Mean Female Length Research Articles

Reproductive biology of Macrobrachium surinamicum (Decapoda: Palaemonidae) in the Amazon River mouth

Macrobrachium surinamicum is an indigenous prawn distributed from the lower Amazon and Tocantins river basins to Venezuela in the Orinoco Delta region. It is common bycatch fauna of Macrobrachium amazonicum artisan fishing in the states of Pará and Amapá. The aim of this study was to investigate aspects on reproductive biology (reproductive period, size of sexual maturity population, fecundity, reproductive output and recruitment) of M. surinamicum from four important areas to artisanal prawn fishing located at the Amazon River mouth (Amapá and Pará). The specimens were captured using 20 handcrafted traps called "matapi". A number of 675 prawns were captured, 258 males, 409 females and eight juveniles, resulting in 1:1.6 (Male: Female) sex ratio. The reproductive peak period occurred from March to July, coinciding with the higher rainfall period. The juvenile prawn occurred only in May and July. Total length of egg-bearing females ranged from 12.12 to 38.30 mm, with mean female length at first maturity (L50) of 23.7 mm. Fecundity increased with prawn size and varied between 174 and 1780 eggs per female. Mean egg volume increased gradually from 0.031 (Stage I) to 0.060 mm³ (Stage III) during embryogenesis. Macrobrachium surinamicum depends on brackish water to complete the larval development. Irrespective of female size, reproductive output of M. surinamicum varied between 4.3 % and 35.5 % of their body weight for egg production. The knowledge of the reproductive biology reported in the present study is an important tool to define strategies to preserve M. surinamicum in Amazon River mouth.

Environmental factors affecting recruitment of northern shrimp Pandalus borealis in West Greenland waters

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 469:297-306 (2012) - DOI: https://doi.org/10.3354/meps09794 Environmental factors affecting recruitment of northern shrimp Pandalus borealis in West Greenland waters Kai Wieland1,*, Helle Siegstad2 1Technical University of Denmark, Institute of Aquatic Resources (DTU Aqua), 9850 Hirtshals, Denmark 2Greenland Institute of Natural Resources (GINR), 3900 Nuuk, Greenland *Email: kw@aqua.dtu.dk ABSTRACT: Survey estimates of northern shrimp Pandalus borealis biomass in West Greenland waters increased from about 178000 t in 1998 to about 598000 t in 2003. The increase in stock size was preceded by several consecutive years in which recruitment was substantially above average. Recruitment has been poor since then despite record high levels of female stock biomass. Ricker-type stock-recruitment functions did not indicate that the variability in recruitment was related to female biomass. Multiple regression analysis revealed that mean female length, ambient bottom temperature and biomass of Greenland halibut Reinhardtius hippoglossoides had the most important effect on the variations of the ‘recruit per female biomass’ time series for the years 1993 to 2011. Variables which did not contribute significantly to the model included biomass of Atlantic cod Gadus morhua. This can be explained by the low stock size of Atlantic cod throughout the major part of the study period. The final model explained 83% of the variation in the recruit per female biomass index. However, the observations for 5 out of the 19 years considered in the present study were outside the 95% confidence interval of the fitted model, possibly due to a mismatch between the timing of larval hatch and the timing of the phytoplankton bloom, which could not adequately be addressed due to data limitations. KEY WORDS: Pandalid shrimp · Stock–recruitment relationship · Recruitment success · Temperature · Predation · Maternal effects · Subarctic seas Full text in pdf format PreviousCite this article as: Wieland K, Siegstad H (2012) Environmental factors affecting recruitment of northern shrimp Pandalus borealis in West Greenland waters. Mar Ecol Prog Ser 469:297-306. https://doi.org/10.3354/meps09794 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 469. Online publication date: November 26, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Effects of single or trickle Haemonchus contortus experimental infection on digestibility and host responses of naïve Creole kids reared indoor

The objective of this study was to compare the effects of the type of Haemonchus contortus experimental infection (trickle infection, TI versus single infection, SI) on feed intake, nutrients digestibility, parasitological and haematological measures, and plasma leptin in Creole kids. The animals were infected over 2 periods (challenge 1 and challenge 2) of 6 weeks each, corresponding respectively to the primary and the secondary infection. Periods prior infection (1 week each) were considered as controls. The primary infection was realized with 35 Creole kids (18.40±3.76kgBW) housed in individual boxes and fed a hay-based diet. The secondary infection continued with 29 kids (21.90±3.40kgBW) from the initial 35. A total of 6 kids and 8 kids were slaughtered for measuring nematode burden at the end of the primary and the secondary infection, respectively. Measurements of nutrients digestibility were made at 0, 3 and 5 weeks post-infection for both challenges. Faecal egg count (FEC), blood eosinophilia and packed cell volume (PCV) were monitored weekly. Feed intake (dry matter intake, DMI) and nutrients digestibility were negatively affected by H. contortus infection only during the primary infection. Plasma leptin changed significantly over time (P=0.0002) but was not affected by the infection type. Effect of infection type was observed only on crude protein digestibility during the primary infection, which was lower in the TI group (P<0.01). The overall level of blood eosinophilia was significantly higher in the TI group (P<0.0001) during both challenges. The overall FEC mean was significantly higher in the SI compared with the TI groups, during both challenges (P<0.02). These results were related to the mean female length significantly higher in the SI group compared with the TI group during challenge 1 (P=0.004), and the number of adult nematode significantly lower in the TI group compared with the SI group during the challenge 2 (P=0.05). The results showed that the response of Creole kids to H. contortus experimental infection was in part dependent on the type of experimental infection. Our data suggest that plasma leptin would not be involved in the response of Creole kids against H. contortus infection, as no relationship between its plasma level and the transient reduction in voluntary feed intake observed in both groups during the primary infection was observed.

