Subscribe Now Subscribe Today
Abstract
Fulltext PDF
References
Research Article
 
Population Structure and Shell Morphometrics of the Gastropod Theodoxus macri (Neritidae: Prosobranchia) from Azraq Oasis, Jordan



Ali Z. Elkarmi and Naim S. Ismail
 
ABSTRACT

A total of 371 specimens of the freshwater gastropod Theodoxus macri (Sowerby, 1849) (Neritidae: Prosobranchia) from Azraq Oasis, Jordan, were studied for age, growth and shell morphometrics. The results show the life span to be four years. The mean observed lengths of the four age cohorts range from 3.295 to 7.707 mm. Theoretically, using Von Bertalanffy’s and Richard’s growth formulae, the maximum length of this snail may reach 17.187 and 12.930 mm, respectively. Shell and dry body weights averaged 44.4 and 36.05 mg, respectively. The relationships of the shell length to shell and dry body weights are curvilinear. However, the relationships of the shell length to shell width, aperture length and aperture width are linear. The relative coefficient (Kn) was 1.008 and 0.999 for young (age groups 1-2) and old (age groups 3-4) snails, respectively.

Services
Related Articles in ASCI
Similar Articles in this Journal
Search in Google Scholar
View Citation
Report Citation

 
  How to cite this article:

Ali Z. Elkarmi and Naim S. Ismail , 2006. Population Structure and Shell Morphometrics of the Gastropod Theodoxus macri (Neritidae: Prosobranchia) from Azraq Oasis, Jordan. Pakistan Journal of Biological Sciences, 9: 549-552.

DOI: 10.3923/pjbs.2006.549.552

URL: https://scialert.net/abstract/?doi=pjbs.2006.549.552

INTRODUCTION

Theodoxus is a neritid snail succeeded in invading freshwater habitats. These snails are usually subglobose or hemispherical, have few whorls, very reduced spires and very large body whorl. Two freshwater species were reported from Jordan, T. jordani and T. macri (Burch, 1985). Dagan (1971) contended that both species of Theodoxus are the same, a conclusion based on details of the opercular apophyses and the central teeth of the radula. However, T. macri is uniformly black or dark purple in color, while, T. Jordani is zebrated having red or brown to deep purple or dark black zig-zag stripes on a white or yellow background (Burch, 1985). Both species are common in all freshwater habitats of Jordan. In Azraq Oasis, T. macri is mostly found in spring pools, ponds and swamps. The present research aims at providing more information on the population structure and shell morphometrics of T. macri from Azraq Oasis.

MATERIALS AND METHODS

Study area: Azraq Oasis is a semi-desert area in the East Jordanian Desert 85 km east of Amman, the capital of Jordan. It is the only permanent water in this region. It’s water is supplied by two springs, one in North Azraq and the other is in South Azraq. Azraq pools are infested with several snail species. Most predominant are Melanopsis praemorsa, Melanoides tuberculata and Theodoxus macri.

Sampling and analysis: A total of 371 Theodoxus macri (Sowerby, 1849) (Neritidae: Prosobranchia) snails were collected by hand picking from Azraq Oasis pools. In the laboratory, shell length, shell width, aperture length and aperture width were measured using vernier calipers, to the nearest 0.1 mm. The shells of about 310 snails were separated from soft tissues and dried to constant weights at 100°C. The dry weights of both the shell and soft body were weighed using an electrical digital balance accurate to 1 mg. Measured snails were divided into size groups of length intervals which were estimated using histogram plots that show normal distribution of length. Normality was tested at 95% confidence level. These histograms used to estimate the possible life span of T. macri snails.

The growth in length of T. macri was theoretically calculated using the Von Bertalanffy’s Growth Formula (VBGF) (Lt = L∞ [1-e –k (t-t0)]) and the Richard’s Growth Formula (RGF) ( Lt = L∞ [1-A*e –kt]). Lt is the length at age t, A = 1 – (minimum length/maximum length), k is the growth coefficient and t0 is the length at which the age is theoretically nil. The constants L∞, k and t0 were calculated using the Quasi-Newton method (Ostle and Mensing, 1975) to the age-length data. For comparison with VBGF and RGF, the observed age length data were fitted to a linear regression equation. The relationships of the shell length to dry body weight and shell weight were described using a power regression equation (Ott, 1984).

