Dataset for article Freshwater mussel Anodonta cygnea removes pathogenic oomycete Saprolegnia spp. spores from water, and decreases spore germination rate and infectivity

This dataset contains the raw data used in analyzes for the article Freshwater mussel Anodonta cygnea reduces concentration, germination rate, and infectivity of pathogenic oomycete Saprolegnia spp. spores

The dataset was compiled for a study in which we studied (1) the capacity of swan mussels (Anodonta cygnea) to filter particles (spores and hyphae fragments) of cultured Saprolegnia ferax and S. diclina from water, and the effect of mussel biofiltration on (2) infective spore concentration and the germination rate of S. diclina spores, and (3) the effect of mussel biofiltration on occurrence of saprolegniosis on fish eggs. 

Materials & methods

Experiments were conducted in 4 liter glass aquaria containing 1 (particle filtering experiment, infective spore concentration and germination rate experiments) or 2 (infectivity to fish eggs experiment) swan mussels. Test tanks were filled with 2 (particle filtering experiment, infective spore concentration and germination rate experiments) or 3 (infectivity to fish eggs experiment) liters of water containing known concentrations of Saprolegnia spp. derived particles and spores, and the effect of mussel biofiltration was monitored for 24 hours in each trial.

Mussel lengths were measured at the end of the experiments with Vernier calipers to the nearest mm to calculate mussel dry mass estimates. The dry weight estimate for the mussels was calculated with the formulae "𝑑𝑤=0.12𝑒0.31𝑙", where l is mussel length in cm (Ravera & Sprocati, 1997).

Particle concentration in the test aquaria was measured with a CASY Electronic Cell Counter and Analyzer (OLS-OMNI Life Science GmbH & Co. Bremen, Germany, with a capillary pore size of 60 µm, except for of one Mussel treatment tank, with too many particles for reliable counting with CASY, when spore concentration was determined with a Bürker hemocytometer (bright-line, Marienfeld, Germany) instead. Number of replicates in the particle biofiltering experiment was 24, of which 6 were Control, and 18 Mussel treatments. One of the Mussel treatments had to be discarded as an outlier, as the mussel individual in the tank released particulate matter in the tank at the point of transfer, rendering the water too murky to be sampled during timepoints 1, 2, and 4 hours.

Saprolegnia diclina culturing was done on oomycete-optimized PG-1 culturing medium on 9cm petri plates from 20 µL samples collected from Control and Mussel aquaria water and sediment after 24 hours of biofiltering. Colonies and ungerminated spores were counted visually with an inverted microscope (Olympus IMT-2). Concentration of germinated spores in the water and sediment of Control and Mussel aquaria was calculated from the number of S. diclina colonies found on culturing plates after 24 h incubation. Germination rate for S. diclina spores was calculated by dividing the number of Saprolegnia colonies (individual mycelial growths) with the total number of found colonies and ungerminated spores. Number of replicates was 8 for both Control and Mussel treatments for water, and 7 for both Controls and Mussels for sediment.

Infection rate for fish eggs (African sharptooth catfish, Garias clariepinus) was calculated by dividing the number of infected eggs with the total number of eggs. Infection was detected visually with a preparation microscope. Number of replicates for infectivity to fish eggs experiments was 12, of which 4 were Control and 8 Mussel treatments, with 2 mussels in each Mussel aquaria.