Maturation, sex ratio and fecundity of the Nile perch Lates niloticus (L.) (Pisces: Centropomidae) in Lake Chamo, Ethiopia

Length-weight relationship, length at first maturity and sex ratio of the Nile perch Lates niloticus (L.) were studied from 342 fish samples collected between February 1995 and May 1996. The relationship between total length (TL) and total weight (TW) for both sexes was curvilinear and statistically significant. The regression equation for the males was TW=0.0044TL3.27 (r2=0.978,

Fluctuaciones temporales en el fitoplancton y contenido de microcistinas intracelulares en cuatro lagos Nicaragüenses

La contaminación de los ecosistemas acuáticos por el enriquecimiento de nutrientes permite la proliferación de microalgas o florecimientos que pueden tener potencial tóxico si los grupos dominantes son cianobacterias. Por lo que este estudio tuvo como objetivos conocer las fluctuaciones temporales de las especies fitoplanctónicas presentes en cuatro lagos nicaragüenses (Cocibolca, Xolotlán, Masaya y Tiscapa), con énfasis en las cianobacterias y estimar su potencial tóxico por microcistinas. Se realizaron 11 muestreos en los lagos de interés en los que se analizaron el contenido de Clorofila a, fitoplancton cuantitativo, identificación taxonómica hasta el nivel de género y especies así como el contenido de microcistinas por ELISA. La Clorofila a osciló entre un valor no detectado en el Lago Xolotlán (noviembre) y 37 μg/l detectados en Tiscapa (agosto). Los géneros fitoplanctónicos más representativos detectados durante la mayor parte del período muestreado en tres de los cuatro lagos nicaragüenses estudiados (Cocibolca, Tiscapa y Masaya) fueron cianobacterias, entre los que se distinguen Anabaenopsis, Merismopedia, Chroococcus y Lyngbya. El Lago Xolotlán presentó dominancia de taxas de diatomeas (Stephanodiscus sp, Synedra sp, y Cyclotella meneghiniana). Los resultados de microcistinas muestran valores bajos (< 0.003 hasta 0.069 μg/l) en los cuatro lagos estudiados, siendo los lagos Xolotlán y Masaya los que presentaron las mayores concentraciones en los meses de mayo y julio, respectivamente. Al comparar estos resultados con los reportados para ecosistemas lacustres del mundo para el mismo período se puede inferir un bajo potencial tóxico por microcistinas en los cuatros lagos nicaragüenses. Sin embargo, no se puede descartar la toxicidad debida a otras toxinas naturales dada la dominancia de géneros de cianobacterias por lo que se recomienda seguir realizando monitoreos de este tipo e incluir en el conteo a pico-cianobacterias

Cyanotoxin production in seven Ethiopian Rift Valley Lakes

We hypothesized that unusual deaths and illnesses in wild and domestic animals in lake areas of the Rift Valley south of Addis Ababa were caused by toxic cyanobacteria. In the first cyanotoxic analyses conducted in samples from Ethiopia, we found lakes Chamo, Abaya, Awassa, Chitu, Langano, Ziway, and Koka all had concentrations of microcystins (MC) ranging from trace to hazardous, whereas only traces less than limits of detection (LOD) of cylindrospermopsin (CYN) were found. In the December 2006 dry season we sampled the lakes for analyses of MC, CYN, species structures, and calculations of cyanobacteria biomass. We used the Uterm&ouml;hl technique to analyse cyanobacterial biomass and monitored MC toxins using HPLC-DAD, LC-ESI-MS-MRM, and ELISA-test and CYN with HPLC-DAD and ELISA. The various toxicity tests coincided well. In 4 of the lakes (Chamo, Langano, Ziway, and Koka), the inter-lake range of total MC concentration was 1.3&ndash;48 &mu;g L-1; in 3 (Abaya, Awassa, and Chitu), we found only traces of MC. Microcystis aeruginosa was the dominant species, with Microcystis panniformis, Anabaena spiroides, and Cylindrospermopsis spp. as subdominants. The MC concentration, especially in Lake Koka, exceeded levels for serious health hazards for humans, cattle, and wildlife

Lipid composition and food quality of some freshwater phytoplankton for cladoceran zooplankters

Abstract. The nutritional value of several planktonic algae was tested by means of feeding trials with three cladoceran zooplankters. The algae were monocultures and included two blue-greens, four greens and four flagellates with a size range of 5-48 u,m. The specific growth rates of the zooplankters were chosen as the measure of the nutritional value of the algae. The three cladocerans showed large differences in growth rate in the different algae, but the two cryptomonads were without doubt best suited as food for all. The fatty acid composition for the cryptomonads were different from the other algae. They contained high percentages of the polyunsaturated fatty acids 20:5u)3 (EPA) and 22:6w3 (DHA), which also are common in fish. It is suggested that the lipid composition is a probable factor determining the nutritional quality of the algae