Individual Egg Production Research Articles

Maternal source of variability in the embryo development of an annual killifish.

Organisms inhabiting unpredictable environments often evolve diversified reproductive bet-hedging strategies, expressed as production of multiple offspring phenotypes, thereby avoiding complete reproductive failure. To cope with unpredictable rainfall, African annual killifish from temporary savannah pools lay drought-resistant eggs that vary widely in the duration of embryo development. We examined the sources of variability in the duration of individual embryo development, egg production and fertilization rate in Nothobranchius furzeri. Using a quantitative genetics approach (North Carolina type II design), we found support for maternal effects rather than polyandrous mating as the primary source of the variability in the duration of embryo development. The number of previously laid eggs appeared to serve as an internal physiological cue initiating a shift from rapid-to-slow embryo developmental mode. In annual killifish, extensive phenotypic variability in progeny traits is adaptive, as the conditions experienced by parents have limited relevance to the offspring generation. In contrast to genetic control, with high phenotypic expression and heritability, maternal control of traits under natural selection prevents standing genetic diversity from potentially detrimental effects of selection in fluctuating environments.

Growth, egg production and hatching success of Acartia tonsa cultured at high densities

Acartia tonsa is a calanoid copepod with high potential as live feed for marine aquaculture. However, its usage remains limited at an industrial scale, with cost effective production being conditional on successful culture at high density. The present study took an integrated approach to provide further insight on the effects of A. tonsa stocking density on copepod growth and adult reproduction, specifically egg production and egg hatching success. The effect of stocking density was studied by following the growth and survival of A. tonsa copepods, from egg hatching to maturity, on cultures initially stocked with 250, 400, 1000, 3000 and 6000copepods l−1. Additionally, the effects of high-density rearing, of adults kept at 100, 250, 500 and 2500copepods l−1, on egg production and hatching success were also evaluated over a 5-day period.Higher stocking densities were shown to have no unfavourable effect on copepod growth, though mortality significantly increased with density, from ≤2.5%d−1 at densities of ≤1000copepodsl−1 to 3.5–4.0%d−1 at 3000–6000copepodsl−1. Individual egg production decreased with increasing stocking densities, from 28eggsfemale−1d−1 at 100copepodsl−1 to 7eggsfemale−1d−1 at 2500copepodsl−1. However, total yield still increased with stocking density, with the cumulative egg production at 2500copepodsl−1 being 4 times the production at lower densities (from 100 to 500copepodsl−1). Though adult rearing density had no effect on 96-h hatching rate (60 to 69%), a density-dependent late hatching was observed on eggs produced by adults grown in dense cultures (500–2500copepodsl−1), with 48-h hatching success significantly decreasing with increasing densities (from 37% to 1%).In spite of the negative effect of stocking density on survival during growth and egg production, the magnitude of these effects does not compromise the use of high density cultures. Future research should focus on the improvement of production systems, as the ability to rear calanoid copepod species at large scale would present a major advancement in larviculture of marine fish species. Supporting statementThe present research focused on the effects of A. tonsa stocking density on copepod growth and adult reproduction, specifically egg production and egg hatching success. This is the first study on A. tonsa high-density culture from copepod growth to egg production and hatching. It further provides new insight on the viability of using high-density cultures for egg production and its impact on hatching success, essential for the commercial production of this species

Environmental effects on sprat (Sprattus sprattus) physiology and growth at the distribution frontier: A bioenergetic modelling approach

Sprat, Sprattus sprattus, is a small pelagic fish species with a wide distribution along the European continental shelf, the Mediterranean Sea, the Black Sea and the Baltic Sea. The Baltic Sea is the coldest area of the species distribution range. Even here, sprat is still numerous and holds a key role in the ecosystem. However, the population is sensitive to small changes in environmental conditions. In this paper, we set up a bioenergetic model of Baltic sprat and evaluate how variability and seasonal changes in the physical environment affects the physiology and growth of individual sprat. The model is dynamic and seasonally resolved. It is parameterised based on sprat from the Bornholm Basin. Our model results suggest that the optimal temperature for sprat growth is 17.5°C, which is only observed in the Central Baltic Sea in the top water layer during a short period in summer. During 4½ winter months individual sprat do not grow and utilize stored energy from the previous growth season. We analysed the maximum attainable individual body size as a function of temperature. The model predicted reduced maximum body sizes with increasing temperature. The model can be used for studying climate change scenarios on individual growth, egg production and condition of Baltic sprat.

