Juan C. Paggi

Feeding ecology of Macrobrachium borelli (Nobili) (Decapoda: Palaemonidae) in the flood valley of the River Paraná, Argentina

The feeding habits and selectivity of Macrobrachium borelliiwere studied by examining the stomach content of specimens from anox-bow lake across one year. M. borellii isomnivorous-carnivorous, feeding largely on members oflittoral-benthic communities. The bulk of the stomach content wasformed by oligochaetes, dipteran larvae, and a variety of organismsranging from algae to palaemonids. Copepods and cladocerans were analternative food source in winter, at low-water, when macrophytes haddeclined. Oligochaetes and dipteran larvae were positively, algae andmicrocrustaceans negatively selected.

A simple and inexpensive trap-tube sampler for zooplankton collection in shallow waters

The paper describes a new type of zooplankton sampler, which combines the concepts of the Pennak core sampler and the Schindler-Patalas plankton trap. The new sampler, called Trap Tube Sampler, consists of a PVC water pipe (1.5–2.0 m, long; 10 cm diameter) provided, at the bottom end, of a filtering unit and closing mechanism which alternatively closes the mouth of the tube and the mouth of the filtering unit. The new device is particularly suitable for collecting samples from the entire water column in shallow vegetated water bodies, fish ponds and mesocosm tanks.

Microcrustaceans escape behavior as an early bioindicator of copper, chromium and endosulfan toxicity

The purpose of this work was to experimentally analyze the impact of copper, chromium and a commercial pesticide with endosulfan on the escape behavior of two copepods (Notodiaptomus conifer, Argyrodiaptomus falcifer) and three cladocerans (Daphnia magna, Pseudosida variabilis and Ceriodaphnia dubia). The experimental assays were carried out using a novel hydraulic devise designed to mimic three-speed predator capture behavior. Two concentrations, one “high” and one “low”, were employed and the exposure time was 15 (±5) minutes. With two exceptions, the species exposed to heavy metals manifested higher ability to escape than controls. Both concentrations of the pesticide reduced the escape ability of cladocerans but copepods responded, in general, in a similar manner as for heavy metals. The immediate apparent advantage of low and early toxic effects is discussed and the high sensitivity of the escape behavior suggests that it could be a complementary endpoint to be used in future ecotoxicological tests.

A new species of Ilyocryptus (Anomopoda: Macrothricidae) from Argentina

I. elegans n.sp. from the Parana River, northeastern Argentina is proposed and its morphological features are compared with those of the apparently related I. agilis. Its outstanding characteristics are the long 2rd to 5th setae of ventral margin of the valves, the rudimentary nature of defensive setae, the low number of spines in the preanal lobe of postabdomen and the unequality of the length of the setae in the outer distal lobe of first trunk limbs.Finding of this new species suggests that I. agilis would be a complex of species and its records should be revised.

Daphnia (Cienodaphnia) menucoensis (Anomopoda; Daphniidae): a new species from athalassic saline waters in Argentina

Daphnia (Ctenodaphnia) menucoensis n. sp. is described from various localities in arid and semiarid Argentina. D. menucoensis has no ocellus, and a characteristic head, fornices, ephippium and denticular arrangement of postabdomen in females and males. The species belongs to a group, along with D. mediterranea, D. ‘dolichocephala’ Negrea 1984, and D. salina, sharing ecological and morphological characteristics.

A new species of Ilyocryptus (Crustacea: Anomopoda) from the River Paraná basin, Argentina

A new species of Ilyocryptus Sars from several localities in River Paraná basin, is described and figured. By the presence of a lateral process on the valves I. paranaensis n.sp. resembles I. cornutus Mordukhai-Boltovskoi & Chircova, but it shows several morphological differences in the shape and the armature of the postabdomen and in the antennal formula.

Assessment of the urbanization effect on a lake by zooplankton

The present study was aimed at comparing zooplankton composition and abundance between the western shore of the shallow lake Setúbal, on which the city of Santa Fe is founded, and the eastern shore, whose environmental impact is scarce or null. Five samplings were carried out in 14 stations, under different seasonal conditions, hydrometric levels, and volumes of previous rainfalls. The values of conductivity, pH, transparency, specific richness, and abundance of macro and microzooplankton showed significant differences between both shores. The highest zooplankton density, with a proportion of Bdelloid rotifers of up to 20% of the total abundance, was associated with the urbanization of the impacted shore. The volume of the lake and its fast turnover rate would buffer the impact of contamination, as indicated by a certain degree of eutrophication, which is more evident at lower hydrometric levels and higher temperatures.

Behavioural responses of two cladocerans and two copepods exposed to fish kairomones

In natural predator–prey interactions, chemical communication is one of the most advantageous strategies for prey organisms because they can anticipate possible harm by means of phenotypic changes. This study compares the changes in the behaviour of four freshwater zooplankton species in the presence and absence of infochemicals from the same predator. The studied organisms are two copepods and two cladocerans living in highly variable freshwater environments. The analysis is focused on two predator defensive behaviours: a pre-encounter and a post-encounter response. First, we analysed the diel vertical migration (DVM) of the organisms inside 150 cm long transparent plastic tubes. Second, we used a novel hydraulic apparatus to quantify their ability to escape from a potential predator. The results revealed that the species have different behavioural patterns in the absence of infochemical. The differences were mainly in the way DVM developed and reflect their life histories and adaptive strategies relative to their natural environment. When faced with kairomones, the escape ability of the organisms was enhanced in all cases and DVM changed, although not always in agreement with the expected patterns. The interaction between each species and the multiple environmental components is discussed.

Horizontal distribution of rotifers in a subtropical shallow lake (Paraná floodplain, Argentina)

Fil: Jose, Susana Beatriz. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto Nacional de Limnologia. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina

Two new species of Diaptomidae (Crustacea: Copepoda: Calanoida) from the Neotropical Region (Paraná River)

Two new species of Diaptomidae were found in the Middle Paraná River. The new species are referred to as “Diaptomus” curvatus sp. nov. and “Diaptomus” frutosae sp. nov. Important character states in “Diaptomus” curvatus include: right fifth leg with a well-developed endopod and with the lateral spine of the second exopod segment curved and longer than the segment on which it is inserted, plus the presence of a large dorsal process on urosomite 4 of the male. For “Diaptomus” frutosae they include: a differentiated hook-like process on segment 20 with chitinous protuberances at base of male right antennule; the last segment of the right leg 5 of male is triangular, and the lateral spine inserted distal to mid-level of this segment. Both species are placed in “Diaptomus” sensu lato as a temporary placement. http://www.zoobank.org/urn:lsid:zoobank.org:pub:FECDD6C4-C0AC-4043-ADDD-F29539B451F0