Biodiversity, distributions and isolation of microplastics pollution in finfish species in the Panjkora River at Lower and Upper Dir districts of Khyber Pakhtunkhwa province of Pakistan / Biodiversidade, distribuição e isolamento de poluições por microplásticos em espécies de peixes no rio Panjkora nos distritos de Lower e Upper Dir da província de Khyber Pakhtunkhwa do Paquistão

The basic aim of this study was aimed to determine the ichthyofaunal diversity of River Panjkora in both upper and lower Dir districts in Khyber Pakhtunkhwa province of Pakistan.Fish samples were collected by using fishnets from March to September 2020. A total of 724 specimens were collected and classified into 5 families, 14 genera, and 18 species. The overall results revealed that most fish fauna of river Panjkora contains 8 species of family Cyprinidae (56.49%) followed by 4 species of Nemacheilidae (24.44%), 2 species of Channidae (10.63%), and Sisoridae (7.04%), and 1 species of Mastacembelidae (1.38%), respectively. Among all kinds of fish species, Schizothorax plagiostomus (16.57%) was highly dominated and followed by Carassius auratus (11.87%) and Racoma labiata (9.66%) and were reported as highly abundant, especially during April, May, and June. The least abundant species were Glyptothorax punjabensis, Glyptothorax sufii, and Mastacembelus armatus, that constituting 2.48%, 2.20%, and 1.38% of the total fish samples. The Overall Simpson's diversity (1-D= 0.919) and Simpson's Reciprocal index values (1/D= 12.3876), and Shannon's index (H= 2.68) were indicating that river Panjkora contains a quite rich and diverse group of fish species. The highest microplastics observed in site 7 compared to other study area. Conservation steps should be taken as a top priority to protect and conserve the marine environment and natural heritage from further loss, extinction and stop or minimize losses incurred through irresponsible fishery practices

O objetivo básico deste estudo foi determinar a diversidade ictiofaunística do rio Panjkora nos distritos de Lower e Upper de Dir, na província de Khyber Pakhtunkhwa, no Paquistão. Amostras de peixes foram coletadas com redes de arrasto de março a setembro de 2020. Foram coletados 724 espécimes, classificados em 5 famílias, 14 gêneros e 18 espécies. Os resultados gerais revelaram que a maioria da ictiofauna do rio Panjkora contém 8 espécies da família Cyprinidae (56,49%), seguidas por 4 espécies de Nemacheilidae (24,44%), 2 espécies de Channidae (10,63%) e Sisoridae (7,04%) e 1 espécie de Mastacembelidae (1,38%). Entre todas as espécies de peixes, Schizothorax plagiostomus (16,57%) foi altamente predominante, seguida por Carassius auratus (11,87%) e Racoma labiata (9,66%), e elas foram relatadas como altamente abundantes, especialmente nos meses de abril, maio e junho. As espécies menos abundantes foram Glyptothorax punjabensis, Glyptothorax sufii e Mastacembelus armatus, que constituíram 2,48%, 2,20% e 1,38%, respectivamente, do total de peixes amostrados. O índice de diversidade de Simpson (1-D = 0,919), o índice recíproco de Simpson (1/D = 12,3876) e o índice de Shannon (H = 2,68) indicaram que o rio Panjkora contém um grupo bastante rico e diversificado de espécies de peixes. Os microplásticos mais altos foram observados no local 7 em comparação com outra área de estudo. Medidas de conservação devem ser tomadas como prioridade máxima para proteger e conservar o ambiente marinho e o patrimônio natural de novas perdas e extinção e para parar ou minimizar as perdas ocorridas por práticas de pesca irresponsáveis.