Integrating fish size, condition, and population demography in the estimation of Atlantic sardine annual fecundity

Spatial and temporal variability in reproductive parameters was studied in combination with population demography to estimate sardine (Sardina pilchardus) population annual fecundity, as an indicator of its reproductive potential. Samples collected from commercial landings were used to determine the monthly proportion of active females and the duration of the spawning season, while data obtained during the 2002, 2005, and 2008 Daily Egg Production Method surveys were used to analyze the relationship between reproductive parameters (batch fecundity, spawning fraction) and individual biological characteristics (length, gutted weight, condition) for the west and south coasts of Portugal by generalized linear models. Population abundances and biological characteristics obtained per length class during acoustic surveys were subsequently used to integrate individual egg production to population demography. At the individual level, results indicated that the duration of the reproductive season was size-dependent, being shorter for smaller sardines. Batch fecundity was positively related to body size and differed significantly between the years and areas studied, with higher values on the west coast and an increasing trend towards the 2007/2008 spawning season. Mean values of spawning fraction varied significantly with space and time but the poor explanatory relationship obtained by the modelling of the spawning fraction against the individual biological characteristics did not allow the clarification of the factors affecting sardine spawning activity. At the population level, the differences obtained in egg production were found to be related to changes in population abundances as well as to the demographic structure, as larger females contributed proportionally more to the population annual fecundity. These results are in accordance with numerous recent studies indicating that the population reproductive potential may not always be proportional to the spawning biomass.

Broodiness, egg production, and correlations between broody traits in an indigenous chicken breed

The influence of broodiness on egg production was evaluated, and correlations between the age of the first broody cycle (AFB), duration of first broody cycle, and interval between the end of the first broody cycle and the re-laying of eggs were calculated in Chinese Qingyuan (Q line) chicken. In addition, age at first egg and individual egg production were recorded. From a single hatch, hens were randomly divided into 2 groups, group A (n=576) and group B (n=576). Group A hens were allowed to go through the entire broody cycle, whereas group B hens were treated so as to interrupt the cycle. Mean incidence of broodiness was approximately 15%, with the average AFB at approximately 40 wk (i.e., about 20 wk after the onset of lay). Nonbroody hens produced more eggs than broody and treated hens. However, a higher laying rate during the nonbroody period partially compensated the egg loss from broodiness. Negative correlations (P<0.01) were found between AFB and duration of first broody cycle or interval between the end of the first broody cycle and the re-laying of eggs, indicating that the age of the first broody cycle can be regarded as a phenotypic marker for intensity of broodiness in hens.

The Restricted Ovulator Chicken: A Unique Animal Model for Investigating the Etiology of Ovarian Cancer

The main goal of this study was to compare the incidence of ovarian cancer (OC) in 2 genetically different lines of hens--one that generally fails to lay eggs (the mutant "restricted ovulator" [RO] strain) and the other consisting of the wild-type (WT) siblings of the mutant RO hens. Individual egg production data were obtained over a 972-day period for 31 RO hens and 33 WT hens. At 38 months of age, hens were killed, and their abdominal cavities were examined for any gross evidence of tumors. Samples of ovarian tissue were processed and assessed for histopathology and protein expression of ovalbumin. Plasma estradiol concentrations were also determined. Only 1 (3%) of the 31 RO hens was diagnosed with OC as compared with 9 (27%) of the 33 WT hens (P G 0.05). Wild-type hens laid more eggs than did RO hens during the 31-month collection period (average of 422 vs 28, respectively; P < 0.05). Although there was no difference in overall rate of ovulation between hens with and without OC, WT hens diagnosed with OC laid a greater percentage of their total number of eggs in the first year of production. Plasma estradiol concentrations were higher (P < 0.01) in RO versus WT hens. The results of this study strongly suggest that the number of ovulatory events is directly related to the incidence of OC in chickens. Clearly, other factors modify the risk of OC because there was no difference in ovulation rate between WT hens with and without OC. The mutant RO hen represents a valuable animal model for studying the etiology of OC.

