significance of the embryonic ecdysteroids as well as their nature of synthesis and storage within the eggs is discussed in the light of the information available on insect embryogenesis.

Analysis of some morphological and biochemical characteristics of the egg of the predaceous bugMacrolophus caliginosus (Het.: Miridae) during embryogenesis

The predaceous bug,Macrolophus caliginosus Wagner (Heteroptera: Miridae) is a biological control agent used in greenhouses in the French Mediterranean region. The egg of this mirid is embedded in plant tissues and all embryonic development occurs in this environment. In order to define an artificial substrate for egg-laying, exchanges of chemical substances between the egg and the host plant were investigated by morphological and biochemical analyses. Egg wet weight doubled throughout embryonic development, while egg dry weight did not vary. The amino acid content of the egg remained stable during embryogenesis. Only aspartic acid, serine and alanine decreased during the first five days of development. It can be concluded that exchanges mainly involved uptake of water by the egg.

The Effect of Formalin Fixation on Weight of Lizard Eggs

Central to an understanding of life history and reproductive tactics (Stearns, 1976, 1977; Tinkle, 1969; Tinkle et al., 1970) and patterns of parental investment in animals (Smith and Fretwell, 1974; Brockleman, 1975; Congdon et al., 1978, 1981) is the accurate measurement of relevant reproductive characteristics. Offspring size is one such characteristic. A large number of studies have presented various kinds of data on egg size in reptiles as a relative measure of offspring size. Egg size data for reptiles are generally presented as length by width (often then used to calculate volume), egg wet weight, or egg dry weight. In many instances, wet weights of preserved eggs are presented, with no attendant information regarding time of eggs in fixative, and more importantly, correlations between weights of fixed eggs and fresh eggs. In this study, we demonstrate the effect of formalin (10% solution of 39% formaldehyde) fixation on weights of lizard eggs. The only similar comparison we know of is that of Martin (1978) where it was shown that clutch weight/total body weight ratios of lizards were significantly affected by preservation. Small samples of females of three species of lizards, Cnemidophorus septemvittatus, Sceloporus merriami and Urosaurus ornatus, were collected in or near Big Bend National Park, Brewster Co., Texas during early summer of 1981. Lizards were killed, and oviductal eggs were removed, weighed to 0.001 g, and preserved in 10% formalin, a fixative commonly used for reptiles. At three time intervals, 1 wk, 2 wk, and 24 wk, eggs were removed from fixative and reweighed. After 24 wk in formalin, the eggs were freeze dried (-60?C) to constant weight, and dry weights were taken to 0.0001 g. This allowed approximation of water content as well as dry weight. In all cases, means are presented + one standard error of the mean.

Egg quality in rainbow trout: The relation between egg viability, selected aspects of egg composition, and time of stripping

Batches of eggs (1 batch/female) from 17 rainbow trout in their first spawning season were stripped and reared separately, and the percentage which hatched and the percentage which reached the stage of first feeding were determined. The fertilised egg batches were analysed for egg wet weight, egg dry weight, chorion weight and levels in the eggs of free, bound and total lipid, precipitable protein, protein phosphorus, lipid phosphorus, calcium and iron. All determinations were made on single eggs, and six eggs from each batch were analysed for each variable. Results were expressed in absolute terms (as weight of component per egg) and as percentage of egg dry weight. Highly significant variations in all these aspects of egg composition were shown to occur between parent females. However, there was no significant correlation between the percentage of the original number of eggs which hatched and any one aspect of egg composition, except for a weak positive correlation (P<0.05) with the percentage of protein phosphorus in the eggs. Similarly, there was no significant correlation between the percentage of the original number of eggs which reached first feeding and any one aspect of egg composition except for weak positive correlations (P<0.05) with egg wet weight and with both the absolute level and the percentage of protein phosphorus in the egg. There was significant positive correlation (P<0.05) between the percentage of hatched eggs (alevins) surviving to first feeding and each of the following: egg wet weight, egg dry weight and absolute levels in the egg of bound lipid, precipitable protein and protein phosphorus. Egg batches with higher hatching percentage (>50%) differed significantly from those with zero hatching percentage in having (in absolute terms) higher egg weight, chorion weight, protein phosphorus (all P<0.001), egg dry weight, bound lipid and precipitable protein (all P<0.01) and (percentages) higher chorion weight (P<0.05) and protein phosphorus (P<0.001), and lower free and total lipid (both P<0.01) and iron (P<0.05). In a separate experiment to investigate the effects of allowing the eggs to be retained by the female within the abdominal cavity for increasing periods of time after ovulation, eggs were obtained from three females on three or four successive occasions 2–11 days apart. Although the above aspects of egg composition remained almost constant when the eggs were held in the female for up to 18 days after ovulation, the hatching percentage declined sharply within this period, in two females falling from over 90% to near zero. These results together indicate that the time of stripping of the eggs in relation to the date of ovulation is a much more significant determinant of egg quality than any of the chemical and physical aspects of egg composition which were investigated.

Distribution and elimination of a polychlorinated biphenyl during early life stages of rainbow trout ( Salmo gairdneri)

Distribution and elimination of 2,5,2′,5′-tetrachlorobi[ 14C]phenyl (4-CB) were studied during the egg, sac fry, and fry stages of rainbow trout development. Fertilized eggs were exposed to water-borne [ 14C]4-CB for 24 hr and transferred to an incubator containing flowing, 4-CB-free water. The whole egg and its component parts (yolk fluid and chorionic membrane) were analyzed separately for 14C immediately after exposure ( T 0) and 1, 4, 7, 11, 14, and 21 days later. Whole sac fry and its component parts (yolk sac and larva) were analyzed on Days 26, 35, 42, and 49 and whole fry and its component parts (viscera and eviscerated body) on Days 56, 63, 77, 91, and 105. Immediately after exposure ( T 0), 4-CB content of whole eggs was 0.22 ± 0.01 μg/egg (mean ± SE) and 4-CB concentration on a whole egg wet weight basis was 3.72 ± 0.08 ppm. The majority of 4-CB in the eggs was associated with the yolk fluid where it was apparently associated with water soluble lipoproteins and oil globules composed of triglycerides. During the sac fry stage the majority of 4-CB was associated with the yolk sac. However, as the yolk sac was gradually absorbed the 4-CB was transferred to the larva. The time during sac fry development when the greatest absolute amount of 4-CB was present in the larva was at the very end of the sac fry stage. This was also the time when the oil globules in the yolk sac were first consumed by the sac fry before they began feeding on their own. The highest concentration of 4-CB in the larva occurred at the start of the sac fry stage when the eggs hatched. Thereafter larva 4-CB concentration decreased due to larval growth. The most intriguing finding had to do with a change in the rate of whole body elimination of 4-CB during the transition period from the sac fry to fry stage of development. During the egg and first two-thirds of the sac fry stage, 4-CB elimination was slow ( t 1 2 = 231 days ), but during the last one-third of the sac fry stage and throughout the fry stage it was rapid ( t 1 2 = 15 days ). This increased rate of elimination resulted in a loss of nearly all of the 4-CB from the fry. Thus, whole body 4-CB concentration dropped precipitously in the fry and this was due primarily to enhanced 4-CB elimination but also dilution by growth. The mechanism for this rapid whole body elimination of 4-CB in rainbow trout fry is not known but may be related to the low fat content of the fry body.