The relative coefficient of condition (Kn) which measures the degree of fitness and suitability of the environment with regard to feeding condition was also estimated (Le Cren, 1951). Kn was calculated as: Kn = X/aLn where X represents the dry body weight, L is the shell length, a and n are the coefficients of the power regressing equation.

The relationships of the shell length to shell width, aperture length, aperture width, shell weight, dry body weight, total weight, ratio of aperture width to shell length, ratio of aperture length to shell length and ratio of shell width to shell length were studied using regression analysis.

RESULTS

Age and growth: The frequency distribution of shell length of the collected snails which fits normal distribution indicates the presence of four age cohorts for T. macri (Fig. 1). The mean observed length at each of these age cohorts was 3.295, 4.984, 7.707 and 10.281 mm (Table 1). Calculated shell lengths using VBGF and the linear method were highly correlated with the observed values (R2 >0.96) (Table 1). However, this correlation was 78.3% using RGF. Thus, it is expected that this snail may survive to four years. The annual observed increase in length ranges from 1.689 to 2.723 mm. Theoretically, the increase ranges from 1.835 mm in old snails to 2.861 mm in young ones using the VBGF and from 1.058 to 1.650 mm using RGF. The theoretical growth parameters of T. macri were similar using VBGF and RGF (Table 2 ). The theoretical maximum growth was 17.187 and 12.930 mm and the growth coefficients (k) were 0.218 and 0.222. The length at to was calculated to be 0.194.

Length-weight relationship: Collected T. macri snails range in length from 2.20 to 11.00 mm, with a mean value of 5.628 mm.

Fig. 1: Frequency distribution of estimated length groups of Theodoxus macri from Azraq Oasis showing expected normal distribution (n = 371)

Their shell and dry body weights range from 2 mg to 360 mg with an average of 44.4 mg and from 1.0 mg to 150 mg with an average of 36.05 mg, respectively. Increase in shell and body weights was slower in young snails than older ones.

Table 1:
Observed and calculated shell lengths (in mm ) of various age groups of Theodoxus macri from Azraq Oasis using Von Bertalanffy’s Growth Formula (VBGF) and the Richard’s Growth Formula (RGF) and Linear regression equation

Table 2:
Growth parameters of Theodoxus macri from Azraq Oasis using Von Bertalanffy’s Growth Formula (VBGF) and the Richard’s Growth Formula (RGF)

Fig. 2: The relationships of the shell length to shell, body and total weight of Theodoxus macri from Azraq Oasis

Fig. 3: The relationship between the total weight and the dry body weight of Theodoxus macri from Azraq Oasis

Fig. 4:
The relationships of shell length to shell width, aperture length and aperture width of Theodoxus macri from Azraq Oasis

This produced curvilinear relationships of the shell length to both shell and dry body weights (Fig. 2).

Table 3: Measurements (means in mm±SD) of length (SHL), shell width (SHW) aperture length (APL) and aperture width (APW) of various age groups of Theodoxus macri from Azraq Oasis

Fig. 5:
The relationships of the shell length to ratios of shell length (SHL) to each of shell width (SHW), aperture length (APL) and aperture width (APW) of Theodoxus macri from Azraq Oasis

The power regression equations for these relationships are:

X=0.281 (L) 3.199
X1=0.189 (L) 3.680
X2=0.114 (L) 2.712

Where X, X 1 and X2 represent the total, shell and dry body weights, respectively and L represents the shell length. The relationship of the total weight to dry body weight was linear (Fig. 3). The relative coefficient of condition (Kn) which measures the progression of body weight and length was measured for young and old snails (age groups 1 and 2 and 3 and 4, respectively ). It was 1.008 and 0.999 for both groups, respectively.

