Gonad development and reproductive pattern of the fighting conch Strombus pugilis (linee, 1758) (gastropoda, prosobranchia) from Campeche, Mexico.

ABSTRACT The processes of gonad development through a year are analyzed for Strombus pugilis from Seybaplaya, Campeche. During gametogenesis second order oocytes appear close to the wall of the follicles, with a diameter 90-250 [micro]m. The cytoplasm is granular, the nucleus is located on the periphery, with a diameter of 15-35[micro]m, a nucleolus 7-8 [micro]m. Spermatozoids have an acrosome of 5-7 [micro]m, shaped like a coma. In females gametogenesis was registered in two pulses, with 2 peaks of 60%, February to June and September to October. Mature females were found during the 8 months of sampling with peaks during May and August (80%). Spawning was discontinuous, suggesting storage of mature gametes for the fight time to spawn. In males gametogenesis was present in a low percentage from March to October, with a maximum of 20%. Maturity was present on just a 10% during July, with constant spawn through the year. Copula has been observed only during egg laying seasons; males seem to keep mature sperms in the prostate gland. Strombus pugilis from the coasts of Campeche presented a fast gonad recovery for males, requiring longer for females. Having missed most of the autumn and early winter months leaves a big gap on the processes of gonad recovery and early gametogenesis. Apparently there is no correlation between salinity, temperature and the reproductive cycle, but this population has the potential for reproducing through the year.

KEY WORDS: Strombus pugilis, reproduction, gonad, conch 

INTRODUCTION

The study of the reproductive cycle of commercial gastropod species was undertaken as part of the requirements for the management of conch resources from Campeche, Mexico. Conch fishery of Campeche supports a mean production of 700 tons a year made up of eight species, of which Strombus pugilis (Linee, 1758) represents 20%. Given its abundance, it has been considered a resource with potential to increase production (Baqueiro et al. 1999, Navarrete et al. 2000).

S. pugilis is one of six species of strombids found on the Atlantic coast of Mexico. The only sexual external characteristic is the presence of the verge in males and a copulatory ditch on the dorsal surface of the female foot (Reed 1995a and Reed 1995b). Reed (op. cit.) has described the anatomy of the reproductive system of male and female and the microscopic characteristics of the gonads, with emphasis on female masculinization, but the gametogenic development and cycle were not described. Bradshaw-Hawkins (1982) describe the reproductive cycle from Barbados.

The reproductive cycle is a population characteristic determined by the environment (Baqueiro 1998), which may vary from place to place and from year to year. It might be determinant of the population renewal, for stock dependent recruitment, but it may also be locally unimportant when recruitment depends on meta populations (Young 1991, Rice & Peckerik 1992). S. pugilis populations on the coast of Campeche are located on open waters, from 3 to 25 m depth, giving an ample possibility of larval dispersion. A meta-population recruitment process is assumed, although Deleo (1996) has found that clam populations from exposed beaches may be stock dependant. Even though, the reproductive cycle of a population can give some light on the availability of larvae through the year.

MATERIALS AND METHODS

Twenty adult organisms, with a well formed lip, were collected for 8 months from July 1996 to July 1997 from Seybaplaya, Campeche (Fig. 1). Conchs were collected by SCUBA diving from 3-6 meters depth. Animals were transported alive in an ice chest with seawater. At the laboratory each animal was placed for 15 sec in a microwave oven at maximum power for fixation and extraction of soft parts from the shell (Berg & Adams 1984). Previously the weight of the whole animal was recorded. After extraction, the shell was measured and the weight of the shell and soft parts was recorded separately. Observations were made on the macroscopic features of the gonad in relation to the visceral mass. The top two or three spirals were cut off to dehydrate with alcohol for paraffin embedding, chloroform was used as clearing and transition agent. Harris Hematoxilin and acid eosin were used for staining of 10-[micro]m sections (Luna 1968).

