Occurrence and toxicity of Microcystis aeruginosa (Cyanobacteria) in the Paraná River, downstream of the Yacyretá dam (Argentina) / Presencia y toxicidad de Microcystis aeruginosa (Cianobacteria) en el río Paraná, aguas abajo de la represa Yacyretá (Argentina)

AbstractCyanobacteria constitute the main toxin producers in inland water ecosystems and have extensive global distribution. The presence of hepatotoxins in aquatic environments is hazardous to human and animal health; even though the presence and identification of hepatotoxic microcystins in rivers and reservoirs of the world have been confirmed by several studies in the last few years. Herein, we studied the abundance and toxicity of Microcystis aeruginosa in the Argentine section of the Paraná River at the beginning of the Middle Paraná (Corrientes Hydrometer), near Corrientes city (27º28´ S - 58º51´ W) and approximately 220 km downstream of the Yacyretá dam (High Paraná). The Paraná River basin, with a drainage area of 3.1 x 106 km2 and 3 965 km in length, is the second largest catchment of South America, after that of the Amazon. The Paraná River is the main source of drinking water supply for the Northeastern Argentine region. Phytoplankton samples were collected and environmental variables were measured in a monthly basis (exceptionally fortnightly), from March 2004 to June 2008. Fifty-eight samples were analyzed for phytoplankton density and biomass. Five samples were used for toxicity testing; the latter were obtained during the cyanobacteria blooms from 2005 to 2008. Phytoplankton counts were performed with an inverted microscope, and biomass was expressed as biovolume. Bioassays with mice and high-performance liquid chromatography (HPLC) analysis were performed to evaluate the presence of cyanotoxins. Phytoplankton mainly consisted of Cryptophyta, Chlorophyta and Bacillariophyta. Microcystis aeruginosa was identified during the warmer months each year (November to March). Density varied between 189 and 25 027 cells/mL (1-10 colonies/mL) and biomass from 0.34 to 44 mm3/L. Taking into account the number of cells, the highest abundance occurred in April 2004 (25 027 cells/mL), coinciding with the largest biovolume (44 mm3/L). All mice subjected to intraperitoneal injections with samples obtained during bloom episodes showed positive results for the presence of hepatotoxins. Three microcystins variants: LR, RR and [D-Leu1] Mcyst-LR were detected by analysis with semi-preparative high-performance liquid chromatography with diode array detector system (HPLC-PDA). This constitutes the first report of microcystins recorded during M. aeruginosa blooms in the Argentine stretch of the Paraná River at the beginning of the Middle Paraná (Corrientes Hydrometer), approximately 220 km downstream of the Yacyretá dam (High Paraná).

ResumenLas Cyanobacterias constituyen el principal productor de toxinas en ecosistemas acuáticos y tienen una amplia distribución mundial. La presencia e identificación de microcistinas hepatotóxicas en ríos y embalses de todo el mundo fue confirmada por diferentes estudios durante los últimos años. La presencia de hepatotoxinas en cuerpos de agua son riesgosas para la salud humana y animal. Se estudió la abundancia y toxicidad de Microcystis aeruginosa (Kütz.) Kütz. en el río Paraná (Argentina), cerca de la ciudad de Corrientes (27°28' S - 58°51' W), aproximadamente a 220 km aguas abajo de la represa Yacyretá. La cuenca del río Paraná, con un área de drenaje de 3.1 x 106 km2 y 3 965 km de longitud, es la segunda mayor cuenca de Sudamérica, después del Amazonas. El río Paraná es la principal fuente de abastecimiento de agua potable para el Nordeste de la República Argentina. Los muestreos se realizaron mensualmente (excepcionalmente fueron quincenales) con medición de variables ambientales, entre Marzo 2004 y Junio 2008. Se tomaron un total de 58 muestras para analizar la densidad y biomasa del fitoplancton; mientras que cinco muestras fueron utilizadas en ensayos de toxicidad, estas últimas fueron obtenidas durante floraciones de cianobacterias entre 2005 y 2008. Los recuentos de fitoplancton fueron realizados con un microscopio invertido y la biomasa fue expresada como biovolumen. Para determinar la presencia de cianotoxinas se utilizaron bioensayos con ratones y análisis con Cromatografia líquida de alta resolución (HPLC). El fitoplancton estuvo representado principalmente por Cryptophyta, Chlorophyta y Bacillariophyta. Cyanobacteria fue dominante durante los meses cálidos de cada año (Noviembre a Marzo), con alta densidad de Microcystis aeruginosa. La densidad de M. aeruginosa varió entre 189 y 25 027 cells/mL (1-10 colonies/mL) y la biomasa entre 0.34 y 44 mm3/L. Teniendo en cuenta el número de células, la mayor abundancia ocurrió en abril 2004 (25 027 cells/ mL), coincidiendo con el gran biovolumen (44 mm3/L). Todos los ratones inyectados intraperitonealmente presentaron síntomas correspondientes a hepatotoxicidad. Tres variantes de microcystinas: LR, RR y [D-Leu1] Mcyst-LR, fueron detectadas por análisis de cromatografía líquida de alta resolución con detector de diodos (HPLC-PDA). Este es el primer trabajo de microcistinas registradas durante las floraciones de M. aeruginosa en el tramo argentino del río Paraná en los inicios del Paraná Medio (Hidrómetro Corrientes), aproximadamente a 220 km aguas abajo de la represa de Yacyretá (Alto Paraná).

