Effects of urbanization and environmental heterogeneity on fish assemblages in small streams

The structure of freshwater assemblages may be driven directly by urbanization or indirectly by a reduction in environmental heterogeneity (EH). Disentangling the effects of urbanization and EH requires uncorrelated proxies of each of these factors. We assessed the effects of the degree of urbanization and EH on the structure of fish assemblages. We sampled fish in 45 streams located in the urban area of Cuiabá. We assessed the effects of urbanization and EH on rarefied fish species richness (Srarefied), the local contribution to beta diversity (LCBD), and composition with linear models and distance-based redundancy analysis. Our indexes of urbanization and EH were not correlated. We found that both Srarefied and the LCBD decreased with an increasing degree of urbanization, but were not associated with EH. We also noted that few native fish species abundances were associated with the EH. Serrapinnus microdon, S. calliurus, Hemigrammus tridens, and Astyanax lacustris were abundant in streams with a lower degree of urbanization. The non-native Poecilia reticulata was more abundant in streams with a higher degree of urbanization. Our results highlight that urbanization leads in negative impacts on fish assemblages, such as decreases in diversity and the dominance of non-native species.(AU)

A estrutura de assembleias de água doce pode ser influenciada diretamente pela urbanização ou indiretamente por reduções em heterogeneidade ambiental (HA). Para separar os efeitos da urbanização dos da HA, variáveis substitutas a esses processos precisam ser não-correlacionadas. Avaliamos os efeitos do grau de urbanização e HA na estrutura das assembleias de peixes. Amostramos peixes em 45 riachos localizados na área urbana de Cuiabá. Avaliamos os efeitos da urbanização e HA na riqueza rarefeita de espécies de peixes (Srarefeita), contribuição local para a diversidade beta (LCBD) e composição de espécies utilizando modelos lineares e análise de redundância baseada em distância. Nossos índices de urbanização e HA não foram correlacionados. Observamos que tanto a Srarefeita e a LCBD diminuíram com aumentos no grau de urbanização, mas não foram correlacionadas com a HA. Também observamos que as abundâncias de poucas espécies de peixes nativos correlacionaram-se com HA. Serrapinnus microdon, S. calliurus, Hemigrammus tridens e Astyanax lacustris foram mais abundantes em riachos com menor grau de urbanização. A não-nativa Poecilia reticulata foi mais abundante em riachos com maior grau de urbanização. Nossos resultados destacam que a urbanização resulta em impactos negativos nas assembleias de peixes, tais como reduções da diversidade e a dominância de espécies não-nativas.(AU)

Norethindrone-induced masculinization and progeny testing in guppy, Poecilia reticulata (Peters 1859).

Norethindrone(NE) was evaluated for its efficacy on alteration of sex ratio of P. reticulata. Either the young fry or the brooders and the resultant fry were fed a commercial diet incorporated with NE at 0, 25, 50, 75 and 100 mg kg-1 diet (ppm) for 30-40 d in rectangular glass aquaria; this was followed by 40-60 d rearing on NE-free diet in out-door concrete tanks. In general, the androgen treatment altered sex ratio, leading to the production of a dose dependent increase in the percentage of males. The oral administration of the steroid at 75 ppm for 40 d or 100 ppmfor 30 or 40 d to first feeding fry, yielded 100% males. On the other hand, NE administration to brooders before parturition and the resultant fry also produced an all-male population of guppy. The sex ratio of the untreated control was almost 1:1. The survival of fish in all the trials was high, ranging between 67 and 100%. Mating masculinized males (“XX” male) with normal female resulted in an all-female progeny, while crossing normal male (XY) from treatment groups with normal female sired normal sex ratio (1:1), elucidating XX-XY sex determination system in the guppy.

Reproduction of the fish Poeciliopsis gracilis (Cyprinodontiformes: Poeciliidae) in Coatetelco, a tropical shallow lake in Mexico

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 phytoplankton 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.

Se realizó el análisis reproductivo de 1 225 organismos de Poeciliopsis gracilis que se obtuvieron de manera mensual en el lago Coatetelco, un cuerpo somero tropical en México. Se hizo evidente un dimorfismo sexual en las características morfológicas de esta especie. Se observó una diferencia en el tamaño corporal entre los sexos al inicio de la reproducción. La proporción sexual fue diferente de uno. Con base en la variación mensual del índice gonadosomático (IGS), hepatosomático (IHS) y los estadios de madurez gonádica, se observó que la época de reproducción de P. gracilis se realiza entre julio y octubre, que coincide con la época de lluvias e incremento de la biomasa del fitoplancton. La talla más grande registrada fue de 50 mm para las hembras y de 43 mm para los machos.