Egg production of Calanus finmarchicus—A basin-scale study

Egg production of Calanus finmarchicus was studied during joint basin-scale surveys in April-June 2003 in the Norwegian Sea. Surveys covered the whole Norwegian Sea and were conducted from Norwegian, Icelandic and Faroese research vessels. Stations were classified as being in pre-bloom, bloom or post-bloom phase according to levels of chlorophyll a and nitrate. Individual egg production rates and population egg production rates were calculated and compared between areas. Both individual egg production rates (eggs female -1 day -1 ) and population egg production rates (eggs m -2 day -1 ) were significantly higher in bloom areas compared with pre-bloom and post-bloom areas. However, when integrated over an estimated duration of the three phases, the time-integrated egg production (eggs m -2 ) in most years was highest in the pre-bloom phase, and this was explained by the longer duration of this phase compared with the two other phases.

Changes in numbers of large ovarian follicles, plasma luteinizing hormone and estradiol-17β concentrations and egg production figures in farmed ostriches throughout the year

In this study we described and analysed changes in the numbers of large ovarian follicles (diameter 6.1–9.0 cm) and in the plasma concentrations of luteinizing hormone (LH) and estradiol-17β (E 2β) in relation to individual egg production figures of farmed ostriches ( Struthio camelus spp.) throughout one year. Ultrasound scanning and blood sampling for plasma hormone analysis were performed in 9 hens on a monthly basis during the breeding season and in two periods of the non-breeding season. Our data demonstrated that: (1) large follicles were detected and LH concentrations were elevated already 1 month before first ovipositions of the egg production season took place; (2) E 2β concentrations increased as soon as the egg production season started; (3) numbers of large follicles, LH and E 2β concentrations were elevated during the entire egg production season; and that (4) numbers of large follicles, LH and E 2β concentrations decreased simultaneous with or following the last ovipositions of the egg production season. By comparing these parameters during the egg production season with their pre-and post-seasonal values, significant differences were found in the numbers of large follicles and E 2β concentrations between the pre-seasonal, seasonal and post-seasonal period; while LH concentrations were significantly different between the seasonal and post-seasonal period. In conclusion, our data demonstrate that changes in numbers of large follicles and in concentrations of LH and E 2β closely parallel individual egg production figures and provide some new cues that egg production in ostriches is confined to a marked reproductive season. Moreover, our data provide indications that mechanism, initiating, maintaining and terminating the egg production season in farmed breeding ostriches are quite similar to those already known for other seasonal breeding bird species.

Role of essential fatty acids on the reproductive success of the copepod Temora longicornis in the North Sea

This field study focused on the transfer of dietary fatty acids (FAs) into the eggs of Temora longicornis and assessed their potential for limiting egg production and egg viability. In situ egg production rates (EPRs), hatching success and FA profiles of females, as well as eggs, were deter- mined and compared to food indicators, i.e. particulate organic carbon, particulate organic nitrogen and FAs of size-fractionated seston samples. Individual egg production ranged from 14 to 28 eggs female -1 d -1 , corresponding to weight-specific egg production rates (sEPRs) from 0.18 to 0.35. Based on trophic marker FAs, T. longicornis most likely fed non-selectively. FA contents of eggs ranged from 2.6 to 4.3 ng egg -1 and correlated significantly with the FA content in seston (size class: 1 to 30 µm). Strong similarities in FA profiles of eggs and seston, as well as correlations of absolute FA levels, indicated only minor maternal regulation of egg composition. The significant increase in EPRs with an increasing diatom food supply, as indicated by correlation with 16:1(n-7) levels in seston and eggs, strongly compensated for the tendency to produce less viable eggs on a diatom-dominated diet. Egg viability was overall very high (77 to 94%) at all our stations and did not relate to essential FA levels in the eggs, indicating that lipids were transferred in sufficient quantities. Thus, food quantity rather than quality determined the reproductive success of T. longicornis during our study. Stoichio- metric comparisons between seston and egg composition suggested that nitrogen-containing com- pounds had a higher potential for limiting egg production during our study than essential FAs.