[FIGURE 1 OMITTED]

RESULTS

Gonad Development at Macroscopic Level

At macroscopic level, female gonads at rest have a smooth appearance, of white thin tissue. As it matures, the tissue takes a granular appearance, with a color that goes from cream yellow to a brownish orange in ripe females. In males the rest stage has the same appearance as females, changing to a milky cream through gametogenesis and to bright orange when the animals are ripe.

The smallest animal in gametogenesis was a male 63-mm shell length. Masculinized females were larger than males and females, with a heavier shell and a significant larger weight of the soft parts. There was no significant difference between males and females in length or shell diameter or mean and maximum weight, except for minimum shell weight, that was significantly larger in females, and was reflected on the minimum total weight (Table 1).

Gonad Development at Microscopic Level

Females

Oogonia are adhered to the follicle wall; they are oval in shape, with a diameter 5-40 [micro]m; the cytoplasm is clear; the nucleus occupies most of the lumen of the cell. First order oocytes are found close to the follicle wall, they have a diameter 40-85 [micro]m; the cytoplasm is heavily vacuolated, giving a granular appearance; the nucleus and nucleolus also have a granular appearance with a diameter 12-25 [micro]m and 5-10 [micro]m, respectively. Second order oocytes are also close to the wall; their diameter is from 90-130 [micro]m; cytoplasm is granular; nucleus is 15-25 [micro]m, with a nucleolus 5-8 [micro]m. Mature oocytes are found at the center of the follicle, with a diameter 135-250 [micro]m, cytoplasm is totally occupied by reserve material, the nucleus is 25-60 [micro]m in diameter and nucleolus 5-12 [micro]m.

During the rest stage the gonad is composed of reticular connective tissue. The follicles are irregular structures of germinal tissue, characterized by acidophilus staining nuclei that occupy most of the cells' lumen (Fig. 2a). There are no differences between male or female structures. During gametogenesis, gonads occupy 30% of sections, the follicles are well defined with diameter 106-160 [micro]m (Fig. 2b, c). Maturing oocytes are surrounded by smaller ones that act as nutritious cells. Oogonias, first and second order oocytes are clearly differentiated. As gonads mature occupying 40% to 50% of the section, the follicles are 230-1800 [micro]m, no connective tissue can be seen between the follicles, and some of them fuse to form a large lumen, with ovae of granular cytoplasm (Fig. 2d). During spawning follicles are 150-1700 [micro]m, of irregular shape, partially empty with their walls frequently broken. Some oogonias and oocytes may be found close to the follicle walls, some ovae have busted walls and a few phagocytes may be found among them (Fig. 2e).

[FIGURE 2 OMITTED]

Males

Spermatogonias are 5-7 [micro]m in diameter; they are part of the follicle wall; the nucleuses are elongated occupying most of the cell lumen, 3 x 7 [micro]m. First order spermatocyts are oblong cells 12-15 [micro]m, with nucleus 5-7 [micro]m; they are found close to the follicle wall. Second order spermatocyts cells are 8-10 [micro]m with very little cytoplasm, the nucleus occupying most of it, with a diameter 5-6 [micro]m, they form packets towards the center of the follicle. Spermatids are 4-5 [micro]m with a 2-[micro]m nucleus; they are round to oblong in shape, forming packets toward the center of the follicle. Spermatozoa have a conical, curved head 6-7-[micro]m long and 2-[micro]m wide; they form compact packets at the center of the follicle, with tails towards the lumen.

During gametogenesis, follicles grow up to 800 [micro]m in diameter, and cells in all development stages can be seen with a dominance of first and second order spermatocyts (Fig. 3b to c). During maturity follicles frequently fuse, with spermatozoids occupying the lumen and some spermatocyts close to the follicles walls (Fig. 3d). As spawning advances follicles are partially emptied; the walls burst forming large irregular lumens with cells in all stages, most of the lumen is empty, and some spermatozoas are seen towards the center. Phagocytes are abundant on the connective tissue (Fig. 3e).