Biodiversity, distributions and isolation of microplastics pollution in finfish species in the Panjkora River at Lower and Upper Dir districts of Khyber Pakhtunkhwa province of Pakistan

Abstract The basic aim of this study was aimed to determine the ichthyofaunal diversity of River Panjkora in both upper and lower Dir districts in Khyber Pakhtunkhwa province of Pakistan.Fish samples were collected by using fishnets from March to September 2020. A total of 724 specimens were collected and classified into 5 families, 14 genera, and 18 species. The overall results revealed that most fish fauna of river Panjkora contains 8 species of family Cyprinidae (56.49%) followed by 4 species of Nemacheilidae (24.44%), 2 species of Channidae (10.63%), and Sisoridae (7.04%), and 1 species of Mastacembelidae (1.38%), respectively. Among all kinds of fish species, Schizothorax plagiostomus (16.57%) was highly dominated and followed by Carassius auratus (11.87%) and Racoma labiata (9.66%) and were reported as highly abundant, especially during April, May, and June. The least abundant species were Glyptothorax punjabensis, Glyptothorax sufii, and Mastacembelus armatus, that constituting 2.48%, 2.20%, and 1.38% of the total fish samples. The Overall Simpsons diversity (1-D= 0.919) and Simpsons Reciprocal index values (1/D= 12.3876), and Shannons index (H= 2.68) were indicating that river Panjkora contains a quite rich and diverse group of fish species. The highest microplastics observed in site 7 compared to other study area. Conservation steps should be taken as a top priority to protect and conserve the marine environment and natural heritage from further loss, extinction and stop or minimize losses incurred through irresponsible fishery practices

Resumo O objetivo básico deste estudo foi determinar a diversidade ictiofaunística do rio Panjkora nos distritos de Lower e Upper de Dir, na província de Khyber Pakhtunkhwa, no Paquistão. Amostras de peixes foram coletadas com redes de arrasto de março a setembro de 2020. Foram coletados 724 espécimes, classificados em 5 famílias, 14 gêneros e 18 espécies. Os resultados gerais revelaram que a maioria da ictiofauna do rio Panjkora contém 8 espécies da família Cyprinidae (56,49%), seguidas por 4 espécies de Nemacheilidae (24,44%), 2 espécies de Channidae (10,63%) e Sisoridae (7,04%) e 1 espécie de Mastacembelidae (1,38%). Entre todas as espécies de peixes, Schizothorax plagiostomus (16,57%) foi altamente predominante, seguida por Carassius auratus (11,87%) e Racoma labiata (9,66%), e elas foram relatadas como altamente abundantes, especialmente nos meses de abril, maio e junho. As espécies menos abundantes foram Glyptothorax punjabensis, Glyptothorax sufii e Mastacembelus armatus, que constituíram 2,48%, 2,20% e 1,38%, respectivamente, do total de peixes amostrados. O índice de diversidade de Simpson (1-D = 0,919), o índice recíproco de Simpson (1/D = 12,3876) e o índice de Shannon (H = 2,68) indicaram que o rio Panjkora contém um grupo bastante rico e diversificado de espécies de peixes. Os microplásticos mais altos foram observados no local 7 em comparação com outra área de estudo. Medidas de conservação devem ser tomadas como prioridade máxima para proteger e conservar o ambiente marinho e o patrimônio natural de novas perdas e extinção e para parar ou minimizar as perdas ocorridas por práticas de pesca irresponsáveis.

Correlation of Limnological Features with Ichthyofauna in Hatnur Reservoir in Jalgaon, Maharashtra, India

Background: Limnologycovers the study of all inland waters including running and standing waters, fresh and saline, natural or man-made reservoirs. Unplanned urbanization, rapid industrialization and indiscriminate use of artificial chemicals lead to heavy and varied pollution in aquatic environments causing to deterioration of Limnological features and depletion of aquatic fauna including fish. Scarcity of research related to limnological features and ichthyofauna diversity in Hatnur reservoir stimulated to undertake the present work. Methods: River Tapi (or Tapti) is arising in Madhya Pradesh and flows westward between two spurs of the Satpuda Rangeacross Maharashtra state, and through Gujarat state to the Gulf of Khambhat. Hatnur reservoir (750 90扙, 210 12扤) formed due to an earth-fill dam on Tapi river near Hatnur village in Jalgaon district of Maharashtra state. Water quality parameters were assessed using standard methods described by APHA and fish diversity was evaluated in the Hatnur reservoir. Results: Seasonal fluctuations in water quality parameters and their relationship with ichthyofauna inhabiting the Hatnur reservoir were assessed. The results obtained in the present study indicated that physicochemical properties of water samples collected from the Hatnur reservoir were within recommended limits of the Bureau of Indian Standards (BIS). Conclusion: It is concluded that water in Dam was less polluted, suitable for agricultural and domestic use and suitable to inhabit the fish diversity. Future studies should focus on under-explored and unexplored areas of the Tapi riverine system in North Maharashtra to comprehensively document the fish diversity.