HOW TRANSIENT PATCHES AFFECT POPULATION DYNAMICS: THE CASE OF HYPOXIA AND BLUE CRABS

Transient low-oxygen patches may have important consequences for the population dynamics of estuarine species. We investigated whether these transient hypoxic patches altered population dynamics of the commercially important blue crab (Callinectes sapidus) and assessed two alternative hypotheses for the causal mechanism. One hypothesis is that temporary reductions in habitat due to hypoxia increase cannibalism. The second hypothesis is that crab population dynamics result from food limitation caused by hypoxia- induced mortality of the benthos. We developed a spatially explicit individual-based model of blue crabs in a hierarchical framework to connect the autoecology of crabs with the spatial and temporal dynamics of their physical and biological environments. Three primary scenarios were run to examine the interactive effects of (1) hypoxic extent vs. static and transient patches, (2) hypoxic extent vs. prey abundance, and (3) hypoxic extent vs. cannibalism potential. Static patches resulted in populations limited by egg production and recruitment whereas transient patches led to populations limited by the effects of cannibalism and patch interactions. Crab survivorship was greatest for simulations with the largest hypoxic patches which also had the lowest prey abundance and lowest crab densities. In these simulations, nearly all crab mortality was accounted for by aggression, not starvation. In addition, increased prey abundance had little influence on crab abundance and dynamics, and massive reductions in prey abundance (.50%) were necessary to decrease crab abundance, survival, and egg production. Our analyses suggest that cannibalism coupled with decreased egg production determined key aspects of crab demography. Specifically, decreased cannibalism potential resulted in a food-limited crab population with long development times and high adult crab densities whereas increased cannibalism potential led to low adult crab densities with higher individual egg production rates. Our analyses identified several key knowledge gaps, including the nature of crab-crab cannibalism and the role of refuges from predation. Several experiments are suggested to test model predictions and to improve understanding of ecosystem-population linkages for this estuarine species.

Ultrasonography of the female reproductive organs in farmed ostriches (Struthio camelus spp.).

The main objective of this study was to determine whether transcutaneous ultrasonography could be used as a diagnostic tool to monitor the reproductive organs of female breeding ostriches. An additional aim was to investigate whether the use of this technique could facilitate prediction of the start or end of the egg production season. A technique for on-farm ultrasound scanning is described and examples of ultrasonographic images of different ovarian structures, developing ova and eggs within the genital tract are presented. These data were obtained by scanning mature female breeding ostriches (n=8). In vivo scanning took place a day prior to slaughter, and immediately after slaughter the reproductive organs were scanned in vitro in a water bath. By comparing ultrasonographic images with post mortem ovarian morphology, it appeared that the following morphological structures can be identified using ultrasonography: ovarian follicles of different sizes (diameter (phi) 1-9 cm), atretic follicles, post-ovulatory follicles (POFs), ova at different stages of development and eggs within the genital tract. Of the number of follicles counted during post mortem investigation, 58% (95% confidence interval 0.41-0.79) had been detected during previous in vivo examination. In the second part of our study, ultrasonographic scans were made at weekly intervals in two farmed female ostriches (n=2) during the breeding season in order to determine the predictive value of the technique. By comparing the images of ovarian activity with individual egg production of these hens, preliminary evidence was obtained that scanning might be of value in predicting egg production, especially at the start and the end of the breeding season. It is concluded that transcutaneous ultrasound scanning in mature female breeding ostriches is an easy, noninvasive technique for the monitoring of ovarian (in)activity, for visualization of different functional ovarian structures, for following the development of individual ova and for visualization of an egg with calciferous shell within the oviduct, and that this technique will be a valuable tool in future research on reproductive physiology and pathology, and the development of more advanced reproductive technologies, such as artificial insemination.

Large spatial variability in lifetime egg production in an intertidal Baltic tellin (Macoma balthica) population

The extent to which it pays settling larvae of marine benthic organisms to actively select the habitat where they will spend the rest of their life can only be fully appreciated if the fitness consequences of such habitat selection processes are known. We estimated the lifetime egg production of the tellinid bivalve Macoma balthica at 11 sites over a tidal gradient in the western Wadden Sea, using a 30-year data series. The difference in individual lifetime egg production between the best sites in the lower tidal zone and the poorest sites on the high tidal flats was about a factor 10. The differences in lifetime egg production were related to differences in growth and, more importantly, survival. We argue that the large observed differences in reproductive output do not necessarily imply a lack of active habitat selection. As most animals start their last migration before final settlement from the high tidal flats, the choice may be one between a long and risky migration with a low chance of reaching the good habitat versus a more certain but poor existence on the high tidal flats.

