International Research Journal of Biological Sciences ___________________________________ ISSN 2278-3202Vol. 2(1), 1-6, January (2013) Int. Res. J. Biological Sci. International Science Congress Association 1 Realized Fecundity in the First Brood and size of Eggs of Chinese Mitten crab (Eriocheir sinensis)- Laboratory StudiesCzerniejewski Przemys\naw1 and De Giosa MarcelloDept. of Fisheries Management, Westpomeranian University of Technology in Szczecin, Krolewicza 4, PL–71–550 Szczecin, POLAND Dipartimento di Matematica, Universita' di Bari, via Orabona, 4, 70125 – Bari, ITALY Available online at: www.isca.in Received 29th June 2012, revised 3rd August 2012, accepted 4th September 2012Abstract The Chinese mitten crab was collected from north part of Szczecin Lagoon (The Odra river estuary)within 12 October–6 December 2008 and 5 October–3 December 2010, to investigate some reproduction aspects in laboratory. This study was carried out to estimate the fecundity during oviposition period in first brood of Chinese mitten crab, eggs size and describe relation to various morphometric characters such as carapace width and height and body weight. The results showed that the fecundity of Eriocheir sinensis range from 141100 to 686200 eggs (mean 461100 eggs per female) with first brood, and mean eggs size were 371,4 µm (range 361 - 375µm). All the morphometric characteristics studied showed positive correlation with fecundity and the degree of relationship varied considerably. Among these, the carapace width was found to be the best morphometric character for predicting the fecundity of Chinese mitten crab. Keywords: Chinese mitten crab, realized fecundity, morphometric characters, size of eggs. Introduction The study of fecundity of any species is important to have a full understanding of its biology and population dynamics. Fecundity is in general used to describe the number of eggs produced by an individual female. However, a more complete definition has been given by Corey and Stechey and Somersfor crayfish, who defined fecundity as: i. potential fecundity, that is the number of oocytes counted in the ovaries; ii. realized fecundity, that is the number of eggs actually extruded and attached to pleopod; and iii. actual fecundity, which refers to the number of juveniles hatched. Fecundity of crabs varies from species to species and also varies within the same species due to different factors such as age, size, nourishment, ecological conditions of the water body4,5,6. In crabs, studies on the relationship between size of some morphological features and fecundity are scanty. Positive correlation between carapace width and fecundity was reported for crabs such as Paralithodes camtschatica, Clibanarius antillensis, C. sclopetarius and C. vittatus and Carcinoplax vestita. Similar relationship has been observed between carapace length and fecundity in Platyxanthus patagonicus. According to the Global Invasive Species Database, the Chinese mitten crab is one of the 100 “World’s Worst” invaders. Because of the profound economic and ecological effects of the invasive populations in Europe and in the San Francisco Bay area, there is much concern about the potential impacts of this species in Europe and along the east coast of the USA10,11. Despite its potential commercial importance as a billion dollar aquaculture species in China12, and a global history of aquatic invasion13, the scientific literature on the fecundity, reproduction and relationship between the morphological features and fecundity is still limited. Only Kobayashi and Matsura14, and Kobayashi15 gave some interesting data about reproduction in E. japonicus (genus Eriocheir). The present study was carried out to investigate realized fecundity in the first brood of Chinese mitten crab and its relationship to various morphometric characters such as carapace width and height and body weight. Material and MethodsA total of 259 Chinese mitten crabs were caught as a by- catch in fyke nets, within 12 October – 6 December 2008 and 5 October – 3 December 2010 in the north of Szczecin Lagoon (figure 1). Crabs were sexed, resulting in 115 males and 144 females. Live crabs were delivered to the laboratory and weight (W) was measured to 0.1 g on an Axis B2000B (Axis Co., Poland) electronic scales. Carapace width (CW) and height (CH) were measured to 0.01 mm, with computer–interfaced electronic callipers. The collected animals were divided into four separate holding (1000l) tanks for both sexes at salinity 15 ppm, and temperature 8-12C. After 14-21 days, a pair of crabs (female and male) were transferred from tanks to smaller aquaria (40 x 40 x45 cm) containing seawater at salinity 25 ppm. The animals were maintained at a 12 h:12 h light-dark cycle16. The water quality in the tanks and aquaria was maintained using a flow-through system (2L/min) and gentle aeration. Observations were made over a 60 min. period, and types of mating interaction were noted16. When crabs had no International Research Journal of Biological Sciences ________________________________________________ ISSN 2278-3202 Vol. 2(1), 1-6, January (2013) Int. Res. J. Biological Sci. International Science Congress Association 2 physical contact, or had contact without mating after 5 days, female and male were changed. After mating males were replaced from aquaria, and females were monitored for spawning six times a day. Eggs were removed from the pleopods of ovigerous female using a soft-hair brush, and the collected egg mass was preserved. Fecundity (FEC) was estimated by the gravimetric