Sérgio Renato Noguez Piedras

Macroinvertebrados bentônicos como indicadores de qualidade de água na Barragem Santa Bárbara, Pelotas, RS, Brasil

The objective of this work was to study the impact of two tributaries from the Santa Barbara Dam on this environment using the occurrence of zoobenthics and some water chemical characteristics. Monthly gathering and analysis from the water and zoobenthics were done during nine months in the tributaries Sanga da Barbuda and Sanga Passo do Cunha as well as in the inner part of the accumulation basin in the Santa Barbara dam. The results demonstrate that, though Sanga da Barbuda and Sanga Passo do Cunha present chemical characteristics lower than the recommended but still in the limits acceptable by the law that regulates the water quality standards for the supply, these tributaries are being diluted in a satisfactory way in the accumulation basin in the Santa Barbara dam. The study of the relations between chemical variables and zoobenthics show a significant correlation between low levels of dissolved oxygen and the presence of Oligochaeta; moreover, the increase of Oligochaeta indicates a situation of anoxia in the Santa Barbara Dam.

Alimentação do peixe-rei (Odontesthes bonariensis, Atherinopsidae) nas lagoas Mirim e Mangueira, Rio Grande do Sul, Brasil

Natural feeding of silverside (Odontesthes bonariensis Cuvier & Valenciennes, 1835) was studied in the Mirim and Mangueira lagoons, State of Rio Grande do Sul, Brazil. The stomach content of 60 silverside individuals (Odontesthes bonariensis) from that lagoons showed that this species has a wide food spectrum. A wide range of food items was consumed without affecting fish growth, since similar body conditions were observed. In Mangueira lagoon, crustaceans (Isopoda) represented 65% of the diet, whereas in Mirim lagoon, mollusks (Bivalvia and Gastropoda) represented 70% of the identified stomach contents.

Lethal concentration (CL50) of un-ionized ammonia for pejerrey larvae in acute exposure

Ammonia results from decomposition of effluents organic matter, e.g. feed wastes and fish faeces. Its un-ionized form can be toxic because diffuses easily through fish respiratory membranes, damaging gill epithelium and impairing gas exchanges. The objective of this work was determining the 96-hour CL50 of un-ionized ammonia for newly hatched pejerrey Odontesthes bonariensis larvae. Trials were set up completely randomized design, with three different concentration of un-ionized ammonia (0.57, 0.94, and 1.45 mg L-1 NH3-N) and a control treatment (n = 3). Experimental units were 20-L, aerated aquaria stocked with 20 larvae (average weight 3.9 mg). Pejerrey larvae exposed to un-ionized ammonia during 96 hours present 50% mortality at 0.71 mg L-1 NH3-N.

Toxicidade aguda da amônia não ionizada e do nitrito em alevinos de Cichlasoma facetum (Jenyns, 1842)

The nitrogen is derivates in water presence indicates active biological processes influenced by organic pollution, being able, in high concentrations, to cause physiological damages, even mortality in aquatic organisms. In order to determine the lethal effect of the un- ionized ammonia and of the nitrite, fingerlings of cara (Cichlasoma facetum) have been exposed, during 96 hours, to diverse concentrations of such composites: from 0 to 4.60 mg.L-1 of NH3 N, and from 0 to 6.68 mg.L-1 of NO2. The calculated CL50, for 96 hours, was 2.95 mg.L-1 of un-ionized ammonia. The highest concentration of nitrite, 6.68 mg.L-1, caused the mortality of 45.63% of the fingerlings of cara in 96 hours. The factorial analysis of the mortality variance in relation to the concentration of agents, showed the interaction between both products, resulting the increase of mortality of fingerlings of cara.

Alimentação de alevinos de peixe-rei (Odontesthes bonariensis) com dietas naturais e artificiais

An experiment was run to evaluate three feeding methods for pejerrey fingerlings, in a complete randomized design with four replications. Each experimental unit consisted of a 20L aquarium and 20 three days old fingerlings. For six weeks, three times a day, fish received the following diets: T1= mash diet; T2= mash diet + zooplankton; T3= zooplankton. Results showed that zooplankton promotes better fingerlings growth and survival. Fish fed with mash diet showed significantly lower growth and survival, but acceptable considering actual status of nutrition studies for pejerrey.

Probiotic actions of Bacillus cereus var. toyoi and Saccharomyces boulardii in silver catfish (Rhamdia quelen) larvae culture

The objective of this study was to evaluate the use of Bacillus cereus var. toyoi and Saccharomyces boulardii as probiotics to improve Rhamdia quelen culture. Six hundred larvaes (0.16±0.07 g) were divided in three replicate tanks (25-L recirculation, 20 oC, photoperiod of 12 h light/12 h darkness) per treatment and were randomly assigned to the following treatments: Bacillus cereus var. toyoi; Saccharomyces boulardii; B. toyoi and S. boulardii; and control (without probiotic addition) for a period of 30 days. The fish were fed five times daily (56% crude protein - Supra alevino inicial®) and the probiotics were applied in water once a day. The doses of probiotics were 5 × 108 and 2 × 109 CFU (colony forming unit)/mL for B. cereus var. toyoi and S. boulardii, respectively. Both probiotics have an inhibitory effect in vitro against Vibrio carchariae and are able to grow in media prepared with fishery water; however, no effect was observed on growth parameters when they were administered to Rhamdia quelen larvae.

Efeito da suplementação de metionina e/ou lisina no crescimento e na sobrevivência de alevinos de peixe-rei (Odontesthes bonariensis)

Para avaliar o efeito da suplementacao de metionina e lisina sobre o desempenho de alevinos de peixe-rei (Odontesthes bonariensis), estabeleceu-se um experimento completamente casualizado com quatro tratamentos. A dieta T1 (controle) continha as concentracoes de metionina e lisina disponiveis nos produtos usados na formulacao da mesma. A dieta T2 foi suplementada com 4,76% de DL-metionina; a dieta T3, com 4,76% de L-lisina; e a dieta T4, com 4,54% de DL-metionina e 4,54% de L-lisina. As dietas suplementadas com metionina foram mais eficientes que a dieta-controle e a suplementada apenas com lisina, pois esta nao apresentou diferenca em relacao a dieta-controle, comprovando que a quantidade de lisina disponivel nos produtos utilizados na elaboracao das dietas atende as necessidades dos alevinos de peixe-rei. A quantidade de metionina disponivel nestas formulacoes e insuficiente para o bom desempenho dos alevinos, devendo ser suplementada.