Desarrollo Ontogénico de la Columna Vertebral y del Esqueleto Caudal en Larvas de Rhamdia quelen en Condiciones de Larvicultura Intensiva / Ontogenic Development of the Vertebral Column and Caudal Skeleton in Rhamdia quelen Larvae in Larviculture Intensive System

Se analiza por primera vez el desarrollo osteológico de la columna vertebral y del esqueleto caudal en larvas de Rhamdia quelen mantenidas bajo condiciones controladas y con alimentación artificial. Entre los días 1 a 20 posteriores a la eclosión (dpe) se muestrearon a intervalos regulares 400 larvas, que se colorearon y transparentaron siguiendo la técnica de Taylor & Van Dike. En los primeros días de vida, las larvas presentan una notocorda recta en toda su longitud. El inicio de la formación de la columna vertebral fue observado a los 7 dpe con la aparición de las espinas neurales y hemales, y entre los 9 y 10 dpe para las tres primeras vértebras. La osificación de la columna vertebral ocurrió en sentido cráneo-caudal y fue completa a los 20 dpe. El esqueleto caudal inicia su desarrollo entre los 3 y 4 dpe, con la formación de los hipurales (H), parahipural (PH) y los radios caudales. Los H 1 al 4 se formaron como primordios cartilaginosos en la cara ventral de la porción distal de la notocorda, mientras que posteriormente lo hicieron el H 5 y el PH en el extremo distal y proximal del esqueleto caudal, respectivamente. El complejo centro ural (CCU) se osificó inicialmente en dos partes, una anterior que resulta de la combinación del centro preural 1 y el ural 1 y una posterior con el ural 2. Los primeros radios de la aleta caudal aparecieron en larvas en flexión, mientras que después de los 13 dpe, todos los ejemplares presentaron los radios principales osificados (ocho en la parte superior y ocho en la inferior). El desarrollo de la columna vertebral y del esqueleto caudal en R. quelen muestra patrones similares a los descriptos en otros peces teleósteos aunque con algunas particularidades que lo diferencian de los grupos relacionados.

The osteological development of vertebral column and caudal skeleton in Rhamdia quelen larvae under controlled conditions and artificial feeding is analyzed. Between 1 to 20 day post hatching (dph) four hundred larvae were sampled at regular intervals, and subsequently colored and transparent following the Taylor & Van Dyke technique. In the first days of life, larvae have a straight notochord throughout its length. The beginning of the vertebral column formation was observed at 7 dph with the emergence of neural and haemal spines arches, and between 9 and 10 dph for the first three vertebrae. The ossification of the vertebral column occurred in cranial-caudal direction and was complete at 20 dph. The caudal skeleton begins to develop between 3 and 4 dph, with the formation of the hypurals (H), parahipural (PH) and caudal fin rays. The H 1 to 4 were formed as cartilaginous primordia on the ventral surface of the distal portion of the notochord, and then later the H 5 and PH in distal and proximal extreme of the caudal skeleton, respectively. Central ural complex (CUC) was ossified in two parts, one anterior that is a combination of central preural 1 and ural 1 and other posterior with the ural 2. The first caudal fin rays appear in flexion larvae, while after 13 dph, all specimens had ossified principal rays (eight rays in both upper and lower lobes). The development of the vertebral column and caudal skeleton shows similar patterns to those described in other teleost fish although with some peculiarities that differentiate it from related groups.

Dietary soybean meal on growth and intestinal morphology of South American catfish, Rhamdia quelen, larvae / Farelo de soja em dietas para larvas de jundiá (Rhamdia quelen) sobre o crescimento e morfologia intestinal

The effects of the replacement of bread yeast by soybean meal in diets for Rhamdia quelen larvae on growth, survival, and intestinal morphology were analysed. Larvae were fed for 20 days with five diets: a control diet formulated with 57% of bread yeast, and other four diets in which soybean meal at concentrations of 14.25, 28.5, 42.75 and 57% was added to obtain 25, 50, 75 and 100% of bread yeast replacement. Growth and survival parameters were negatively affected by dietary soybean meal inclusion. Larvae fed control diet showed significantly higher mean weight, specific growth rate, final biomass, and survival rate than larvae from other treatments. Enterocyte height and fold width of the posterior intestine showed highest values in the control group, and an inverse linear relationship with the level of dietary soybean meal inclusion was observed, however, in the anterior intestine the morphology parameters were not affected by the diet. These results indicate that inclusion of soybean meal in diets for R. quelen larvae negatively affects growth and survival, as well as the capacity for digestion and absorption of nutrients, mainly in the posterior intestine.