[FIGURE 3 OMITTED]

Post spawn is similar in both sexes; the gonadic tissue is occupied by reticular connective tissue. Follicles are broken and some reproductive cells can be seen in different stages of development. Numerous phagocytes are among the rest of the follicles and gametes. Any remaining gametes show autolysis with broken and wrinkled walls. The connective tissue close to the outer wall of the gonad has a packed appearance (Fig. 2f, 3f)

Reproductive Cycle

Females and males presented two rest periods after or during spawn; in females it goes from May to October with maximum of 40% during July (Fig. 4), whereas in males it extends from March to October with a maximum of 25% during the same month (Fig. 5). In both sexes rest was not registered during August.

[FIGURES 4-5 OMITTED]

In females, gametogenesis was registered in two pulses, with two peaks of 60% February to June and September to October. A large percentage of them were found mature during the whole year, with two peaks of 80% in May and August. Spawning was discontinuous, with 4 pulses of low intensity: February and June 10%, August and October 20%. Post spawn was inconspicuous with 15% during February and 30% in October (Fig. 4).

In males, gametogenesis was present in a low percentage from March to October, with a maximum of 20% in July. Maturity was only observed during July (10%). Spawn was preset through the year in over 70% of the male population, with a maximum of 100% in August and 2 periods of low intensity, July (15%) and October (40%). Post spawn was registered in 3 pulses with peaks in February and July (30%), and October 60% (Fig. 5).

Sex Ratio

There was a dominance of females over males, except during July, 2000, when there were more males than females (Table 2). Masculinized females were detected only during September and February, reaching under 16% in September, but with just 3% in average.

Gonad development in females is very similar to the outlined oogenesis described by Fretter and Graham (in Webber 1977), with some oocytes acting as accessory cells, whereas in males spermiogenesis conforms to the general development for archeogastropoda with no oligopirine spermatozoa (Webber, op. cit.). Gonadic development, for both sexes, is similar to what was described by Aldana Aranda et al. (2003a, 2003b) for S. gigas.

The constant presence of a few males in gametogenesis and the large percentage of spawning organisms through the year suggest a fast gonad recovery, whereas the absence of a maturity stage implies that spawning takes place as gametes mature. Females show different reproductive behavior. Where there is a constant presence of many animals in gametogenesis denotes a slow gonad recovery, apparently keeping mature eggs for the right time to spawn. The reproductive behavior of this population coincides with the reproductive potential reported by Bradshaw-Hawkins (1982) for a Barbados population.

As copulation has only been observed during egg laying season, apparently males store mature sperm in their prostate gland.

When average temperature and salinity are considered, only female spawn coincides with periods of falling salinity, although some spawning females were detected during June, when salinity reaches its highest. Apparently there is no correlation between salinity, temperature and the reproductive cycle.

The dominance of females in the population (Table 2) and seasonal spawning, determines the reproductive behavior of the population. With peaks of gametogenic activity, a constant presence of mature organisms and a long spawning season, with peaks in spring and summer (Fig. 6), egg masses have been found by the authors through the year with higher abundance from March to September.

[FIGURE 6 OMITTED]

Strombus pugilis from the coasts of Campeche has a fast gonad recovery. This population has the possibility of reproducing through the year. Apparently, a recovery season is present during autumn and winter, which was partially evident during September and February. Having missed most of autumn and winter this study leaves a big gap on the reproductive cycle.

LITERATURE CITED

Aldana Aranda, D., E. Baqueiro Cardenas, I. Martinez Morales, R. I. Ochoa Baez & T. Brul6. 2003a. Gonad behavior during peak reproduction period of Strombus gigas from Banco Chinchorro. Bull. Mar. Sci. 73(1):241-248.

Aldana Aranda, D., Baqueiro Cardenas E., Martinez Morales I, Ochoa Baez R. I. and Brule T. 2003b. Reproductive patterns of Strombus gigas from Alacranes reef versus Chinchorro Bank of Mexico. 54th Gulf and Caribbean Fisheries Institute. pp. 202-225; 241-248.

Baqueiro, C. E. 1998. Patrones en la Dinamica Poblacional y Ciclo Reproductor de Moluscos Bivalvos y Gasteropodos de Importancia Comercial en Mexico, Tesis Doctoral, CINVESTAV, IPN, Unidad Merida, Yuacatan, Mexico. 298 pp.