Protein and Mineral Contents in Some Fish Species Available in the Brahmaputra River of Bangladesh

An experiment was conducted in the laboratory of the Department of Agricultural Chemistry, Bangladesh Agricultural University (BAU), Mymensingh to determine protein and major mineral nutrients (viz. Ca, Mg, Na, K, P, S and Fe) in different available fish species of the Brahmaputra River of Bangladesh. Total 32 fish samples of 15 fish species were collected from three locations of the river during November 2017. The highest amount of Ca (2.00%), Mg (4.17%), Na (0.41%), K (3.24%), P (0.17%), S (0.129%) and Fe (226.9 mg kg−1) were obtained from chela (Salmophasia bacaila), chanda (Chanda nama), chingri (Macrobrachium sp.), shingi (Heteropneustes fossilis), bele (Glossogobius giuris), baim (Macrognathus aculeatus) and mola (Amblypharyngodon mola), respectively and the sequence of the mineral nutrients was K > Mg > Ca > Na > P > S > Fe. The study results revealed that 100% of daily Ca requirement can be replenished by consuming 100 g fish flesh portion of the chela (Salmophasia bacaila)/ chingri (Macrobrachium sp.)/ bele (Glossogobius giuris). Similarly, among the 15 fish species, 11 and 12 species alone can contribute 100% of Mg and K requirement for human by taking 100 g fish flesh, respectively. The maximum content of N (3.88%) was obtained from shingi (Heteropneustes fossilis), while the minimum (2.81%) was recorded from mola (Amblypharyngodon mola). The protein content among the fish samples varied between 17.6-24.3% with a mean value of 21.2%. Finally, the study results concluded that the common fishes available in the Brahmaputra River are a good source of protein and major mineral nutrients, which contributes in nutrition to the local people of the country.

Exotic fish diversity in the river teesta, west bengal, india

A survey was conducted in the river Teesta on the exotic fish species from March 2015 to February 2017. A total of nine exotic fish species were recorded from the river. Highest density was recorded in the monsoon season and lowest was found in winter season. Cyprinidae (56 %) was the dominant family with five species followed by claridae and cichlidae each with two species (22 %). Average abundance index (%) of each species ranged from 0.37 – 1.43 %. Exotic fish species competes with indigenous fish species for food and habitat, spreads different disease and also modify the aquatic habitat. The present scenario is warming for native fishes in near future.

Utilização de enzimas exógenas na nutrição de peixes - Revisão de literatura / Use of exogenous enzyme in fish nutrition - Literature review / Uso de enzimas exógenas en nutrición de peces - Revisión de literatura

As enzimas exógenas são adicionadas nas rações para não ruminantes com o objetivo de remover ou diminuir fatores antinutricionais dos alimentos, aumentar a digestibilidade das rações, reduzir a viscosidade dos alimentos, auxiliar na atividade das enzimas endógenas e atuar em substratos que não são degradados pelas enzimas produzidas pelos peixes. Dessa forma, a presente revisão visa a apresentar as enzimas digestivas em peixes, os bioprocessos para produção de enzimas, alguns resultados obtidos com a adição de enzimas exógenas e a influência do uso de enzimas sobre a qualidade da água de cultivo. Diversos tipos de fungos, bactérias e leveduras podem produzir enzimas, por meio de técnicas de recombinação de DNA e mutações. Os peixes possuem estreita relação com o meio no qual estão inseridos, por isso, alterações nos parâmetros físico-químicos da água podem influenciar o crescimento, peso, saúde e reprodução destes. Dessa forma, o uso de enzimas exógenas na alimentação animal pode contribuir para a diminuição do impacto ambiental causado pela produção animal, pois, atuam aumentando a digestibilidade das rações e de nutrientes poluentes como fósforo e nitrogênio quando as enzimas específicas para estes substratos são adicionadas às rações, como a fitase e protease. O uso da biotecnologia, por meio da utilização de enzimas exógenas ou complexos enzimáticos na nutrição de peixes, melhora o desempenho zootécnico, aumenta a digestibilidade das rações e contribui na redução da excreção de nutrientes no ambiente aquático, interferindo de forma positiva na qualidade da água no sistema de produção.