Neste estudo, foi analisado o efeito da substituição de levedura de pão por farelo de soja em dietas para larvas de Rhamdia quelen no crescimento, sobrevivência e morfologia intestinal. As larvas foram alimentadas durante 20 dias com cinco dietas experimentais: uma dieta controle formulada com 57% de levedura de pão e quatro dietas em que o farelo de soja foi adicionado em 14,25, 28,5, 42,75 e 57% para obter 25, 50, 75 e 100% de substituição de levedura de pão. As variáveis de crescimento e sobrevivência foram negativamente afetadas pela inclusão da soja na dieta. As larvas alimentadas com a dieta controle apresentaram maior peso médio, taxa de crescimento específico, biomassa final e sobrevivência, diferindo significativamente dos demais tratamentos. A altura dos enterócitos e a largura das pregas no intestino posterior apresentaram valores mais elevados no grupo controle, enquanto nos demais tratamentos mostraram uma relação linear inversa com o nível de inclusão de farelo de soja na dieta. No entanto, no intestino anterior, os parâmetros morfológicos não foram afetados pela dieta. Esses resultados indicam que a inclusão de farelo de soja em dietas para larvas de R. quelen afeta negativamente o crescimento e sobrevivência, bem como a capacidade de digestão e absorção de nutrientes, principalmente no intestino posterior.

Duração da larvicultura sobre o desempenho posterior de juvenis de jundiá, Rhamdia quelen, recriados em tanques-rede / Hatchery duration influence on posterior performance of jundiá fingerlings, Rhamdia quelen, reared in cages

Realizou-se um experimento fatorial 3x2, com três repetições (n=18), a fim de avaliar o crescimento e a sobrevivência de juvenis de jundiá (Rhamdia quelen) recriados em tanques-rede e dispostos em tanques externos até os 65 dias de vida. Os peixes utilizados provêm de um sistema de larvicultura intensiva, em que foram alimentados em laboratório com três rações diferentes até os 10 e 15 dias de vida, antes de serem transferidos para os tanques-rede. Uma vez nos tanques-rede, os peixes foram alimentados até a saciedade com ração balanceada comercial contendo 28 por cento de proteína bruta. Ao final do ensaio, não foram observadas diferenças significativas entre os tratamentos para nenhum dos parâmetros estimados (P>0,05). Da mesma maneira, os valores de crescimento e sobrevivência obtidos foram similares entre os grupos de peixes transferidos aos 10 e 15 dias de vida. Os resultados demonstram que a passagem das larvas de jundiá para os tanques-rede de recria aos 10 dias de vida seria o manejo mais recomendável, diminuindo os custos da alimentação e operativos que implicam o estágio de larvicultura sob condições controladas de laboratório.

A 3x2 factorial trial with three replicates (n=18) was carried out aiming to evaluate Rhamdia quelen fingerling growth and survival rates, stocked in cages, in external ponds until attain 65 days of life. Fish used come from an intensive hatchery system, where were fed in laboratory with three different diets until attain 10 and 15 days old, before being transferred to cages. Once in cages, fishes were fed until satiation with commercial balanced diet containing 28 percent crude protein. At the end of the experience, there were no significant differences between treatments for any of the estimated parameters (P> 0.05). Similarly, the values of growth and survival obtained were similar between the groups of fish transferred with 10 and 15 days old. The results show that transference of 10 days old catfish larvae to the cages would be the more appropriate management, reducing feeding and operating costs that involves the larviculture under controlled laboratory conditions.

Fontes não-convencionais de proteína na primeira alimentação do bagre sul americano (Rhamdia quelen) / Unconventional protein sources in the first feeding of South American catfish (Rhamdia quelen)

O presente estudo teve como objetivo avaliar diferentes fontes de proteína na primeira alimentação de jundiá (Rhamdia quelen) sob condições de laboratório. Foram testadas três rações balanceadas secas: ovo de peixe (TA), hidrolisado de carcaça do peixe (TB) e fígado de frango cru (TC), na quais foram analisadas, pelo crescimento, a biomassa final produzida e a sobrevivência das larvas. O ensaio teve uma duração de 20 dias, e as rações foram fornecidas ad libitum. As larvas alimentadas com ovo de peixe apresentaram os melhores resultados com peso médio individual de 340mg, sobrevivência de 57 por cento e biomassa final de 1.350mg, diferindo significativamente dos demais tratamentos. Os resultados indicaram que a formulação de rações balanceadas com ovos de peixes fornecida na primeira alimentação de larvas de jundiá pode tornar-se uma alternativa promissora na larvicultura dessa espécie.

This study aimed to evaluate different proteins sources in first feeding of jundiá (Rhamdia quelen) under laboratory conditions. Three balanced dry rations were tested, fish roe (TA), biological fish silage (TB) and crude chicken liver (TC) evaluating specific growth rate, final biomass produced and survival rate. The experiment was performed in 20 days, and all the rations were provided ad libitum. Larvae fed with fish roe presented better results, with 340mg of individual mean weight, 57 percent of survival rate and 1.350mg of final biomass, differing significantly with the other treatments. The results show that the inclusion of fish roe in balanced rations offered at the first feeding of jundiá larvae may become a promising alternative for the hatchering of the species.