Reproduction of Megapitaria Squalida (Bivalvia: Veneridae) in the Southeast Gulf of California, Mexico
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Reproduction of Megapitaria squalida (Bivalvia: Veneridae) in the Southeast Gulf of California, Mexico Ernesto Álvarez-Dagnino, Apolinar Santamaría-Miranda, Manuel García-Ulloa & Andrés M. Góngora-Gómez* Instituto Politécnico Nacional, Centro Interdisciplinario de Investigación para el Desarrollo Integral Regional (CIIDIR-Unidad Sinaloa), Departamento de Acuacultura, Guasave, Sinaloa, México; [email protected], [email protected], [email protected], [email protected]* Received 17-XI-2016. Corrected 20-III-2017. Accepted 19-IV-2017. Abstract: Bivalves reproductive cycle varies according to the particular environmental conditions where they are found, and these reproductive details represent basic information for their capture, management and conser- vation strategies. With this objective, the reproductive cycle of the clam Megapitaria squalida, inhabiting the Southeast of the Gulf of California (Altata Bay, Sinaloa, Mexico), was studied using histology and changes in the number and size of oocytes, from June 2013 to June 2014. Histological analysis of the gonads showed spawning activity throughout the year, with two peaks. The first was registered in October and it was accompanied by the highest decrease of weight; the second was in February with the highest percentage of spawning population; besides, a resting period was observed in December. The sex-ratio (female:male) of the clam population was 1.08:1 (χ2 = 5.72, d.f. = 1, P < 0.05). Mean oocyte size and number were different (P < 0.05) among all sampling months and fluctuated from 34.6 ± 5.8 µm in June 2014, to 41.9 ± 6.8 µm in February 2014, and from 443.8 ± 424.5 in February 2014, to 1 214.4 ± 267.6 counted in April, respectively. With these results we suggest a protec- tion season from October to November, when the most intense release of gametes occur in this population. Rev. Biol. Trop. 65 (3): 881-889. Epub 2017 September 01. Key words: gonadic index, Megapitaria squalida, oocyte development, spawning season, capture man- agement, conservation. Studies on reproduction of commercial particularly appreciated in Mexico, and rep- bivalves are essential to come up with man- resents an important alternative fishery in the agement strategies for their conservation and Gulf of California and the Pacific coast of sustainable exploitation. The clam Megapitaria Mexico. Commonly, clams are captured for squalida (Sowerby, 1835) commonly known as personal consumption or sold in local and “squalid callista” or “callista clam”, is distrib- regional markets. M. squalida is harvested uted from the North of California (Scammon’s by free or scuba diving until a depth of 10 Lagoon) along the Pacific coast, to Mancora, m, and is also hand collected in intertidal Peru, and in both coasts of the Gulf of Cali- sand flats (Scheweers, Wolff, Koch, & Sinsel- fornia. It is a filter-feeder that lives burrowed Duarte, 2006). There are some reports about in sandy sediments, from intertidal areas to its exploitation in Bahia Concepción (Castro- depths of about 160 m (Keen, 1971), and its Ortíz, Tripp-Quezada, & Anguas-Velez, 1992) shell can reach a length, height and width of and different coastal locations of the Gulf 120, 97 and 68 mm, respectively (Singh, Vélez, of California, Mexico (Baqueiro-Cárdenas, & Fajardo, 1991). Masso, & Guajardo, 1982). However, López- Although this species is considered as Rocha et al. (2010) stated that the callista clam a resource of low commercial value, it is fishery in some places of Baja California Sur Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 65 (3): 881-889, September 2017 881 reached its maximum level of exploitation and Gulf of California and to propose management overfishing. Besides, Vázquez-Hurtado, Manz- practices for its sustainable conservation. ano-Sarabia and Ortega-Rubio, (2011) pointed out that anomalous conditions of sea surface MATERIALS AND METHODS temperature have exerted negative effects on clam landings. A total of 210 specimens of M. squalida Latest production statistics in 2014 report were hand collected (N = 30 bimonthly) on a total volume of 4 319 tons of which 99.7 % a sandy bottom (1.5 m depth) in Altata Bay, were registered from Northwest Mexico, and Sinaloa, Mexico (24°20’55” - 24°62’67” N the rest for the state of Sinaloa, in the South- & 107°20’25 - 107°92’36” W), and examined eastern part of the Gulf of California (SAGAR- for histological studies from June 2013 to June PA, 2015). In the specific case of Sinaloa state, 2014. The climate of this region is warm (17.2 the annual average catch of M. squalida was to 32.2 °C, mean minimum and maximum around 53 tons in 2008, with a collapse to 12 temperatures; Ruíz, Medina, Macías, Silva, & tons in 2014; that pointed out an overexploita- Díaz, 2005), with a rainy season from June tion of this resource. Since official estimations to September-October, and a dry season from for last two decades refer to captures all year November