Shell morphometrics: The mean shell length of age groups 1 to 4 of T. macri ranges from 3.295 to 10.281 mm. The shell width ranges from 2.684 to 7.644 mm, aperture length from 2.203 to 5.713 mm and aperture width from 1.468 to 3.781 mm (Table 3). The relationships of the shell length (L) to shell width (W), aperture length (AL) and aperture width (AW) are linear (Fig. 4). The regression equations for these relationships are:

W=0.039 + 0.713L
AL=0.076 + 0.524L
AW=0.073 + 0.328L

The ratios of the shell width, the aperture width and the aperture length to shell length decrease with age (Fig. 5). This may indicate that this snail become more elongate with age.

DISCUSSION

The frequency distribution of the shell length of collected Theodoxus macri snails from Azraq Oasis indicated the presence of four age cohorts. These snails range in length from 3.3 to 10.3 mm. Theodoxus jordani snails collected from Yarmouk River ranged in size from 1 to 20 mm and 74-84% of them measured 6-13 mm (Abel-Hafez and Ismail, 1987). Two peaks of young snails (4 mm long) appeared during September and March. These snails grew at a rate of about 6 mm per year (Abel-Hafez and Ismail, 1987). In the present study this snail increased in length at a rate of 1.689 to 2.723 mm annually. Melanopsis praemorsa from Yarmouk River increased by 3-4 mm between January and December and ranged in size from 3-27 mm (Ismail and Abel-Hafez, 1987). Higher rates of increase were reported from Drupella cornus snails from the Gulf of Aqaba (Ismail et al., 2000). These snails grew at a rate of 3.7-6.8 mm annually. The limpet, Cellana radiata, from the Gulf of Aqaba grew at a rate of 4.0-9.0 mm annually (Ismail and Elkarmi, 1999).

Increase in shell and dry body weights of T. macri was slower in young snails than older ones of in the present study. This produced curvilinear relationships of the shell length to both shell and dry body weights. This was also true for D. cornus (Ismail et al., 2000 ) and C. radiata (Ismail and Elkarmi, 1999). However, power regression equations for these relationships for different snails were different. Moreover, the relationship of the dry body weight to shell weight was linear for both T. macri in the present study and D. cornus from the Gulf of Aqaba.

The relationships of the shell length to shell width, aperture length and aperture width were linear for both T. macri from Azraq and D. cornus (Ismail et al., 2000 ). However, linear regression equations were different for both snails. Similarly, the shell length to shell width relationship of C. radiata was also linear (Ismail and Elkarmi, 1999).

REFERENCES
Abel-Hafez, S.K. and N.S. Ismail, 1987. Population dynamics of Theodoxus jordani snails in Yarmouk river, Jordan and its seasonal infection with larval trematodes. Arab Gulf J. Sci. Res., 5: 463-470.

Burch, J.B., 1985. Handbook on Schistosomiasis and Other Snail-Mediated Diseases in Jordan. University of Michigan, Jorden.

Dagan, D., 1971. Taxonomic discrimination between certain species of the genus Theodoxus (Gastropoda, Neritidae). Isr. J. Zool., 20: 223-229.

Ismail, N.S. and A.Z. Elkarmi, 1999. Age, growth and shell morphometrics of the limpet Cellana radiata (Born, 1778) form the Gulf of Aqaba, Red Sea. Venus, 58: 61-69.

Ismail, N.S. and S.K. Abel-Hafez, 1987. Population dynamics of Melanopsis praemorsa (L. 1785) (Thiaridae) snails in Yarmouk river, Jordan and its seasonal infection with larval trematodes. Arab Gulf J. Sci. Res., 5: 287-299.

Ismail, N.S., A.Z. Elkarmi and S.M. Al-Moghrabi, 2000. Population structure and shell morphometrics of the corallivorous gastropod Drupella cornus (Gastropoda: Prosobranchia) in the Gulf of Aqaba, Red Sea. Ind. J. Mar. Sci., 29: 165-170.
Direct Link  |  

Le-Cren, E.D., 1951. The length-weight relationship and seasonal cycle in perch (Perca fluviatilis). J. Anim. Ecol., 20: 201-210.

Ostle, B. and R.W. Mensing, 1975. Statistics in Research. Iowa State University Press, Iowa, USA., pp: 206.

Ott, L., 1984. An Introduction to Statistical Methods and Data Analysis. 1st Edn., Duxbury Press, Boston, pp: 482.

©  2018 Science Alert. All Rights Reserved
Fulltext PDF References Abstract