Reproductive biology of Menidia jordani (Atheriniformes: Atherinopsidae) in Xochimilco Lake, Mexico Yolanda Mónica Olvera-Blanco,* José Luis Gómez-Márquez,** Bertha Peña-Mendoza,** Ma. Teresa Gaspar-Dillanes*** and Carlos Pérez*** The reproductive biology of Menidia jordani (Woolman, 1894), a native fish of Mexico and one of the most important commercial fish species in Central Mexico for centuries, was analyzed. A monthly sampling bet- ween April 1995 and March 1996 was carried out. Sex ratio was 1.5:1 (female:male), determined by simple observation. Females were larger than males, the largest sizes being 7.2 cm for females and 6.3 cm for males. Standard length at first maturity was 4.8 cm for females and 5.5 cm for males. Monthly variations in gonadosomatic index (GSI), hepatosomatic index (HIS) and ovarian development stages showed that the spawning season occurred mainly from January to May. Best correlation values were between fecundity and length (r = 0.7383; p = 0.0003), compared to those found between fecundity and weight (r = 0.6132; p = 0.002). Fecundity ranged from 143 to 952 eggs per female; mean fecundity was 324 eggs. Key words: Mesa silverside, gonadosomatic index, gonadic maturity, sex ratio. Biología reproductiva de Menidia jordani (Atheriniformes: Atherinopsidae) en el Lago de Xochimilco, México Se analizó la biología reproductiva de Menidia jordani (Woolman, 1894), pez nativo de México, que por varios siglos ha sido una de las especies de peces comercialmente más importantes en el centro de México. Los muestreos se realizaron mensualmente de abril 1995 a marzo 1996. El sexo de los peces fue determi- nado macroscópicamente y la proporción de machos fue significativamente más baja que la de hembras, 1.5:1 (hembra:macho). Las hembras alcanzaron tallas más grandes (longitud patrón) que los machos, la mayor en hembras fue de 7.2 cm y 6.3 mm en machos. La primera madurez fue de 4.8 mm de longitud patrón en hembras y de 5.5 mm en machos. La variación mensual de los índices gonadosomático (IGS) y hepatosomático (IHS) y el desarrollo del ovario mostraron que el desove se realiza predominantemente de enero a mayo. El valor de correlación fecundidad-longitud fue más alto (r = 0.7383; p = 0.0003) que para fecundidad-peso (r = 0.6132; p = 0.002). La fecundidad varió de 143 a 952 huevos por hembra con una media de 324 huevos. Palabras clave: Charal, índice gonadosomático, madurez gonadal, proporción de sexos. Introduction is the genus Chirostoma, which belongs to the subfamily Menidiinae (Chernoff, 1986), with 18 Geographic distribution of Atherinopsidae ran- extant and one extinct species (Barbour, 1973a). ges from the tropics to temperate areas. Nelson The genus Chirostoma is divided into two (1994) found that most members of this family groups: Jordani and Arge. Jordani group contains concentrate in marine shoreline areas; about 50 all of the relatively large species known in Mexi- species are found in freshwater, among them co as “white fish”, while the smaller species be- long to the Arge group, known as “charales” or silverside. All members of the genus are endemic to central Mexico and live in freshwater, but they * Dirección General de Investigación en Acuacultura. Instituto Nacional de Pesca. Pitágoras núm. 1320, Col. Santa Cruz Atoyac, Benito Juárez, México, DF. 03310. *** Dirección General de Investigación Pesquera en el Pací- [email protected] fico Norte. Instituto Nacional de Pesca. Pitágoras núm. ** FES Zaragoza, UNAM. Batalla 5 de Mayo esq. Fuerte de Lore- 1320, Col. Santa Cruz Atoyac, Deleg. Benito Juárez, Méxi- to, Col. Ejército de Oriente, CP 09230 Iztapalapa, México, DF. co, DF. 03310. [email protected]; [email protected]; [email protected] [email protected] Vol. 17, núm. 2, noviembre de 2009 Ciencia Pesquera 65 Y. M. Olvera-Blanco, J. L. Gómez-Márquez, B. Peña-Mendoza, Ma. T. Gaspar-Dillanes and C. Pérez share many features with marine Atherinopsids To understand the reproductive biology of because of their common ancestry (Barbour, M. jordani, the variation of gonadic maturity 1973a; Miller et al., 2005). Reports on their sys- stage, sex ratio, weight-length relationship, first tematics, biology, distribution and ecology have reproductive size and reproductive season were been carried out by Álvarez del Villar (1970) and determined on a yearly basis. Barbour (1973b). Recently Miller et al. (2005) placed all silversides of Mesa Central in the ge- nus Menidia Bonaparte, a classification that is Materials and methods adopted in this study for Menidia jordani. “Charales” are a group of species of econo- Xochimilco Lake (19° 17’ 28’’ and 19° 15’ 58’’ N; mic, social, cultural and ecological importance 99° 04’ 05’’ and 99° 06’ 54’’ W) is located at 2 274 in central region of Mexico, mainly in Pátzcuaro m altitude in Mexico City (INEGI, 2000) (Fig. 1). and Chapala lakes and commonly called “white It has a surface area of approximately 24 km², fish” (M. estor, before Chirostoma estor), along up to 10 m in depth and a mean of 2 m. Sam- with several other silversides such as M. jordani ples were performed monthly from April 1995 to (previously Ch. jordani Woolman (1894)); (Álva- March 1996. rez del Villar, 1970; Miller et al., 2005). Fish were captured with a 30 m length seine The mesa silverside fish or “charal” Menidia with a 0.01 m mesh size. All fish were measured for jordani, inhabits clear, turbid or muddy and quiet total length (TL) and standard length (SL) to the waters of lakes, rivers, ponds, canals, and reser- nearest 1 mm, weighed (total weight TW) to the voirs up to 1 m depths (Miller et al., 2005). They nearest 0.1 g and dissected to determine sex. Go- feed on zooplankton, insects, small fishes and nadic maturity stage was categorized according sometimes snails. Some species of Chirostoma and to Nikolsky (1963). Odontesthes are economically relevant, either for Gonads and liver were removed and weighed sport fishing, artisanal fisheries or aquaculture. to the nearest 0.01 g. Each month, sex ratio was While Menidia jordani is a very important determined for the entire sample. Mean length fishery resource, it is currently in danger due to at first reproduction was established according environmental changes in Xochimilco Lake, and to King (1995), based on the length at which 50% because of its high value and demand in regional (Lm) of all individuals were sexually mature. markets, providing an incentive for local fishers A covariance analysis was conducted to de- to capture small juveniles and adults in an indis- termine whether or not there were significant criminate way. differences at p<0.05 for the length-weight rela- Various aspects of the biology of commercially tionship between both sexes. The standard length important “charales” have been studied by De (SL)-total body weight (TW) relationship was cal- Buen (1945), Barbour (1973a; 1973b), Gallar- culated by a power regression between these va- do (1977), Navarrete (1981), Gómez and Ramí- riables for each sex using the formula: rez de Arellano (1982), Burali (1989), Cházaro (1989), Rodríguez (1989), Peralta (1991), Her- TW = aSLb Eq. 1 nández (1993), Islas et al. (19951), Jiménez and Gracia (1995), Cárdenas and Barrera (1998), where TW is the body weight, SL the standard Soria-Barreto and Paulo-Maya (2005), Martí- length, b the growth exponent or length-weigh nez-Palacios et al. (2006), Rojas-Carrillo (2006), factor, and a is a constant. The values of a and b and Ibáñez et al. (2008). were estimated by means of a linearized form of that equation by taking (base 10) logarithms on both sides and estimating the values of log (a) and log (b) by means of a linear regression, using 1. ISLAS, Y. J., F. Arana y R. Pérez. 1995. Estudio preliminar sobre la reproducción en cautiverio de Chirostoma jordani ordinary least-squares regression. Student’s t-test Woolman (Pisces: Atherinidae) de la zona lacustre de Xochi- was used to the hypothesis of isometric growth milco, D. F. Segundo Seminario Internacional de Investiga- ción de Xochimilco. Asociación Internacional de Investiga- (Ricker, 1975; Pauly, 1984). dores de Xochimilco A.C., pp: 342-345. 66 Ciencia Pesquera Vol. 17, núm. 2, noviembre de 2009 Reproductive aspects of Menidia jordani Fig. 1. Xochimilco Lake, Mexico, showing study site. Gonadosomatic index (GSI) was calculated for from 2.9 to 6.3 cm and 0.32 to 3.18 g for males, each individual based on the relationship bet- and from 4.0 to 7.2 cm and 0.73 to 5.37 g for fe- ween gonad weight (GW) and total body weight males. Females were larger than males (t-value (W), expressed as a percentage (Vlaming et al., = 11.39; p<0.05) (Fig. 2). 1982). Hepatosomatic index (HSI) was calcula- ted for females based on the relationship of liver weight (LW) and (W), expressed as a percentage. Each month, values of gonad stage frequency and mean values of GSI and HSI were plotted to graphically visualize the reproductive cycle and breeding season of the fish. For an estimate of fecundity, ripe females (n = 294) were used, taking the total number of eggs contained in the gonads (Laevastu, 1971; Bagenal, 1978). The variation of fecundity with fish body length was estimated (Bagenal, 1978). Mean fecundity values were calculated according to Shoesmith (1990). Environmental factors were considered in the analysis to determine if there is a relations- hip to the fishes’ breeding cycle. Surface tempe- rature was recorded at 10:00 h during each sam- Fig. 2. Length frequency distribution by sex for Menidia jordani pling event. Previous water temperature data at Xochimilco Lake, Mexico. from 1995 and 1996 were incorporated for the analysis.