Daily Egg Production Research Articles

Influence of host density and population structure on egg production in the coccidophagous ladybird, Chilocorus nigritus F. (Coleoptera: Coccinellidae)

1 Studies on aphidophagous coccinellids have indicated that patch quality, and, in particular, the age structure of the prey or the phenological age of the plant, may play an important role in stimulating oviposition behaviour. However, little is known about the egg-laying tactics of coccidophagous species. 2 When restricted to a single, large colony of overlapping generations of their diaspid host Abgrallaspis cyanophylli (Signoret), adult females of the coccidophagous ladybird Chilocorus nigritus F. varied their egg production rate in a cyclic pattern that lasted for approximately 22 days. This information was used to generate hypotheses relating to eliciting cues for oviposition. 3 Two experiments were carried out in the absence of conspecific larvae to assess: (i) whether changes in host density at levels above those needed to sustain egg production in the females affected egg output and (ii) the effect of restricting beetles to various homogeneous prey population structures on daily egg production. 4 Changes in host density caused a significant but transient decline in egg production whereas a heterogeneous prey population elicited significantly higher levels of oviposition than homogeneous ones with similar host densities, irrespective of the growth stage of the prey. 5 Beetles were fed to satiation throughout the experiments but the data obtained suggest that cues for eliciting oviposition operated in a density-dependent fashion. The results of the study are used to discuss the possibility that visual and chemical cues are quantitatively used by ovipositing beetles to assess patch suitability.

Spawning, daily egg production, and spawning stock biomass estimation for common sardine ( Strangomera bentincki) and anchovy ( Engraulis ringens) off central southern Chile in 2002

In this paper, the first daily egg production method (DEPM) parameters were estimated for anchovy and common sardine stocks distributed in the central-south area off Chile (33–40°S). The study area was stratified according to the topography, shape and orientation of the coastal line, and the survey was carried out on the continental shelf during the main spawning peak (August–September, 2002). The bulk of the spawning of both species was successfully covered, which was characterized by a coastal distribution within the first 20 nautical miles, and following the inner zone associated with the 100 m bottom depth. The coastal distribution of the spawning can be related to the oceanographic conditions occurring during the transition from winter to spring (southern Hemisphere), which are characterized by the alternation between northerly and southerly winds. Probably, these factors are interacting to produce enrichment, concentration and retention of egg in coastal zones in the study area. The daily egg production rate ( P 0) was estimated for two geographic strata, and was different in each region. Also, the length frequency and adult reproductive parameters were different between geographic strata, specially the daily spawning fraction. For anchovy, the P 0 was lower in comparison with available estimates for the same species in Peru and in the north area off Chile. Also, the relative fecundity of anchovy was lower, probably because anchovy in the study area have bigger eggs as compared with the anchovy in Northern Chile. The DEPM parameters estimated for common sardine in the investigated area were similar to the range of existing values for the Engraulis genus in other upwelling areas. The stratified spawning stock biomass estimate was 133,031 t (CV = 44%) for anchovy and 706,792 t (CV = 68%) for common sardine. Probably, daily egg production and adult reproductive parameters of both species are highly variables and further research is suggested for improvements future DEPM application for the species.

Interaction of two key pelagic species in the Humboldt Current: euphausiid predation on anchoveta eggs estimated by immunoassays

The euphausiid Euphausia mucronata and anchoveta Engraulis ringens are extremely abundant key components of the pelagic community of the Humboldt Current, and utilize a large fraction of primary production in the euphotic zone. Despite the economic importance of the Peruvian anchoveta, little information exists on the causes of mortality during their early life stages. In this study we: (1) detected and quantified E. mucronata predation on anchoveta eggs in Northern Chile during the winter peak spawning season of 2000 using enzyme-linked immunosorbent assay (ELISA); and (2) estimated the fraction of total natural mortality of anchoveta eggs produced by euphausiid predation. Immunoassay with polyclonal antibodies detected 0.1 µg of anchoveta egg proteins. Potential cross-reactions with proteins of coastal fish eggs were eliminated after the use of electrophoresis, Western blotting and ELISA. Protein detection time in euphausiid guts was 9 h (13°C) and egg protein decay rate was 0.0385 h -1 . Geostatistical analysis identified a large area of egg abundance, and a smaller secondary egg aggregation within the area covered in the regular spawning biomass stock assessment survey in northern Chile (daily egg production method sampling grid). Eighteen percent of total captured euphausiids within the main aggregation of eggs provided positive reactions, indicating anchoveta egg proteins in their guts. Natural mortality rate calculated at the main spawning area was 0.868 d -1 . The potential euphausiid consumption of eggs in this area varied from 3.9 × 10 12 to 4.4 × 10 12 eggs d -1 . Euphausiid predation accounted for 24 to 27% of natural mortality. When added to mortality rate estimates resulting from anchoveta cannibalism in the Hum- boldt Current, our results suggest that half of the daily anchoveta egg production dies daily. Accord- ingly, these estimates challenge classical ideas of trophic webs that do not consider either young developmental stages or interspecific interaction schemes for control of dominant species in pelagic systems.