Intraspecific density-dependent effects on growth and fecundity of Diplosentis nudus (Harada, 1938) Pichelin et Cribb, 2001 (Acanthocephala, Cavisomidae)

AbstractDuring June and July of 2007, a total of 130 specimens of the fish Rastrelliger kanagurta Cuvier (Teleostei, Scombridae), ranging between 19–31 cm in total length, were caught in the Red Sea off the coast of Sharm El-Sheikh, South Sinai, Egypt, and examined for infections by acanthocephalans (65 fish/month). Of this number, 29 (22.30%) were slightly or heavily parasitized by the acanthocephalan Diplosentis nudus (Harada, 1938) Pichelin et Cribb, 2001 (Cavisomidae); no other helminth parasites were found in the intestine of R. kanagurta. Twenty-nine infrapopulations of D. nudus, ranging from 23–218 individuals were collected from the infected fishes. These infrapopulations were distributed in a well-defined fundamental niche along the intestine of R. kanagurta, where the distribution of male worms was not random with respect to female worms size and position and suggests that the male-male competition for access to female may be intense and may select for large males. No correlation between fish size and infrapopulation size was observed. Correlations between female-to-male sex ratio and infrapopulation size, numbers of females and their mean lengths, numbers of males and their mean lengths, mean female length and mean male length within infrapopulation were very strong, and clearly suggest that as the infrapopulation size increased, the number of females and their mean lengths decreased and the number of males and their mean lengths increased. Combination of these results strongly suggests density-dependent effects and competition between male worms. The relationship between the mean female length or size and the number of eggs within its pseudocoel was strongly positive; egg production by female worm significantly decreases as the infrapopulation size increases, suggesting density-dependent reduction in female worm fecundity. Tendency for the variability in male testes size was not significant in infrapopulations of D. nudus. All of these results are discussed.

Size composition, monthly condition factor and morphometrics for fishery-dependent samples of Rioraja agassizi (Chondrichthyes: Rajidae), off Santos, Southeast Brazil

Specimens of Rioraja agassizi were collected monthly off Santos, Southeast Brazil, between latitudes 23º37'S and 27º40'S, from March, 2005 to March, 2006. A total number of 278 males and 1023 females were captured. Observed depth range was 10-120 m, being the species absent above 120 m. Sex ratio significantly favored females. The entire length range of R. agassizi was observed. Females ranged in length from 16.0 to 59.4 cm and males from 13.0 to 47.2 cm. Mean female length was significantly higher than that of males. For grouped length distributions, asymmetry patterns were observed in both sexes. Length-width functions were sexually dimorphic. Males with lengths &lt; 24.5 cm were relatively wider than females. Length-total weight curves were significantly different than length-gutted weight ones, in both sexes. Females were heavier than males for a given TL class. The angular coefficient b was significantly &lt;3 (negative allometry) in the males, and also for the females with exception of spring when b was &gt;3 (positive allometry). The monthly variation of the condition factor showed significant differences in both sexes.

Factors Influencing Sexual Size Dimorphism in Temperate Waterstriders

Sexual size ratios (mean female length divided by mean male length) of 12 species of temperate waterstriders in the subfamily Gerrinae (Hemiptera, Gerridae) are analyzed to test both potentially nonadaptive and adaptive hypotheses for the evolution of sexual size dimorphism. Females tend to be larger than males, and regression of female length on male length (both log-transformed) reveals significant hypoallometry for size dimorphism. Both adaptive and nonadaptive explanations for the evolution of this allometry are discussed. Of these, only a nonadaptive model is consistent with the available data. Two closely related genera, Limnoporus and Gerris, are included in the data set, but covariance analysis reveals no significant effect of phylogeny on patterns of variation in size dimorphism. It is suggested, however, that the basic female bias may reflect descent from a common, highly dimorphic ancestor, rather than adaptation within this taxon. Four adaptive hypotheses are considered. Comparisons of the development times of males and females reveal that the female-biased size dimorphism is not associated with protandry, and the developmental-constraints hypothesis is therefore rejected. The hypothesis that selection for migration by flight tends to reduce sexual size dimorphism is supported by intraspecific comparisons of long-winged and short-winged morphs. A positive correlation between mating duration and residuals from the body-size regression supports the hypothesis that loading constraints associated with prolonged pairing select for increased size dimorphism. The available data on mating systems and size-selective mating support the hypothesis that sexual selection for large males promotes reduced or even reversed size dimorphism in some species, whereas sexual selection for large females increases size dimorphism in other species. Thus, patterns of size dimorphism in this taxon may be influenced by at least three, potentially interacting, selective processes: selection for dispersal by flight, selection for reduced loading during prolonged pairing, and sexual selection. The relative influence of these factors in three groups of ecologically similar species is discussed. The general conclusions of this study are consistent with the results of recent comparative studies of size dimorphism in primates. In both taxa, sexual size dimorphism is most strongly influenced by potentially nonadaptive factors, and the residual variation reflects the action of several selective factors. The complexity of size-ratio evolution revealed by these studies suggests that patterns of sizeratio variation within and among taxa, or size ratios typical of single species, are unlikely to be satisfactorily explained by reference to single hypotheses or to selective hypotheses only.

Paternal Investment and Sexual Size Dimorphism in North American Passerines

Data from 106 species of North American passerines are used to test the hypothesis that an active male role in parental care is correlated with a reduction in sexual size dimorphism. The data show a negative correlation between an index of the male's involvment in parental care and the ratio of mean male length to mean female length (or wing length ratio). When polygynous or promiscuous species are excluded from the analysis, a similar negative correlation is still found. The results support models suggesting that sexual selection for increased male size is balanced by energetic constraints, including those imposed by paternal care.