Associations Between Egg Production and Clutch Length in Four Selected Lines of Chickens

The use of partial records to measure egg production of pedigree breeders has numerous advantages including reduced labor and generation interval. Maintaining egg production in an era where emphasis in breeding programs involves yield and feed conversion presents a challenge to primary breeders. Because breeders obtain individual egg production records, interest in the possibility of using the association of various measures of clutch length with intensity of egg production has been renewed. The correlation of maximum clutch length (prime sequence) throughout lay and during the first 10, 15, and 30 d of lay with percentage hen-day ovulations and normal eggs in four lines (two White Leghorn and two White Plymouth Rock) of chickens during each of 2 yr was measured. Although the rankings of the lines were generally consistent both years for all traits measured, correlations among the sequence lengths with percentage henday ovulations and normal eggs were line specific. Thus, poultry breeders would have to determine which of these measures is most appropriate for inclusion with other measures of egg production for each of their specific lines.

A Model for Individual Egg Production in Chickens

Our primary objective was to improve on an existing model for the individual weekly egg production curve by modeling the curve as a sum of logistic functions: one for the increasing phase of production and a sum for the decreasing phases. To illustrate the model, we used four data sets from two pairs of individuals.For these data, the model consisted of an increasing phase and a single decreasing phase of production: yt=m k1(1-e-t1+e-t)-m(k1-k2)(1+e-t1+e-(t-c2))where yt is egg production at week t, m is maximum production during a specific time interval, k1 is proportion of maximum production for the increasing phase, k2 is proportion of maximum production for the decreasing phase, and c2 is point of inflection from the upper level of the increasing phase to the lower level of the decreasing phase; thus, c2 is a measure of persistency of egg production.For one pair of individuals, production was about 88% of maximum (k1) for the increasing phase and about 76% of maximum (k2) for the decreasing phase. For the other pair, production was about 91% of maximum (k1) for the increasing phase and about 75% of maximum (k2) for the decreasing phase. Persistency (c2) was about 25 wk for one pair and about 28 wk for the other. Predicted total 52-wk production was within one or two eggs of actual production.The secondary objective was to improve estimation of model parameters by summarizing egg production data by 1-wk, 2-wk, or 4-wk intervals and by using cumulative egg production instead of weekly production. For weekly production, estimates of parameters changed only slightly, as intervals increased from 1 wk to 2 wk or to 4 wk. Predicted total 52-wk production, however, decreased up to five eggs as interval increased from 1 wk to 4 wk.For cumulative egg production by time t, Yt, the model was Yt=7k1[2ln(1+et3)-t]-7(k1-k2)[(1+e-22)Ln(ec2+et1+ecc)-te-c2].For cumulative production, estimates of parameters changed only slightly, if at all, as intervals increased from 1 wk to 4 wk. Predicted 52-wk production, however, approached the actual number as interval increased from 1 wk to 4 wk.Prediction of annual (52-wk) egg production based on part-record production for only the first 22 wk might lead to over-prediction because persistency of production lasted longer than the part record. Genetic gain from selection to improve annual production, therefore, might be increased if selection accounted for persistency of production and for the multiphasic shape of the individual egg production curve, and if data were summarized by 4-wk intervals and cumulated.

Interactions between the Steinernema feltiae–Xenorhabdus bovienii Insect Pathogen Complex and the Root-Knot Nematode Meloidogyne incognita

The interactions between a plant-parasitic nematode, Meloidogyne incognita, and an entomopathogenic nematode, Steinernema feltiae, and its associated symbiotic bacterium, Xenorhabdus bovienii, are described. Our objective was to determine the manner in which the presence of the S. feltiae–X. bovienii nematode–bacterium complex affected infectivity and reproduction of M. incognita in tomato roots (cv. Rutgers). Tests demonstrated that a common application rate of S. feltiae for insect control, 2.5 billion/ha (scaled to our laboratory and greenhouse tests), significantly decreased M. incognita galling, egg production, and egg hatch rate. Two time course experiments were conducted against M. incognita with rates of S. feltiae that corresponded to the effective concentrations. In the first time course experiment, M. incognita and S. feltiae were applied the same day to tomato seedlings in sand. Twelve plants were assessed destructively each week for 6 weeks after inoculation with the two nematode species. Neither M. incognita penetration rate nor developmental rate was affected by S. feltiae application. Egg production per plant and egg hatch rate were significantly reduced in the treated plants. However, the number of eggs per egg mass in treatment plants was not different from that in control plants. The average number of galls per plant 6 weeks after the initial inoculation was lower in the treated plants than in the control plants. In the second time course experiment, the same rate of S. feltiae was applied to sand in which plants already infected with M. incognita had been transplanted. Development of nematodes inside the root was not affected by S. feltiae in the sand. Galling 6 weeks after the application was again less in the treatment than in the control plants. The presence of the S. feltiae–X. bovienii complex at a density that reflects the recommended field application rate had suppressive effects on M. incognita in these laboratory trials. Our data show that S. feltiae applications decrease M. incognita galling, egg production per plant, and egg hatch but not individual female egg production.

