Community Research and Development Information Service - CORDIS

Testing the biorheological properties of water: the ichthyoviscometer

Intertidal mudflats are important nursery grounds for juveniles of many fish species. However, they are being used increasingly to farm bivalve molluscs, which produce large amounts of organic biodeposit, rich in exo-polyssacharides (EPs), overlying the mud. Fish such as sole, Solea solea, hide in this fluff from potential predators, but the energy consumed by respiring the fluff may be high due to its biorheological properties (viscosity).

To investigate the potential impact of EPS on the bioenergetics and ventilation of juvenile sole we developed an ichthyoviscometer. We developed this method to measure the rheological properties of fluids and suspensions, including fluff, at scales encompassing those in fish mouth and gill cavity.

We found that the rheological behaviour of fluff is close to that of a gel with a yield stress strongly dependent on particulate organic matter concentration ([POM]). This allowed us to model fluff flow through the gill channels in living sole as a function of fish size and [POM], showing that in a 26g sole, fluff would halve flow at a [POM] value of 3.2g/L, and stop it at 3.4g/L.

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