Is the spawning frequency dependent on female size? Empirical evidence in Sardinops sagax and Engraulis ringens off northern Chile

In this study, we review the relationship between female size and spawning frequency using information from Sardinops sagax and Engraulis ringens, two species which are important for the economy of countries located in the Humboldt Current System. We test the hypothesis that spawning frequency is positively related to female size using information for these two species in northern Chile. The data analyzed were obtained from four different sources: (a) reproductive information obtained from the application of the Daily Egg Production Method (DEPM) in E. ringens between 1992 and 2005; (b) adult reproductive parameters for different species of the genus Engraulis; (c) spawns counts for a brood stock of E. ringens reared in captivity; (c) results from an indirect method based on a gonadosomatic calibrated index developed for S. sagax utilizing data obtained from 1974 to 1996. An analysis of the 11-year DEPM data series for E. ringens suggest that the daily spawning fraction also increases with the average weight of mature anchovy females and that such relationship may also be described using an asymptotic model. A plot of the daily spawning fraction and average female weight data obtained from results of DEPM applications for different Engraulis species from around the world also showed a positive correlation, suggesting that this relationship may be valid for many species, even those located in different habitats. An analysis of the data obtained from the E. ringens brood experiments showed that the number of eggs spawned in the tank increased monthly as female age increased, even though the number of females decreased due to natural mortality. Results in S. sagax females showed that smaller females have shorter spawning periods and a lower spawning fraction; accordingly, bigger females spawned more frequently than smaller ones. The long term estimation (1974–1996) of spawning numbers in relation to S. sagax female size was well described by a sigmoid function.

Effect of an Acidifying Diet Combined with Zeolite and Slight Protein Reduction on Air Emissions from Laying Hens of Different Ages

The objectives of the study were to evaluate the effectiveness of a reduced-emission (RE) diet containing 6.9% of a CaSO(4)-zeolite mixture and slightly reduced CP to 21-, 38-, and 59-wk-old Hy-Line W-36 hens (trials 1, 2, and 3, respectively) on egg production and emissions of NH(3), H(2)S, NO, NO(2), CO(2), CH(4), and non-CH(4) total hydrocarbons as compared with feeding a commercial (CM) diet. At each age, 640 hens were allocated, randomly to 8 environmental chambers for a 3-wk period. On an analyzed basis, the CM diet contained 18.0, 17.0, and 16.2% CP and 0.25, 0.18, and 0.20% S in trials 1, 2, and 3, and the RE diet contained 17.0, 15.5, and 15.6% CP and 0.99, 1.20, and 1.10% S in trials 1, 2, and 3. Diets were formulated to contain similar Ca and P contents. Average daily egg weight (56.3 g), average daily egg production (81%), average daily feed intake (92.4 g), and BW change (23.5 g), across ages, were unaffected by diet (P > 0.05) over the study period. Age effects were observed for all performance variables and NH(3) emissions (P < 0.05). In trials 1, 2, and 3, daily NH(3) emissions from hens fed the RE diets (185.5, 312.2, and 333.5 mg/bird) were less than emissions from hens fed the CM diet (255.1, 560.6, and 616.3 mg/bird; P < 0.01). Daily emissions of H(2)S across trials from hens fed the RE diet were 4.08 mg/bird compared with 1.32 mg/bird from hens fed the CM diet (P < 0.01). Diet (P < 0.05) and age (P < 0.05) affected emissions of CO(2) and CH(4). A diet effect (P < 0.01) on NO emissions was observed. No diet or age effects (P > 0.05) were observed for NO(2) or non-CH(4) total hydrocarbons. Results demonstrated that diet and layer age influence air emissions from poultry operations.