Reciprocal crosses between Alabio and Mojosari ducks : early egg production

alternative to increasing productivity and production efficiency. Crossbreeding has been used widely for increasing productivity, and in this experiment Alabio and Mojosari ducks were crossed reciprocally in order to evaluate their egg production and egg quality, when compared to their parental breeds. Four genotypes AA, AM, MA and MM were compared and each consisted of 50 layer ducks. Each animal was kept in individual cage, and individual egg production and egg quality were recorded. They were given layer feed containing 20% crude protein and 3000 kcal/kg metabolisable energy. Results showed that the crossbred ducks (AM and MA) laid eggs earlier than their parental breeds (AA and MM), and MA laid earlier than AM. The weight of first eggs of the crossbreeds did not differ significantly, AM was the same as MM and MA the same as AA. For the body weight at first lay, MA and AM weighed in between their parental breeds, AA was the heaviest and then followed by MA, AM and MM. For the 3-month egg production, MA ducks laid significantly more egg than the other 3 genotypes, and this is related to the age of first lay being the earliest. In terms of egg quality such as egg weight, yolk color, weight and thickness of shell, weight of the white and HU value, the crossbred ducks showed quality in between AA and MM. The AM ducks tended to be closer to MM and MA closer to AA, and this shows a strong influence of maternal effects. The average level of heterosis for weight of first egg is 2.41% and for 3-month egg production is 2.1%, but for MA cross the heterosis level is 11.69% for egg production. The overall results showed that crossbreeds between Alabio and Mojosari have the potential in improving production traits in the effort to increase productivity and production efficiency. Key words : Duck, crossbred, production egg

Effect of dietary protein level on the reproductive performance of Nile tilapia, Oreochromis niloticus (L.)

The effects of five dietary protein levels (25%, 30%, 35%, 40% and 45%) on the individual spawning frequency and the egg production of 135 tagged female Nile tilapia, Oreochromis niloticus (L.), were studied from 8 May to 19 November 1996 in outdoor concrete tanks. Virtually identical spawning patterns were found in all treatments, but there was a great deal of variation in the frequency of spawning and egg production. Overall, individual spawning frequency varied from one to 14 and individual egg production from 31 to 2828 eggs per spawning. The average number of spawnings and average number of eggs per spawning for fish receiving dietary protein levels of 25%, 30%, 35%, 40% and 45% were 8.0 ±1.6, 8.4 ± 2.2, 8.5 ± 2.7, 8.4 ± 2.5 and 9.4 ± 2.1 spawnings, and 1167 ± 305, 1082 ± 410, 1288 ± 324, 1145 ± 389 and 1328 ± 311 eggs per spawning, respectively. Fish receiving 45% dietary protein spawned more frequently than fish receiving 25% dietary protein. The total number of eggs produced per female was significantly higher for females fed 45% protein feed than females receiving 25% and 30% protein feeds. No definite trend was found in the number of eggs produced per spawning and the number of eggs produced per gram in females fed at different protein levels. Based on weekly checking, the time interval between spawnings varied from 7 to 77 days, and mean spawning intervals ranged from 15.8 to 17.1 days. Sixty per cent of females spawned after an interval 14 days, 15% after 21 days, 13.6% after 7 days, 7.2% after 28 days, 1.8% after 35 days and 1.0% after 42 days, and the time interval was 49-77 days for the rest of the females (1.5%). In all treatments, maximum spawning activity was recorded from May to August, and thereafter, it gradually decreased and no spawning females were found in November.