method17, using a subsample of 5% by weight of the egg mass. A sample of 5 eggs was taken from different regions of pleopods, and the egg diameters (ES) were measured using an ocular micrometer scale under a microscope stereoscope. An explorative data analysis process was applied to data to investigate the presence of outliers and the type of relationships between variables. The relationship between FEC and each in turn of the explanatory variables CW, CH and W was modeled by fitting normal linear regression to data. For each model, significance of the regression line slope was verified using the t-test procedures18. Models with different explanatory variable were compared using the determination coefficient r-squared: bigger the r-squared, better the model. A graphical validation process19 was applied to the choosen optimal model to assess normal linear regression assumptions: homogeneity, normality, independence. Influence of observations was evaluated on the basis of Cook’s distance. The relationship between ES and explanatory variables was also investigated following the same procedures. Results and Discussion Of the 259 crabs collected from the Szczecin Lagoon, 144 were females and 115 were males, giving a sex ratio of 1:0.80. The monthly variation in sex ratio is shown in table 1. Females were more abundant than males in the autumn months of October and November and males were dominant in December. However a Chisquare test (Chi-Sq = 1.604; d.f. = 2; p-value = 0.448) showed that sex ratio may be considered independent of the catching month. Out of a total of 144 females catching in 2009-2010, mating occurred only for 42 individuals (29,8%). Individual fecundity of Eriocheir sinensis on the first brood ranged from 141 100 to 686 200 eggs per female. Mean fecundity was 461 100 ± st.err. 16871.65 eggs. Egg size ranged from 361 to 378 µm. Mean egg size was 371.40 ± st. err. 0.64 µm. The carapace width of the crab specimens used for fecundity prediction ranged from 46.68 to 80.44 mm (mean 68.17 mm ± st. err. 1.04), the carapace height ranged from 22.11 to 43.31 mm (mean 35.71 mm ± st. err. 0.61), and weight ranged from 47.10 to 219.30 g (mean 142.40 g ± st. err. 6.06). A summary of the data for each variable is shown in table 2. Figure-1 Location of Chinese mitten crab collection sites in the Szczecin Lagoon International Research Journal of Biological Sciences ________________________________________________ ISSN 2278-3202 Vol. 2(1), 1-6, January (2013) Int. Res. J. Biological Sci. International Science Congress Association 3 Table-1 Sex ratio of the Chinese mitten crab Month Females Males October 42 36 November 86 61 December 16 18 Together 144 115 Table-2 Summary statistics for FEC, ES, CW, CH and WMin. 1 st quart. Median mean±st.err. 3 rd quart. max. FEC 141100 397800 479500 461100±16871.65 540900 686200 ES 361 369 372 371.40± 0.64 375 378 CW 46.68 64.78 69.47 68.17±1.04 73.85 80.44 CH 22.11 33.18 36.48 35.71±0.61 38.42 43.31 W 47.10 116.90 148.80 142.40±6.06 172.50 219.30 Boxplots and Cleveland dotplots (not shown here) didn’t show presence of outliers in any of the considered variables. Explorative plots of fecundity (FEC) against each of the considered explanatory variables showed a strong linear relationship. Three linear regression models were fitted to data. FEC was assumed as the dependent variable and each time one of carapace width (CW), carapace height (CH) and crab weight (W) was assumed as the explanatory variable in turn. In figure 2, plots of data with estimated regression lines are represented. Estimated slope, standard error, t statistic, p-value and r-squared are reported in table 3 for each considered model. All linear relationships were positive and significant (p0.0001). Based on the r-squared values, we concluded that the optimal fitted model was that assuming CW as the explanatory variable: FEC = -572757.4+15165.8 * CW+N(0,) with estimated standard error = 38230 on 40 degrees of freedom and r-squared = 0.8807. Model validation was based on the inspection of four plots: residuals against fitted values plot, normal Q-Q plot (standardized residuals versus theoretical quantiles), square root of the absolute value of standardized residuals against fitted values and standardized residuals against leverages. All investigated plots (not shown here) did not indicate any problem with model assumptions (homogeneity, independence, normality) and influential observations. Explorative plots of ES data against each of the considered explanatory variable data didn’t suggest any particular relationship (figure 3). Three linear regression models were fitted to data. ES was assumed as the dependent variable and each time one of CW, CH and W was used as the explanatory variable in turn. For all models, the slopes were found to be not significantly different from 0 (at 5%). A large part of the benthic fauna associated with estuarine and marine waters is formed by brachyuran crustaceans. Some authors suggested that it is caused by high fecundity of that species 20. Kwei21 reported 1.9-2.8 million eggs in Callinectes latimanus, while Guillory et. al.22 documented mean fecundity of 3.2 million eggs for Callinectes sapidus. However, some of the brachyuran crabs are characterized by lower fecundity4,23. Some species of the Majidae had significantly lower numbers of eggs per brood than others Brachyura crabs but the majid's lower number of eggs per brood was compensated by a greater than average number of broods per year, resulting in approximately the same average fecundity per