Effects of Lacquer (Rhus verniciflua) Meal Supplementation on Layer Performance

Two experiments were conducted to see the effects of lacquer meal (Rhus verniciflua) on layer performance. In Exp. 1, seventy-two Hy-Line brown layers, 46 wk of age were fed 0, 1.5% and 3.0% lacquer added diets for 6 weeks. Diets contained 2,650 kcal/kg ME and 16.50% CP. In Exp. 2, high-energy diets were fed to 72 Hy-line brown layers of 46 wk age for 6 wk. The diets were: control (3,000 kcal/kg ME and 16.50% CP); Tl and T2 contained 1.5 and 3.0% lacquer respectively, in addition to high energy levels. Each treatment had four replicates with 6 birds each in both the experiments. During Exp.l, there was no effect on average daily feed intake, egg production and feed efficiency, however, egg weight was linearly (p = 0.0128) decreased with the addition of lacquer in diets. The egg quality parameters measured at bi-weekly intervals did not reveal any particular trend. In Exp 2., high-energy diets have decreased the feed intake and egg production in all groups. However, feeding lacquer at 1.5% increased the egg production by 9% than control. The yolk fat content was increased due to treatments showing quadratic trend (p = 0.0683). The liver fat content was decreased by 40-43% than control in lacquer added diets. Except palmitic, oleic and arachidonic acids, some yolk fatty acids showed a linear decreasing trend in lacquer diets. The serum triglycerides and total cholesterol levels were not influenced with lacquer in the diets; however, the serum glucose level was linearly decreased with the addition of lacquer. In conclusion, lacquer meal supplementation significantly affected the performance of layers fed high-energy diets.

Strong material benefits and no longevity costs of multiple mating in an extremely polyandrous leaf beetle, Chrysochus cobaltinus (Coleoptera: Chrysomelidae)

It is well established that females of many species exhibit polyandry. Although such behavior often increases female fitness by augmenting fecundity or enhancing the genetic diversity and vigor of their offspring, it often reduces female longevity. It has been argued that trade-offs between these costs and benefits should limit the degree to which females remate. However, the existence of highly polyandrous species suggests substantial polyandry benefits and/or minimal costs in some systems. Females of the leaf beetle, Chrysochus cobaltinus, are extremely polyandrous, providing an opportunity to examine the factors influencing the evolution of such behaviors. We compared the fecundity and longevity of singly mated females, females that mated multiple times with the same male, and females that mated multiple times with different males. Compared with females in the single mating treatment, females in both multiple mating treatments exhibited a significant reduction in latency to oviposition and, due to an increase in daily egg production, significant increases in lifetime fecundity. This difference diminished as the time since last mating increased. There were no differences in fecundity between the 2 multiple mating treatments, indicating that mate identity does not influence the material benefits of multiple mating. Surprisingly, female longevity did not differ among treatments. The pronounced fecundity benefits that females gain from multiple mating, coupled with a lack of longevity costs, apparently explains the extreme polyandry in this species. In addition, the existence of material fitness benefits via conspecific matings raises the intriguing possibility that in a C. cobaltinus--Chrysochus auratus hybrid zone, heterospecific matings may confer similar benefits to Chrysochus females. Copyright 2006.

Spawning habitat and daily egg production of sardine (Sardina pilchardus) in the eastern Mediterranean