Effects of age at photostimulation on reproductive efficiency and carcass characteristics. 1. Broiler breeder hens

The effect of age at photostimulation on carcass composition at photostimulation and at sexual maturity as well as its effect on subsequent reproductive performance in broiler breeders was investigated. A total of 600 broiler breeder pullets were reared in light-tight facilities. Skip-a-day feeding was used after 2 wk of age to limit body weight to levels suggested by the breeder. Limited daily feeding was initiated at the time of caging (time of photostimulation). The photoperiods used during rearing and lay were 8L:16D and 14L:10D, respectively. Forty birds were selected for study and moved to laying cages and photostimulated at 120, 130, 140, 150 or 160 d of age. Individual egg production records were kept until 60 wk of age. Twenty additional birds were killed for study of carcass composition and reproductive organ, morphology at the time of photostimulation and 20 others were killed at sexual maturity (first oviposition).As age at photostimulation increased, body weight and percent carcass lipid content increased while percent water and ash content decreased. No significant differences were found among treatment groups at photostimulation for carcass protein content. No significant differences were found in any carcass composition parameter at sexual maturity. All groups showed an increase in lipid content from photostimulation to sexual maturity, with the 120 d treatment group showing the largest increase. As age at photostimulation increased, the time from photostimulation to sexual maturity decreased. Total egg production, first egg weight, total egg mass produced, average fertility, hatchability and hatch of fertile did not differ significantly among treatment groups. Chick production was significantly higher in the 140-, 150- and 160-d treatment groups compared with the 120- and 130-d treatment groups. One explanation for the high rate of egg production seen in birds photostimulated at the older ages was that these birds reached sexual maturity with less between-bird variation. To take advantage of this improved flock uniformity, delaying photostimulation to 140 d of age or later is recommended. Key words: Chicken, broiler breeder, sexual maturity, egg production, hatchability, carcass composition

Comparative spring distribution of zooplankton in three macrotidal European estuaries

The zooplankton of three european estuaries (Ems, Gironde and Westerschelde) was investigated during spring 1992 by means of samples taken along the salinity gradient. The three estuaries are comparable in terms of total area, flushing time and salinity gradient but differ by their level of eutrophication (highest in the Westerschelde), suspended matter concentration (highest in the Gironde) and potential phytoplankton production (highest in the Ems). Copepods and meroplankton dominated the zooplankton in the three estuaries. The dominant copepod species were Eurytemora affinis and Acartia bifilosa. The distribution of E. affinis along the salinity gradient differed between the estuaries. Peaks of abundance were observed at 0 PSU in the Gironde, 6 PSU in the Ems and 9 PSU in the Westerschelde. The downstream shift of the population in the Westerschelde was likely due to anoxic conditions occurring in the oligohaline zone. In the Gironde the downstream distribution of E. affinis was limited by the very high suspended matter concentration found in the maximum turbidity zone. Whatever the estuary, the parameters of the population of E. affinis and maximum abundance values were similar. However, the influence of the better quality of the available food was suggested in the Ems where individual dry weights and egg production were higher than in the two other estuaries. The influence of a good quality of food in the Ems was confirmed by the development of a large population of Acartia bifilosa (as abundant as E. affinis) and highest values of adult individual weights.

Size specific demography of three species of Anastrepha fruit flies

Individuals of three Anastrepha species: A. obliqua, A. ludens, and A. serpentina (Diptera: Tephritidae), were sorted according to pupal weight in cohorts of large and small flies. Demographic parameters and reproductive patterns and heterogeneity were determined for each cohort. Large flies of the three species presented greater expectation of life and gross fecundity rates. A. ludens was the species with the longest life span (expectation of life of large adults was 110 days) and the greatest gross fecundity rates (1597 eggs/female for the large flies). While, A. obliqua had the shortest mean age of reproduction (33 days), and the greatest daily egg production (14 eggs/female/day). Net fecundity was similar in these two. A. serpentina had lower fecundity rates. Reproductive information for each size and each species include: age-by-parity relations, fraction of sexually mature life in which females lay eggs, and frequency distribution of individual egg production. Results demonstrate that even under constant laboratory conditions and using standard artificial hosts, there is a great deal of life history variation among these Anastrepha species and among other tephritid fruit flies.