Fecundidad, fertilidad e índice gonadosomático de Poecilia reticulata (Pisces: Poeciliidae)en Heredia, Costa Rica / Fertility, fecundity and gonadosomatic index of Poecilia reticulata (Pisces: Poeciliidae) in Heredia, Costa Rica

Entre setiembre y noviembre de 1998 se determinó la fecundidad,fertilidad e índice gonadosomático de Poecilia reticulata (Peters 1859),a partir de especímenes recolectados en un estanque en Santo Domingo de Heredia,Costa Rica.Las hembras presentaron una longitud total promedio de 34.43 ± 7.26 mm con un ámbito entre 17.80 y 51.50 mm y un peso total promedio de 0.69 ± 0.48 g,con un ámbito entre 0.06 y 2.32 g.Se determinó que esta especie presenta superfetación,matrotrofía y se mantuvo sexualmente activa durante todo el período de estudio.La fertilidad se rigió por la ecuación F =0.527e0.1171Lt (r2 =0.9404)y con una fertilidad promedio para la población de 56.1 ± 43.6,con un ámbito entre 7.98 y 197.58 (huevos +embriones).La fecundidad se rigió por la ecuación Fo = 0.695e0.1076 Lt (r2 =0.9376)con una fecundidad promedio para la población de 48.95 ± 35.99, con un ámbito entre 6.98 y 178.99 (ovocitos +óvulos). El índice gonadosomático en hembras se rigió por la ecuación IGS =0.0014e 0.134 Lt (r 2 =0.8581)y se encontró un índice gonadosomático promedio de 0.25 ± 0.27% con un ámbito entre 0.02 y 1.31%

Between September and November of 1998,1 432 females of Poecilia reticulata were collected in a pond in Santo Domingo,Heredia,Costa Rica.The average total length of females was 34.43 ± 7.26 mm (range 17.80 and 51.50 mm)and the average total weight of 0.69 ± 0.48 g (range 0.06 and 2.32 g). This species is a viviparous matrotrofic and the specimens were sexually mature.The total length-fertility relationship was F =0.527e 0.1171Lt (r2 =0.9404).The average fertility was 56.1 ± 43.6 (eggs +embryos)(range 8.0 and 197.6).The total length-fecundity relationship was Fo =0.695e0.1076 Lt (r2 =0.9376).The average fecundity was of 49.0 ± 36.0 (oocytes +ova)(range 7.0 and 179.0).The total length-gonadosomatic index relationship was IGS =0.0014 e0.134 Lt (r2 =0.8581).The average gonadosomatic index was 0.25 ± 0.27%(range 0.02 and 1.31%)

Cultivo de Poecilia reticulata (Pisces: Poecilidae) en cuerpos de agua tropicales, Veracruz, México / Culture of Poecilia reticulata (Pisces: Poecilidae)in tropical water bodies, Veracruz, México

Los peces ornamentales cultivados se han popularizado como mascotas, generando una demanda local que no se ha podido cubrir con la producción de México y por lo tanto deben importarse. Poecilia reticulata "guppy ",es un pez muy popular en el ámbito acuarístico,hoy en día se ha logrado desarrollar una gran cantidad de variedades según su coloración,tipo y forma de cola. Son peces vivíparos que toleran un ámbito extremo de temperatura,siendo la más adecuada entre 25ºC y 28ºC.El tiempo que tardan las hembras en expulsar a las crías una vez que quedan preñadas, oscila entre los 25 y 30 días dependiendo de la temperatura. En esta investigación, el ciclo reproductivo completo se desarrolló en jaulas flotantes, en una laguna tropical situada en la Llanura Costera del Golfo Sur, Veracruz, México. Se diseñó la infraestructura necesaria para producir guppys (P. reticulata) incluyendo el manejo de reproductores,crianza, engorda, alimentación y comercialización,e valuando su factibilidad técnica y financiera. Se realizó un estudio de mercado,a través de una encuesta aplicada a los propietarios de los 22 acuarios existentes en la Ciudad de Veracruz,México. Se analizaron las frecuencias de oferta y demanda de cada especie con respecto a la temporada del año, lugar de origen y resistencia al manejo. Las características hidrobiológicas presentaron valores medios de temperatura (31.4ºC), oxígeno disuelto (4.5 mgl-1) y pH (6.8). Con los datos obtenidos en campo se realizó un modelo para producción de P.reticulata ,obteniendo una relación beneficio/costo=1.16,correspondiente al ingreso mínimo potencial con una ganancia bruta de US$257.67, proporcionando empleo a dos personas El aprovechamiento de cuerpos de agua en regiones tropicales a través de la producción de peces de ornato representa una alternativa para disminuir la presión sobre las poblaciones silvestres y las tierras de cultivo,proporcionar fuentes de empleo e incrementar los ingresos para el...

Poecilia reticulata, also known as guppy, is the most popular fish in the aquarium environment. Guppys are viviparous fish with high tolerance to extreme temperatures.The development of the offspring takes between 25 and 30 days. We developed a technology for raising guppys,which outlines infrastructure and devices for reproduction, nursery, feeding, and commercialization,evaluating the financial and technical feasibility of this technology in a case study. The complete reproductive cycle occured in floating cages with 1 mm mesh and the method was tested in a tropical lagoon in Mexico.Water quality was monitored throughout the study period (temperature, dissolved oxygen and pH levels). A marketing survey was carried out at all existing aquarium shops in Veracruz City. Data collected depict quantities demanded and offered for each species by season,place of origin, and resistance to handling.The hydrobiological characteristics were:average temperature 31.4 ºC, dissolved oxygen 4.5 mgl-1,and pH level 6.8.With these values we built a production function,and used it to evaluate profitability. We estimate a benefit/cost ratio of 1.16,with a net annual income of US$257.67. The system may provide two permanent jobs