AbstractSpawning habitats of two eastern Mediterranean sardine, Sardina pilchardus (Walbaum, 1792), stocks (coastal waters of central Aegean and Ionian Seas) are characterized from daily egg production method (DEPM) surveys conducted during the peak of the spawning period. The latter occurs earlier in the Aegean Sea (December) than in the less‐productive Ionian Sea (February). Single‐parameter quotient analysis showed that the preferred bottom depth for spawning was 40–90 m in both areas but sardine selected sites of increased zooplankton in the Aegean Sea during December and increased fluorescence in the Ionian Sea during February. Estimates of daily egg production (P) and spawning stock biomass (B) were about four times lower for the Ionian Sea (P = 7.81 eggs m−2, B = 3652 tonnes) than the Aegean Sea (P = 27.52 eggs m−2, B = 16 174 tonnes). We suggest that zooplankton biomass might not be sufficient to support sardine reproduction in the highly oligotrophic Ionian Sea where the very small sardine stock may rely on the late‐winter phytoplankton bloom. Actively selecting sites with increased zooplankton or phytoplankton and feeding plasticity (the well‐known switching from selective particle feeding to non‐selective filter feeding in sardines) are interpreted as adaptations to grow and reproduce optimally at varying prey conditions. Despite differences in temperature and productivity regimes, reproductive performance of sardine in the Ionian Sea was very similar to that in the Aegean Sea during the peak of the spawning period. In comparing adult parameters from DEPM applications to Sardina and Sardinops stocks around the world, a highly significant linear relation emerged between mean batch fecundity (F) and mean weight of mature female (W, g) (F = 0.364W, r2 = 0.98). The latter implies that, during the peak of the spawning period, mean relative batch fecundity (eggs g−1) of sardine is fairly constant in contrasting ecosystems around the world.

The daily egg production method: recent advances, current applications and future challenges

AbstractMore than 120 surveys over 25 years suggest that appropriate use of the daily egg production method (DEPM) provides unbiased but rather imprecise estimates of spawning biomass (coefficient of variation generally above 30%). Knowledge of species reproductive biology and early life history and a survey design adapted to local population dynamics are required to optimize DEPM performance in terms of bias, precision and cost. Clupeoid applications dominate worldwide (mainly for anchovies and sardines) and estimates are often used to tune indirect assessment models or to calibrate other fisheries‐independent methods. The method seems better adapted to the life history of anchovies than of sardines, leading to more precise estimates of anchovy spawning biomass and facilitating extensions of the method to estimate total biomass and numbers at age. The continuous underway fish egg sampler is often used as a secondary sampler in the ichthyoplankton survey of the DEPM to reduce the cost and improve the precision of egg production. Multinomial models were recently developed to analyse egg incubation data and used in a Bayesian procedure for egg ageing and delimitation of daily cohorts. These were incorporated in model‐based estimators to get spatially explicit estimates of egg production, daily fecundity parameters and spawning biomass that can improve the precision of DEPM. Uncertainty in daily fecundity estimation of clupeoids is mainly because of spawning fraction estimation by the post‐ovulatory follicle (POF) method. Exploration of recent histological and molecular techniques for POF characterization and laboratory experiments to test the effect of temperature on POF degradation can help to improve spawning fraction estimation. Available estimates of egg production and mortality, daily fecundity, spawning area and biomass from different populations, species and ecosystems are being used to improve the understanding of clupeoid spawning dynamics, their relation with ecosystem productivity and to build comprehensive population models. Finally, a counter‐intuitive finding of this review is that, although the DEPM is almost exclusively applied to clupeoids, recent evidence indicates that it may be easier and cheaper to use in other teleost families, including demersal species.

Effects of salinity, photoperiod and adult stocking density on egg production and egg hatching success in Acartia tonsa (Calanoida: Copepoda): Optimizing intensive cultures

The interest in large-scale culturing of copepods for marine fish aquaculture is growing, however studies quantifying the optimal conditions for intensive copepod production are generally lacking for most species. In the present study, we examined how large ranges in each of three factors (salinity, photoperiod duration, and culture density) influenced the egg production ( EP) and 48-h egg hatching success ( HS) of Acartia tonsa Dana (Copepoda : Calanoida). The effect of anaerobic storage time (2 to 185 d) at 4 °C on HS of eggs was also quantified. In this species, HS was more strongly impacted by differences in salinity and photoperiod than was EP while the opposite was true for the impact of adult stocking density. In terms of salinity, the lowest and highest mean EP (17 and 40 eggs female − 1 d − 1 ) was observed at 30 and 14 psu, respectively, and HS was estimated to be > 75% for all salinities > 13 psu. The photoperiod duration (used to rear copepods and incubate eggs) had little effect on total daily EP but significantly influenced HS which was 27, 55, 85 and 78% at photoperiods of 8, 12, 16, and 20 h, respectively. Adult stocking density had no effect on HS but the relative number of eggs harvested (# female − 1 ) was highest at 65 ind l − l and lowest at 425 ind l − 1 . For eggs produced using a 12 h photoperiod, HS (%) decreased linearly by 4% every 20 days (i.e., the HS of eggs incubated at 20 psu was predicted to be ∼82% and 47% after one week and six months of storage, respectively). For maximum egg production and 48-h egg hatching success of A. tonsa cultures, results of this study suggest using salinities of 14 to 20 psu, photoperiods between 16 and 20 h, and low (∼50 ind l − 1 ) adult stocking densities.