year. Multiparous brachyurans are known to release up to 10 broods annually4,24,25, and one brood per instar per season appears to be the rule in most species of Cancer26. In genus Eriocheir, female produce multiple broods during the reproductive season27. Kobayashi15 found that Eriocheir japonicus had up to 3 broods in a single reproductive season, but fecundity in the first brood is more than in the later oviposition. In Eriocheir japonicus, total fecundity ranged from 230 000 to 980 000 eggs/female, but in first brood from 120 000 (40mm in CW) to 600 000 (70mm)15. Female mitten crabs are highly fecund too, producing between 100 000 and 1 milion eggs13. In our experiment, fecundity in first brood ranged from 141100 to 686200 eggs per female (mean 461100 eggs per female). When compared to other grapsid crabs, size and fecundity of the first oviposition of E. sinensis are larger4,24,28. Probably, large fecundity per brood with large maturity size compensates for the decrease in their brooding time and lifetime fecundity15. The reproductive characteristics of a species are a result of the interaction between various endogenous and exogenous factors26, such as temperature, salinity, food availability, photoperiod and lunar cycles29,30. Strong size fecundity relationships are found in brachyuran families. Fecundity of Chinese mitten crab is significantly linearly correlated with carapace width and height and weight. The fecundity in first brood of Eriocheir sinensis increased with increase in carapace width (CW) and height (CH) and weight of International Research Journal of Biological Sciences ________________________________________________ ISSN 2278-3202 Vol. 2(1), 1-6, January (2013) Int. Res. J. Biological Sci. International Science Congress Association 4 crabs (W). Similar relationship was observed between CW and fecundity in Geryon fenneri31, in Scylla olivacea32 and in Cancer paguru. In a study on the reproductive cycle of P. pelagicus off southern Australia, Kumar et al.33 reported a rise in fecundity by 83.9% with an increase in carapace width from 105 mm to 125 mm. Positive correlation between weight and fecundity with high r-squared value (0.908) was reported by Haddon34 in Ovalipes catharus. Villegaset al.35 analyzed that relationship on the shrimp Penaeus monodon and Sharma and Subba36 on the freshwater prawn Macrobrachium lamareii also showed positive relationship between body weight and fecundity, but with low r-squared. However, in Chinese mitten crab, based on the r-squared values, the carapace width was found to be the most suitable characteristic for predicting fecundity. The strong positive correlation between fecundity and carapace width of Chinese mitten crab leads us to the contention that the animal size could be a potential allometric constraint on the reproductive output, as postulated in other brachyurans. Fecundity is determinate not only by female body size, but also by average egg size. Egg size in brachyurans is not generally correlated with adult size37. In most of species of crabs egg size ranged between 250µm and 450µm, but in S. curacaoense and A. miersii have much larger eggs (600 -700 µm), which explain their low fecundity38. The measurement of the egg diameter of Chinese mitten crab showed variations in egg sizes. The diameter ranged from 361 to 375 µm with a mean of 371.4 µm (±0,64). According to Dittel and Epifanio13 eggs of Chinese mitten crab are about 350-380 µm in diameter. There was not significant correlation between egg size and carapace width (CW) and height (CH), and individual weight in this species. Sex ratio in a majority of species is close to unity, despite some variations between populations of a species, and from year to year in the same population39. The overall sex ratio in Eriocheir sinensis differed from the expected 1:1 ratio, but not significantly. In Odra estuary in autumn months were higher occurrences of male than female40. Table-3 Explanatory variable, estimated slope, standard error, t-statistic, p-value and r-squared for each considered regression model Explanatory Variable Estimated Slopes Standard Error t-statistic p-value r-squared CW15165.8 882.5 17.185 0.0001 0.8807 CH 24907 1961 12.704 0.0001 0.8014 W 2491.6 196.7 12.665 0.0001 0.8004 Figure-2 Plots of FEC against each explanatory variable (CW, CH and W) with estimated regression lines International Research Journal of Biological Sciences ________________________________________________ ISSN 2278-3202 Vol. 2(1), 1-6, January (2013) Int. Res. J. Biological Sci. International Science Congress Association 5 Figure-3 Plots of ES against each explanatory variable (CW, CH and W) Conclusion Female mitten crabs are highly fecund, producing between 141100 and 686200 eggs (mean 461100 eggs per female) in first brood. Fecundity in E. sinensis increased with female size. The optimal fitted model was that assuming CW as the explanatory variable: FEC = -572757.4+15165.8 * CW+N(0,) with estimated standard error = 38230 on 40 degrees of freedom and r-squared = 0.8807. The measurement of the egg diameter showed variations in egg sizes. The diameter ranged from 361 - 375µm (mean eggs size were 371,4 µm). All the morphometric characteristics studied showed positive correlation with fecundity and the degree of relationship varied considerably. Among these, the carapace width was found to be the best morphometric character for predicting the fecundity of Chinese mitten crab. References 1.Lagler K.F., Studies of freshwater biology, Ann Arbor. 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