Exogenous enzymes are added in non-ruminant feed aiming to remove or reduce antinutritional factors in feed, increase digestibility, reduce feed viscosity, assisting the endogenous enzyme activities and act on substrates that are not degraded by enzymes produced by the fish. Therefore, this review aims to present the digestive enzymes in fish, the enzyme production bioprocesses, some results obtained with the addition of exogenous enzymes and the influence of using enzymes in the quality of cultivation water. Various types of fungi, bacteria and yeast can produce enzymes through recombinant DNA techniques and mutations. Fish have close relation with the medium in which they are inserted; therefore, changes in the water physico-chemical parameters can influence their growth, weight, health and reproduction. Therefore, the use of exogenous enzymes in animal nutrition can contribute to reducing the environmental impact of animal production, and thus act by increasing the digestibility of nutrients and pollutants such as phosphorus and nitrogen when specific substrates for these enzymes are added to the feed, such as phytase and protease. The use of biotechnology in the use of exogenous enzymes or enzyme complexes in fish nutrition improves animal performance, increases feed digestibility and contributes to reducing the excretion of nutrients in the aquatic environment, positively interfering in the water quality in the production system.

Las enzimas exógenas son añadidas a las dietas de no rumiantes, con el objetivo de eliminar o reducir factores anti nutricionales de alimentos, aumentar la digestibilidad de los piensos, reducir la viscosidad de los alimentos, ayudar en la actividad de las enzimas endógenas y actuar en sustratos que no se degradan por las enzimas producidas por los peces. Así, esta revisión busca presentar las enzimas digestivas en peces, los bioprocesos para la producción de enzimas, algunos resultados obtenidos con la adición de enzimas exógenas y la influencia del uso de enzimas en la calidad del agua del estanque. Varios tipos de mohos, bacterias y levaduras pueden producir enzimas, mediante técnicas de ADN recombinante y mutaciones. Los peces tienen estrecha relación con el medio ambiente en que viven, por eso, alteraciones en los parámetros físico-químicos del agua pueden influir en el crecimiento, peso, salud y reproducción de estos. Por lo tanto, el uso de enzimas exógenas en la alimentación animal puede contribuir a reducir el impacto ambiental causado por la producción animal, pues, actúan aumentando la digestibilidad de piensos y nutrientes contaminantes como el fósforo y el nitrógeno cuando las enzimas específicas para estos sustratos son añadidas a piensos, como la fitasa y proteasa. El uso de la biotecnología, mediante el uso de enzimas exógenas o complejos de enzimas en la alimentación de peces, mejora el rendimiento zootécnico, incrementa la digestibilidad de pienso y contribuye en la reducción de la excreción de los nutrientes en el medio acuático, interfiriendo positivamente en la calidad del agua en el sistema de producción.

Hematological and morphometric blood value of four cultured species of economically important tropical foodfish

The use and validation of fish health monitoring tools have become increasingly evident due to aquaculture expansion. This study investigated the hematology and blood morphometrics of Piaractus mesopotamicus, Brycon orbignyanus, Oreochromis niloticus and Rhamdia quelen. The fish were kept for 30 days in 300-liter aquariums, after which they were anesthetized with benzocaine and blood was collected from caudal vessels. In comparison to other species, B. orbignyanus presented the highest hematocrit (Ht), RBC averages and Mean Corpuscular Volume (MCV) with a particular range of data. B. orbignyanus presented lower Ht, Hb, RBC averages and values, and Mean Corpuscular Hemoglobin Concentration (MCHC). Oreochromis niloticus presented lower Ht, Hb, RBC averages and values, and Mean Corpuscular Hemoglobin Concentration (MCHC). Rhamdia quelen and O. niloticus presented higher variation of White Blood Cells (WBC), neutrophils (Nf), lymphocytes (Lf), monocytes (Mf) and thrombocytes (Trb). Data of large axes (LA), minor axes (MA), surface (SF) and volume (VL) are in the same variance range. This study has demonstrated that hematological variances can occur between animals of different species as well as of the same species.