Life History of Kampimodromus aberrans as a predator of Phytoptus avellanae (Acari: Phytoseiidae, Phytoptidae)

The biology of Kampimodromus aberrans (Oudemans), a predator of the big bud mite, Phytoptus avellanae Nalepa, was studied under laboratory conditions. All experiments were conducted on hazelnut leaf discs in an incubator at 25 +/- 1 degrees C, with 16:8 h L:D, at an average daily relative air humidity of 76%. Observations were made twice daily for the immature stages and daily for the adults to determine developmental time, survival and fecundity. The mean developmental time for females was 6.90 days and for males was 7.10 days, and mean adult longevity for females was 11.67 days. The mean total and daily egg production were 12.67 and 1.85 eggs, respectively. The net reproduction rate (R0) was 7.09 females/female, intrinsic rate of increase (rm) was 0.153 female/female/day and mean generation time (T0) was 12.80 days. The mortality rate of immature stages was 0.66% and the sex ratio was 0.51 female.

Evaluation of Eggshell Quality of Hens Infected with Salmonella enteritidis by Application of Compression

Eggs collected from hens of different ages and that differed in infection status with Salmonella enteritidis were evaluated for the ability to resist cracking following application of maximum compression load from an Instron materials testing machine. Orally infected 24-wk-old hens that were prepeak produced eggs with significantly lower hardness units (HU) of shells compared with a paired control group (P ≤0.01). However, 1 of 3 additional infection trials in hens at peak (29 wk) and older hens postpeak (58 wk) showed an increase in HU in one trial and no difference in the other 2 trials. Thus, Salmonella enteritidis may be able to alter HU in a manner that is influenced by multiple factors, which include the age of the hen and the strain used for infection. Hardness was overall a sensitive physiological barometer of age, because readings correlated positively (all R > 0.50) with hens entering peak production, regardless of infection status. Detection of a very low HU reading (<1.0) was indicative of a hairline crack in the egg, which increased in incidence from 0.01% preinfection to 0.08% postinfection. Two other clinical signs noted postinfection in hens were that i) daily egg production significantly increased in older hens, and ii) emaciation was evident in a few hens that were infected by contact. These results suggest that there may be supportive approaches to achieve reduction of S. enteritidis in table eggs that do not rely on culturing.

Life strategies, energetics and growth characteristics of Calanoides carinatus (Copepoda) in the Angola-Benguela frontal region

Rates of daily egg production, moulting and egg hatching success, as well as total lipid content and composition of Calanoides carinatus, were measured in the region of the southern Angola Curre nt SAC), the Angola-Benguela Front (ABF) and the coastal upwelling area of the northern Benguela Current (NBC) system during February–March 2002. There were distinct differences in the vertical distribution, growth characteristics, lipid content and composition of populations in the SAC/ABF and NBC regions, indicative of different physiological states. Whereas in the NBC, C. carinatus was actively growing in response to elevated chlorophyll a levels associated with coastal upwelling, it comprised deep-living C5 copepodids with very large wax ester reseves (c. 40–50% dry mass) and extremely low metabolism in the SAC/ABF, suggesting diapause. This study provides the first data on lipid composition (lipid classes, fatty acids and alcohols) of this copepod in the region; in particular, the diapausing C5 contained high-levels of long-chain, mono-unsaturated fatty acids (23% of all fatty acids) and alcohols (69% of all fatty alcohols) in addition to trophic markers of diatoms, viz. 16:1(n-7) and 20:5(n-3). Based on total lipidcontent, the maximum survival time of the diapausal component of C. carinatus was estimated to be 149–192 days, whereas active surface-dwelling C5s and females could not survive for more than 10 days without feeding.