Baqueiro, C. E., M. Medina & H. Ramirez. 1999. Conch fishery of Campeche. Proc. Gulf and Caribb. Fish. Inst. 45:982-993.

Berg, J. C. & N. L. Adams. 1984. Microwave fixation of marine invertebrates. J. Exp. Mar. Biol. Ecol. 74:195-199.

Bradshaw-Hawkins, V. I. 1982. Contributions to the natural history of the West Indian fighting conch, Strombus pugilis Linnaeus 1758, with emphasis on reproduction. M. Sc. Thesis, McGill Univ. Montreal, Canada. 131 pp.

Defeo, O. 1996. Recruitment variability in sandy beach macroinfauna: much to learn yet. Rev. Chil. Hist. Nat. 69:615-630.

Luna, L. G. 1968. Manual of histologic staining methods of the Armed Forces Institute of Pathology. New York: McGraw-Hill. 253 pp.

Navarrete, J. A., C. Garcia, N. E. Gonzalez. & E. Baqueiro C. 2000. Biologia y ecologia de los gasteropodos del Golfo de Mexico y Mar Caribe. En: D. Flores, ed. Recursos relevantes del Golfo de Mexico y Caribe EPOMEX, Univ. Auton. Campeche, Mexico. pp. 35-52.

Reed, S. E. 1995a. Reproductive anatomy and Biology of the Genus Strombus in the Caribbean: I Males. J. Shellfish Res. 14(2):325-330.

Reed, S. E. 1995b. Reproductive Anatomy and Biology of the Genus Strombus in the Caribbean: II Females. J. Shellfish Res. 14(2):331-336.

Rice, J. & P. Peckerik. 1992. Stock and recruitment. J. Fish. Res. Board. Can. 11:559-623.

Webber, H. H. 1977. Gastropoda: prosobranchia. En: C. G. Giese, y J. S. Pearse, eds. Reproduccion of marine Invertebraytes. Vol. 4. Molluscs, Gastropods and cephalopods. Londres, UK: Academic Press. pp. 1-97.

Young, P. C. 1991. Stock recruitment relationship in scallops: do the Bass strait scallop populations self-recruit? Proc. Bull. Rural Resour. (Australia) 16:110-114.

ERICK BAQUEIRO CARDENAS, (1) * DALILA ALDANA ARANDA (2) AND GISELA MARTINEZ OLIVARES (3)

(1) CICATA, IPN Km. 14.5 Carr. Tampico, Puerto Industrial Altamira, Altamira, Tamaulipas, C.P. 89600, Mexico; (2) Cinvestav Unidad Merida KM. 6 Antigua Carretera a Progreso, Merida, Yucatan, Mexico; (3) Halifax University, Nova Scotia, Canada

* Corresponding author: [e-mail]

TABLE 1.
Maximum, minimum and mean length, and weight of Strombus
pugilis whole, shell and soft parts.

                                                    Soft
                       Shell    Total    Shell     Tissue
                       Length   Weight   Weight   Weight,
Females                 (mm)     (g)      (g)       (g)

  Max.                   86     95.03    80.03     17.34
  Min.                   65     42.05    32.47      6.88
  Mean                   76     61.50    50.10     10.60
Masculinized females
  Max.                   91     90.67    75.69     16.08
  Min.                   82     73.07    63.11      9.93
  Mean                   87     84.50    71.10     13.30
Males
  Max.                   87     96.08    75.81     16.20
  Min.                   63     32.47    25.39      6.99
  Mean                   76     60.50    48.60     10.60

TABLE 2.
Sex percentage and masculinized females of
Strombus pugilis from Campeche, Mexico.

                                   Masculinized
Month            Males   Females     Females

February, 1997    35       60           5
March             34       66
April              0       100
May              36.84    63.16
June             35.29    64.71
July             28.57    71.43
August           47.37    52.63
September        26.32    57.89       15.79
  Mean           26.85    66.97        2.6