O uso e validação de ferramentas para monitorar o estado de saúde dos peixes está se tornando mais evidente, devido à expansão da aquicultura. Este estudo investigou a hematologia e a morfometria do sangue de Piaractus mesopotamicus, Brycon orbignyanus, Oreochromis niloticus e Rhamdia quelen. Os peixes foram mantidos por 30 dias em aquários de 300 litros, após esse período os peixes foram anestesiados com benzocaína e o sangue coletado por punção caudal. Em comparação com outras espécies B. orbignyanus apresentou maiores médias de hematócrito (Ht), eritrócitos (Eri) e volume corpuscular médio (VCM) com um determinado intervalo de dados. Oreochromis niloticus apresentou menor média e valor de Ht, Hb, eritrócitos e concentração de hemoglobina corpuscular média (CHCM). Rhamdia quelen e O. niloticus apresentaram maior variedade de leucócitos (Leu), neutrófilos (Nf), linfócitos (Lf), monócitos (Mf) e de trombócitos (Trb). Dados de eixos maiores (EMA), eixos menores (EME), superfície (SF) e volume (VL) estão no mesmo intervalo de variação. Este estudo demonstrou que as variações hematológicas não ocorrem somente entre os animais de diferentes espécies, mas também entre os indivíduos da mesma espécie.

Bothriocephalus acheilognathi (Cestoda) in the endangered fish Profundulus hildebrandi (Cyprinodontiformes), Mexico

The Asian fish tapeworm, Bothriocephalus acheilognathi, has been considered one of the most dangerous parasites for cultured carp and a risk for native freshwater fish populations worldwide. This cestode is highly pathogenic for fishes especially fry. In this paper we record B. acheilognathi parasitizing the endangered and endemic freshwater fish Profundulus hildebrandi from the endorheic basin of San Cristóbal de las Casas, Chiapas, Mexico. B. acheilognathi was recorded from 10 of the 11 sampled localities, with high values of prevalence (>60%) and mean abundance (>4.50). The infection was persistent all through the year; gravid cestodes were recorded in all samples. It is assumed that B. acheilognathi entered to this area through the introduction of common carp Cyprinus carpio, for aquacultural purposes. The data presented in this paper document the successful introduction, colonization and establishment of this alien species into the endangered P. hildebrandi. Rev. Biol. Trop. 59 (3): 1099-1104. Epub 2011 September 01.

El céstodo Asiático, Bothriocephalus acheilognathi, es considerado como uno de los helmintos más peligrosos para peces de cultivo, y un riesgo potencial para las poblaciones silvestres de peces en todo el mundo. La patología que causa es grave, principalmente en larvas y juveniles de peces. En este trabajo registramos la presencia de B. acheilognathi en el pez endémico de Chiapas y amenazado de extinción, Profundulus hildebrandi, en la cuenca endorreica de San Cristóbal de Las Casas, Chiapas, México. El céstodo B. acheilognathi fue registrado en 10 de las 11 localidades muestreadas, con valores altos de prevalencia (>60%) e intensidad promedio (>4.50). Registramos esta infección durante todo el año, con presencia de céstodos grávidos en todos los meses muestreados. Asumimos que B. acheilognathi ingresó a esta área geográfica con la introducción de la carpa común, Cyprinus carpio, para acuicultura. Los datos que presentamos en este trabajo documentan la introducción exitosa, la colonización y el establecimiento de esta especie exótica de parásito sobre P. hildebrandi, especie dulceacuícola, endémica y amenazada de extinción.