Effects of Microbial Phytase Supplementation on Feed Consumption and Egg Production of Laying Hens

In this study, the effects of microbial phytase supplementation in diets were investigated on feed intake, egg production and feed efficiency in laying hens. The experiment was carried out between the July 15 to October 15 . 120 Nick Chick White hens at 210 days of age were divided into four groups of 40 each. th th Each cage contained 5 hens. Treatment groups were fed the basal diet (Control Group) or the basal diet supplemented with 300 U/kg of microbial phytase (Group A) and 600 U/kg of microbial phytase (Group B). Birds in each group were fed a balanced diet ad libitum. Daily feed intake, feed efficiency, egg production and egg weight differed between treatment groups (P<0.01). However initial and final body weights were similar in all groups. It can be concluded that supplementation of microbial phytase to diets improved hen productivity.

Effect of food composition on egg production and hatching success rate of two copepod species (Calanoides carinatus and Rhincalanus nasutus) in the Benguela upwelling system

We have analysed the daily egg production (EPR) and hatching success rates of the calanoid copepods Calanoides carinatus and Rhincalanus nasutus as a function of nano- and microplankton concentration and composition in the northern Benguela upwelling system off Namibia. Food concentration explained 55% (R. nasutus) to 62% (C. carinatus) of the EPR variability. We found no relation between the residuals of the food concentration–EPR regression and the percentage of the different taxonomic components of the nano- and microplankton. Nor was there a relation with the proportion of the diatom Skeletonema costatum that dominated the major blooms or with the number of nano- and microplankton species. We conclude that food quality differences could not be attributed to the relative composition of microplanktonic particles of the different groups (i.e. taxonomic composition).

Life-history traits of the predaceous mite Kampimodromus aberrans (Oudemans) (Acarina: Phytoseiidae) on four different types of food

The developmental time, survival, and fecundity of Kampimodromus aberrans were determined on four different food types, birch pollen ( Betula pendula ) alone; Tetranychus urticae ; T. urticae +birch pollen together and Amphitetranychus viennensis , at 25 ± 1 °C, 65 ± 10% RH, and 16:8 photoperiod under laboratory conditions. Total developmental time of K. aberrans females was 7.9, 10.1, 8.0, and 11.3 days on pollen, T. urticae , pollen + T. urticae , and A. viennensis , respectively. The mortality rate of immature stages of K. aberrans was highest when feeding on spider mites, especially for protonymph stages feeding on T. urticae (% 42 for both sexes). The mortality rate of K. aberrans feeding on pollen was lower than the mortality rate on the other food types. The total and daily egg production rates were the highest on T. urticae and pollen + T. urticae (18.9 and 0.9 eggs; 17.2 and 1.0 eggs, respectively). The total egg production was at its lowest on A. viennensis (5.9 eggs), while the daily egg production was lowest on pollen and A. viennensis (0.6 and 0.7 eggs). K. aberrans feeding on pollen had the highest intrinsic rate of increase, ( r m ), at 0.129 ♀/♀day, followed by 0.108 ♀/♀/day on pollen + T. urticae , while K. aberrans feeding on A. viennensis displayed the lowest at 0.067 ♀/♀/day. On T. urticae , the intrinsic rate of natural increase of K. aberrans was determined as 0.095 ♀/♀/day.

Reproductive parameters of the chub mackerel Scomber japonicus estimated from human chorionic gonadotropin-induced final oocyte maturation and ovulation in captivity

Final oocyte maturation and ovulation of captive chub mackerel Scomber japonicus with fully yolk-accumulated occytes were induced by a single injection of human chorionic gonadotropin. Reproductive parameters, including spawning frequency and batch fecundity, which are required to estimate spawning biomass in pelagic fish by the daily egg production method, were analyzed. Germinal vesicle migration (GVM) occurred at 18–24 h post-injection, and the hydration and ovulation of oocytes were completed at 30 and 36 h post-injection, respectively. The results of the maturation process suggest that fish with GVM-stage ovaries captured in the daytime from the field are capable of spawning on the night following their capture. The oocytes used in the oocyte sizefrequency distribution method for batch fecundity estimates should be at late GVM and more advanced stages. The results of sequential artificial insemination showed that the quality of ovulated eggs held in the ovarian lumen rapidly deteriorated as time progressed after ovulation. This indicates that the fertilization window for the ovulated eggs of chub mackerel lasts only a few hours, and spawning behavior should be performed within a few hours after ovulation in the wild population.

