Reproduction of the fish Poeciliopsis gracilis (Cyprinodontiformes: Poeciliidae) in Coatetelco, a tropical shallow lake in Mexico José Luis Gómez-Márquez1, Bertha Peña-Mendoza1, Isaías H. Salgado-Ugarte2, Abby K. Sánchez-Herrera1 & Leonardo Sastré-Baez1 1. Laboratorio de Limnología, F.E.S. Zaragoza, U.N.A.M. Batalla 5 de Mayo esq. Fuerte de Loreto, Ejército de Oriente, C.P. 09230 Iztapalapa, México, D.F.; [email protected] 2. Laboratorio de Biometría y Biología Pesquera, F.E.S. Zaragoza, U.N.A.M. Batalla 5 de Mayo esq. Fuerte de Loreto, Ejército de Oriente, C.P. 09230 Iztapalapa, México, D.F.; [email protected] Received 19-VI-2007. Corrected 21-V-2008. Accepted 31-VII-2008. Abstract: A reproductive analysis of 1 225 specimens of Poeciliopsis gracilis obtained through monthly samples from Coatetelco, a tropical shallow lake in Central Mexico, was made. There was an evident sexual dimorphism, including a difference in body size at the onset of reproduction. Sex ratio deviated significantly from unity. Monthly variations in gonadosomatic (GSI), hepatosomatic (HSI) indexes and ovarian development stages showed that the spawning season was from July to October, coinciding with the rainy season and phyto- plankton biomass increase. The largest sizes were 50 mm for females and 43 mm for males. Rev. Biol. Trop. 56 (4): 1801-1812. Epub 2008 December 12. Key words: chloropyll “a”, gonadosomatic index, hepatosomatic index, Poeciliopsis gracilis, reproduction, sex ratio, Mexico. The members of the fish order Nicaragua Lake (Miller 1966, Miller et al. Cyprinodontiformes are cosmopolitan in 2005). P. gracilis has been recently recorded to tropical and temperate latitudes. The genus the North of its previously known distribution Poeciliopsis belongs to the Heterandrini Tribe zone at the Balsas River basin in Morelos and and comprise 44 species. The poeciliids are Puebla, Mexico (Mejia 1992). small fishes, none attains an overall length of Poeciliids live in a broad array of habitats, 50 mm and most are less than half of that size occupying temperate to tropical zones, desert, (Rosen and Bailey 1963, Rauchenberger 1989, rivers, lakes springs, fresh and brackish marsh- Huidobro 2000). Only a small proportion of the es, seacoasts, and saline mangrove swamps. nearly 200 poeciliids species has been studied However, basic ecology of most poeciliids is in an ecological context (Meffe and Snelson unknown. Considering the economic impor- 1989). The porthole livebearer Poeciliopsis tance of poeciliids (aquarium trade, biological gracilis (Heckel 1848) is of Central American control, conservation) few species have been origin (Meffe 1989, Miller et al. 2005). studied in the field as P. gracilis (Huidobro The species is a member of the live-bear- 2000) and P. infans (Galindo-Villegas and ing teleost poeciliids and can be found in the Sosa-Lima 2002); the majority of the available Pacific slope from the Río Verde in Mexico, information comes from laboratory studies to the Eastern tributaries of the Fonseca Gulf (Meffe and Snelson 1989). in Honduras (Choluteca River) and, possibly Martínez et al. (2004) and Maya et al. Nicaragua. On the Atlantic slope it is found (2006) mentioned that ornamental fish culture from the Coatzacoalcos River in Mexico to is one of the main economic activities at the Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 56 (4): 1801-1812, December 2008 1801 Morelos State, being the Poeciliidae family between 24°C and 26°C. The highest air tem- the most cultivated at the fish farms, with an peratures were recorded in May (32°C) and the annual production of 16.5 millions of fry that lowest in December and January (20 - 21°C). represent US$2.59 millions. The observed water temperature fluctuation P. gracilis is a species which is caught at in this study was similar to that reported by several aquatic systems in Mexico. It’s ecologi- Granados (1990), in that low temperatures pre- cally very tolerant, inhabiting in quiet water vailed in January and February, whereas high of streams, flood-water ponds, lagoons, micro temperatures prevailed during the rest of the reservoirs, lakes and dams, in water clear to year. Water level decreased between January turbid or very muddy (Meffe and Snelson Jr. and September. 