Physical factors and their influence on fish species composition in Asa Lake, Ilorin, Nigeria

The effect of physical factors on fish species composition was studied during 12 months in Asa Lake, Nigeria. Fish and water samples were collected bimonthly (March 2003 to February 2004) in the morning. Fish samples were caught with gill nets set at the surface and bottom habitats. There were 11 fish families and 21 species. Osteoglossidae, Anabantidae, Channidae, Schilbedae and Cyprinidae were rare and occurred seasonally in fishermen catches, while Mormyridae, Cichlidae, Mochokidae, Characidae, Bagridae and Clariidae showed less variation and were more common. Characidae and Cichlidae were the most abundant (23.0 and 18.6% respectively) while Osteoglossidae, Channidae and Anabantidae were the least (1.7, 2.1 and 2.3% respectively). Clariidae and Mormyridae had the highest weight with 16.0% and 12.3% respectively, while Anabantidae had the lowest (3.4%). Surface water temperatures were generally higher than air temperatures during the afternoon, except from January to March when air temperatures were high (28.1 to 28.7 ºC) due to low relative humidity (39 to 70%). In the morning, surface water temperatures (25.5 to 26.3 ºC) became higher than air temperatures (25.2 to 26.0 ºC) from May to December, when relative humidity values were also high (50 to 88%). The differences between surface and bottom water temperatures was generally higher (0.7 to 3.1 ºC; P < 0.05) in the afternoon (0.2 to 0.8 ºC) due to sunlight. Temperature differences in the surface and bottom waters were usually higher during the dry season (P < 0.05), for similar reasons. Captures were higher in the dry season when the fish concentrated in the warmer, steadier and scarcer water. Minimal and maximal temperatures were different for surface and bottom waters (P < 0.05). However, there were no marked variations in temperature patterns or species distribution. Rev. Biol. Trop. 57 (1-2): 167-175. Epub 2009 June 30.

Estudié la composición de especies de peces y las temperaturas durante 12 meses en el lago Asa, Nigeria. Recolecté muestras de peces y de agua bimestralmente en la mañana, de marzo 2003 a febrero 2004. Los peces (11 familias y 21 especies) fueron capturados con atarrayas en la superficie y el fondo. Osteoglossidae, Anabantidae, Channidae, Schilbedae y Cyprinidae fueron raras y aparecieron estacionalmente en las capturas de pescadores, mientras que Mormyridae, Cichlidae, Mochokidae, Characidae, Bagridae y Clariidae mostraron menos variación y fueron más comunes. Las familias Characidae y Cichlidae fueron las más abundantes (23.0 y 18.6% respectivamente) mientras Osteoglossidae, Channidae y Anabantidae fueron las más escasas (1.7, 2.1 y 2.3% respectivamente). Clariidae y Mormyridae tuvieron el peso más alto con 16.0% y 12.3% respectivamente, mientras que Anabantidae fue la más baja, con 3.4%. La estación seca correspondió con capturas altas al concentrarse los peces en el agua más cálida, estable y escasa. Las temperaturas mínimas y máximas fueron diferentes en las aguas superficiales y del fondo (P < 0.05). No obstante, no hubo variaciones marcadas en el patrón de temperatura y distribución de peces.

The fish species composition and variation of catch from the small-scale gillnet fishery before, during and after the 1997-1998 ENSO event, central Mexican Pacific