Organic farming production. Effect of age on the productive yield and egg quality of hens of two commercial hybrid lines and two local breeds

Hens of 2 hybrid lines (Hy Line Brown - HLB, Hy Line White - HLW) and 2 local breeds (Robusta maculata – RM and Ermellinata of Rovigo – ER) were reared following the organic production procedure and their egg yield and quality were studied at two different ages (30 and 42 weeks). The experimental period was between 26 and 42 weeks of age, starting in summer and lasting until autumn. Age significantly (P<0.01) affected the hen-day egg production and the daily egg mass of the HLB (84 vs. 94% and 44.5 vs. 59.4 g), of the HLW (81 vs. 89% and 42.4 vs. 54.7 g) and of the RM hens (27 vs. 63% and 12.9 vs. 36.7 g), which was the least precocious. Age did not affect the daily egg production of the ER hens (which was maintained around 58%), although it was observed a slight (P<0.05) increase of the daily egg mass (28.6 vs. 32.1 g). Age increased (P<0.01) the egg weight, yolk colour, yolk percentage and yolk:albumen ratio and decreased the albumen percentage in all groups.

Estimating Baltic sprat (Sprattus sprattus balticus S.) population sizes from egg production

The sprat (Sprattus sprattus balticus S.) population size in the Bornholm Basin, one of the major spawning areas of the species in the Baltic Sea, was estimated with the daily egg production method. Egg abundance, stock structure, sexual and gonadal maturation, spawning frequency and the batch fecundity of sprat throughout the sprat spawning season were simultaneously investigated to obtain an estimate of the population size at spawning time. The results confirmed the population estimate from a hydroacoustic survey, but contrasted spatially down-scaled results from an area dis-aggregated stock assessment model applying fisheries statistics. Conflicting results from both latter methods have previously hampered quantitative studies on recruitment processes of sprat and cod, for example the estimation of predation pressure on cod eggs by sprat. The egg production method did not allow an estimation of the population size of sprat in the entire assessment area larger than the Bornholm Basin, i.e. ICES sub-division 25. This failure is caused by sprat spawning activity outside the Bornholm Basin, not covered by the standard egg surveys and has consequences for the general applicability of available egg abundance time series to retrospectively estimate sprat stock development.

Aspectos biológicos de Chrysoperla externa (Hagen, 1861) (Neuroptera: Chrysopidae) alimentada com Bemisia tabaci (Gennadius, 1889) biótipo B (Hemiptera: Aleyrodidae) criada em três hospedeiros

Estudaram-se alguns aspectos biológicos de adultos de Chrysoperla externa (Hagen) oriundos de larvas alimentadas com ninfas da mosca-branca Bemisia tabaci (Gennadius) biótipo B, criadas em folhas de pepino (Cucumis sativus) var. caipira, couve (Brassica oleraceae) var. acephala e na planta invasora leiteiro (Euphorbia heterophylla). Discos foliares dos hospedeiros contendo ninfas de terceiro e quarto estádios da mosca-branca foram acondicionados em placas de Petri contendo ágar-água a 1%. Em cada placa foi colocada uma larva de C. externa recém-eclodida, onde permaneceram até a emergência dos adultos. Foram avaliados o peso logo após a emergência, os períodos de pré-oviposição, oviposição, efetivo de oviposição, pós-oviposição, número total de ovos produzidos por fêmea e longevidade. Avaliaram-se, também, o período embrionário e a viabilidade dos ovos, coletando-se, uma vez por semana, uma amostra de 10% do total de ovos produzidos no dia, ao longo de todo o período reprodutivo. O peso de machos e fêmeas não diferiu significativamente em função do hospedeiro da presa, sendo em média de 4,7 mg. De maneira geral, adultos de C. externa oriundos de larvas alimentadas com ninfas de B. tabaci biótipo B criadas em leiteiro apresentaram performance inferior em relação àqueles oriundos do pepino e da couve. O período de oviposição foi, em média, de 49,5 dias para o pepino e a couve, e de 31,6 dias para o leiteiro. A produção de ovos foi reduzida em aproximadamente 50% em leiteiro, sendo de 293,8 ovos; no pepino e couve, a média foi de 591,3 ovos. Ninfas de B. tabaci biótipo B criadas em leiteiro causaram uma redução da viabilidade dos ovos de C. externa, que foi 62,8% e 57,7% inferior ao verificado para o pepino e a couve, respectivamente.