to May (Gaxiola-Castro, 2003). round in this state, it is possible to assume a lack of a close season, as a consequence of the Environmental parameters: To evaluate absence of biological studies on its reproduc- the possible influence of environmental factors tive cycle. The overexploitation of the cal- on the reproductive cycle of M. squalida, water lista clam has led to regional fishery authorities parameters were measured at each sampling. (ISAPESCA, Instituto Sinaloense de Acuacul- Seawater temperature (ºC) and salinity were tura y Pesca) to impel a research project on dif- monitored with an oxymeter and a refractome- ferent biological aspects of the species. Part of ter, respectively. Water samples were collected this project was focused to increase knowledge from the bottom (0.90 m deep) for determina- on this species reproductive cycle, for a better tion of chlorophyll a (Cla). Pigment analyses management and conservation of this clam in were carried out after water filtration with Sinaloa state (Ruíz-García et al., 2013). Whatman GF/F glass filters (0.7 µm pore size) Nowadays, the reproductive cycle of the using Millipore vacuum filtration. The Cla callista clam has been described predominantly concentration (mg/m3) was determined by stan- for the populations from Northwestern Mexico dard spectrophotometric methods (Strickland (Baqueiro & Stuardo, 1977; Villalejo-Fuerte, & Parsons, 1972). Concentrations of Cla were García-Melgar, Ochoa-Báez, & García-Gasca, calculated using the thrichromatic equations of 1996; Quiñones-Arreola, 2003; Arellano-Mar- Jeffrey and Humphrey (1975). tínez, Quiñones-Arreola, Ceballos-Vázquez, & Villalejo-Fuerte, 2006; Schweers et al., 2006), Biometric analysis: The shell length but there is no information for the Southeast- (SL = line straight distance from umbo to ven- ern clam communities of the Gulf of Califor- tral margin of the shell, mm) and weight (g) of nia. The reproductive cycle of bivalves varies each clam were measured in situ with a caliper with the geographic location, according to the (0.01 mm) and a portable balance (0.0 g), particular environmental conditions in each respectively. The changes in weight could be location, mainly water temperature and food related to somatic growth and/or variations in availability (Cruz & Villalobos, 1993; Rodrí- the size of the specimens between successive guez et al., 1993; Vázquez-Hurtado et al., samples. Thus, the variations of weight was 2011). Therefore, the aim of this study was to estimated for a standard individual of 67.95 provide information on the reproductive cycle mm long, the mean size of the population, for of M. squalida in the Southeast coast of the which the changes in weight must be related 882 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 65 (3): 881-889, September 2017 with the development of the gonads. For the that this structure is located at the cell center estimation of the bimonthly weights of the (Laruelle, Guillou, & Paulet, 1994). standard individual, regression lines for the One-way ANOVA was employed to exam- weight-length relationship were calculated, ine the sizes and weights of female and male after a logarithmic transformation of Ricker´s M. squalida at each sampling; when statisti- function W = aLb (Ricker, 1975), where W cal significances were detected, a posteriori is the weight, L the length, a the ordinate at multiple comparison tests (Tukey´s test) were origin and b the slope. The gonadic index was conducted. One-way ANOVA was also used to obtained according to the stages 1 = undif- evaluate the variations in number and diameter ferentiated and resting, 2 = development, and of oocytes. A Pearson’s correlation analysis 3 = ripe, and applying the formula GI = (n1 + was applied to investigate the relationship 3n2 + 2n3)/Nt, where n = number of organisms among the mean oocyte diameter, water tem- in stages 1, 2 and 3, and Nt = total organisms perature, Cla concentrations and growth (SH, (Arellano-Martínez et al., 2006). mm; TW, g) of the callista clam. The differ- ences in bimonthly sex ratios were tested using Histological preparations: To determine Chi-square tests (χ2) with Yates’ continuity the gonad development, the visceral mass of correction (Zar, 1996). All statistical analyses each clam (gonad included) was dissected and were performed using STATISTICA for Win- fixed in Davison’s solution for 24 hours. A dows (ver. 6.0, Statsoft). A significance level of conventional histological technique (Huma- α = 0.05 was set in all tests. son, 1979) comprising dehydration through a sequence of alcohol solutions of increasing RESULTS concentration followed by clearing with Hemo- De® and embedding in Paraplast-Xtra® was Environmental parameters: The maxi- used. Sections of tissue that were 4 µm thick mum seawater temperatures at the collecting were cut, stained with haematoxylin-eosin and site were registered in June and August (31.0 examined under a light microscope. Each clam ± 0.0 °C) and the minimum (20.0 ± 0.8 °C) in was analyzed for gonadal development, from December, January and February.