In the tropical and subtropical coastal zone, were highly diverse fish communities occur, it is important to study the small scale fisheries exploiting these communities. For this study, 219 fishing days were carried out in Bahia de Navidad, Jalisco, Mexico. Four gillnets with different mesh sizes (76.2, 88.9, 101.6 and 114.3 mm) were used for the fishing operations, from April 1994 to March 1995 and from January 1998 to December 2000. A total of 26126 organisms weighting 11680 kg were caught. One hundred and eighty three species belonging to 57 families and 19 orders were identified. Ten species accumulated more than 60% of the total abundance and biomass, the remaining species (173) individually contributed with less than 2% of the total abundance and biomass. The most important species in the catch were Microlepidotus brevipinnis, Caranx caballus, Haemulon flaviguttatum, Scomberomorus sierra, C. caninus, C. sexfjasciatus, Lutjanus guttatus and L. argentiventris. The catch per unit of effort showed a large variation during the study, both in number and biomass. On average, 110 fishes and 48.5 kg fishing day(-1) were caught. The maximum values were recorded during January and October 1998 (250 fishes and 100 kg fishing day(-1)), and the minimum values were recorded during September and November 1994 (25 org. and 10 kg fishing day(-1)). The total abundance and biomass was lower during the 1994-95 period (F=6.16, 8.32, P<0.05). There were statistically significant differences among the annual catch from each gillnet. All the environmental changes caused by the ENSO event had ecological and economic effects that can be rated from moderate to severe.

Se llevaron a cabo 219 días de pesca experimental en la Bahía de Navidad, Jalisco, México. Se utilizaron cuatro redes de enmalle de diferente luz de malla (76.2, 88.9, 101.6 and 114.3 mm de luz de malla), de abril de 1994 a marzo de 1995 y de enero de 1998 a diciembre de 2000. En total se capturaron 26126 organismos que pesaron 11680 kg. Fueron identificadas 183 especies pertenecientes a 57 familias y 19 órdenes. Diez especies acumularon más del 60% de la abundancia y biomasa total, el resto de las especies (173) individualmente aportaron menos del 2% de la abundancia y biomasa total. Las especies más importantes en la captura fueron Microlepidotus brevipinnis, Caranx caballus, Haemulon flaviguttatum, Scomberomorus sierra, C. caninus, C. sexfasciatus, Lutjanus guttatus y L. argentiventris. La captura por unidad de esfuerzo mostró una gran variación durante todo el periodo de estudio, tanto en número de organismos como en biomasa. En promedio se capturaron 110 organismos/día de pesca (48.5 kg/día de pesca). Los valores máximos se registraron durante enero y octubre de 1998 (250 peces y 100 kg por día de pesca), y el mínimo se registró durante septiembre y noviembre de 1994 (25 organismos y 10 kg por día de pesca). La abundancia y biomasa total fue menor durante el periodo 1994-1995 (F=6.16, 8.32, P<0.05). Se encontraron diferencias estadísticamente significativas entre la captura anual de las diferentes redes. Los cambios ambientales provocados por el evento ENOS tuvo efectos que pudieran considerarse de moderados a severos, tanto ecológicos como económicos.

Patterns of fish species richness in rivers of the central region of Argentina

We analyzed the variation of fish species richness and trophic structure along an upstream-downstream gradient and identified the factors associated with the pattern observed. The fish community composition varied along a headwater-downstream gradient. Species richness and trophic structure decreased significantly with increasing altitude and increased with stream order and distance from source. Headwater communities showed a simple structure. Oncorhynchus mykiss was the only fish captured or noticeably dominant at high altitudes. Thus, headwater can be classified as "trout zones". From these zones to downstream areas fish communities changed because of the addition of other fish species. This phenomenon probably occurs because of an increase in habitat diversity.

O presente trabalho teve por objetivo analisar a variação da riqueza de espécies ícticas e da estrutura trófica das comunidades do gradiente nascente-desembocadura, nos rios da região central da Argentina, e identificar os fatores associados ao padrão observado. A composição da comunidade íctica variou desde as cabeceiras até a desembocadura dos sistemas lóticos considerados. A riqueza e a estrutura trófica se relacionaram significativamente com a altitude, a ordem e a distância da origem. As comunidades de cabeceira apresentaram estrutura simples. Oncorhynchus mykiss foi a única espécie capturada ou claramente dominante nas maiores altitudes. Assim, as zonas de nascentes podem ser classificadas como "zonas de trutas". Desde estas zonas até a desembocadura, as comunidades de peixes mudaram devido à adição de novas espécies. Esse fenômeno provavelmente se deve ao incremento da diversidade de habitat e à maior estabilidade ambiental que caracteriza as zonas baixas dos cursos.