1989, Miller et al. 2005). This species starts to be reared in laboratory in order to obtain Monitoring: The samples were taken results about to how the environmental con- approximately at monthly periods from May dition affects its survival and how the food 2002 to April 2003. Fish were caught with a amount and quality, affects its growth rate and seine 10 m long and 1.0 m deep, with 5 mm fecundity. mesh and fixed in 10 percent formaldehyde. In spite of the high demand of P. gracilis Specimens were then transported to the labora- as a forage species in Mexico, its commercial tory where they were measured to the nearest value is very low, as from the ecological point 0.1 cm and weighed to the nearest 0.01 g. of view there are few investigations about Maturation stages for females were established the impact that this introduced species causes by gonadal inspection following Mendoza’s on the native fauna and habitats in different technique (1962) and Contreras-MacBeath countries. and Ramírez-Espinoza (1996) description. The To date, no studies in relation with P. ovaries were removed, weighed and the ovules, gracilis reproduction has been carried out at eggs and embryos from each female caught Coatetelco, a tropical shallow lake at Morelos, throughout the study were counted. Mexico. The purpose of this study was to ana- The gonadosomatic and hepatosomatic lyze the relationships between the reproductive indexes (GSI and HSI respectively) were esti- cycle (fecundity-length, fertility-length, size of mated by: first reproduction, sex ratio, maturity develop- ment stages, etc.) of P gracilis and the environ- Wg Wg mental conditions. GSI = 100 We We MATERIALS AND METHODS Wh HSI = Wh 100 Lake Coatetelco (18°45’ N; HSI = 100 Study site: We 99°20’ W) is located at an altitude of 1100 m in e Morelos State (Anonymous 1981, Anonymous 5 Wt 1998). It has a surface area of approximately where W is gonadK = wet10 5 weightWt (g), W is liver g K =10 3 h Lt 3 120 ha, a mean depth of 0.49 m and a maxi- wet weight and, We is evisceratedLt wet weight mum depth of 1.5 m. Gómez-Márquez (2002) (g). This can be considered as a measurement cited that the conductivity varies between of reproductive cost. To establish the size of 574 and 1 110 µsiems/cm, pH values were first reproduction for females, the ovaries were considered as lightly alkaline (8.9 average), examined following the criteria employed by even that at a global way the tendency was Reznick and Miles (1989) and using the logis- to increase from June to December. Lake tic equation (King 1995). For males, we con- Coatetelco is characterized by a sub humid sidered the smallest sample with completely warm climate, with annual mean temperature formed gonopodial structures. 1802 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 56 (4): 1801-1812, December 2008 The total length (Lt)-total weight (Wt) rela- to 0.72 g (males) and 0.1 to 5.0 g (females). tionship was calculates by regression between The females were larger than males (t-student these variables for each sex using the formula: = 13.98; p<0.05). There was an evident sexual dimorphism in the morphological features of P. Wt = aLt b gracilis, being the modification of the anal fin in males to form a gonopodium the main sexual A covariance analysisWg made it possible to distinctive characteristic. determine whetherGSI or= not there100 were significant W differences at p<0.05, fore the length-weight Sex ratio: Of the 1 143 adults specimens relationship between both sexes. dissected, 345 (30.2%) were males and 798 W Condition (K)HSI was= calculatedh 100 for males and (69.8%) were females. The sex ratio of the females using the Fulton’s formula (Nikolsky catch as a whole was 2.3:1 (female:male), sig- We 1963): nificantly different from a 1:1 ratio (χ²= 89.76, p<0.05). The females dominated significantly Wt K =105 throughout the year, except February when Lt3 more adult specimens were males (Fig. 1). Where Wt = total wet weight (g) and Lt = total Length-weight relationship: This rela- length (mm). The Kruskal-Wallis test (p<0.05) tion was evaluated for all individuals, and for was used to test whether condition differed each sex separately (females and males), due to between males and females. the significant difference between the male and Fecundity was estimated by calculating the female slopes of Wt-Lt regressions (ANCOVA; regression of the ovules number on the total F = 19.03, p<0.05). These equations are given length, using logarithms. The sex ratio was below: analyzed for the whole population by month. The statistical significance of the monthly ratio Females: results was established by a goodness of fit Wt = 0.0134 Lt 2.94, R² = 0.9431, p<0.05 Chi-squared test (χ²). Some environmental factors were also Males: investigated to determinate if they are associ- Wt = 0.0155 Lt 2.73, R² = 0.7426, p<0.05 ated with the breeding cycle of the fish. Surface temperature was measured using a thermom- All fishes: eter around 12:00 h during each sampling occa- Wt = 0.0132 Lt 2.94, R² = 0.9319, p<0.05 sion. In addition, previously measured month water temperature data for the period between Weight increased allometrically with size 2002 and 2003 were considered.