Macro-Rheology Characterization of Gill Raker Mucus in the Silver Carp, Hypophthalmichthys molitrix

Summary

This protocol presents a method to perform rheology characterization of mucus that resides on gill rakers (GRs) of the silver carp. Viscoelastic characteristics of GR-mucus, obtained by measuring viscosity, storage and loss moduli, are evaluated for the apparent yield stress to understand the filter feeding mechanism in GRs.

Abstract

The silver carp, Hypophthalmichthys molitrix, is an invasive planktivorous filter feeder fish that infested the natural waterways of the upper Mississippi River basin due to its highly efficient filter feeding mechanism. The characteristic organs called gill rakers (GRs), found in many such filter feeders, facilitate the efficient filtration of food particles such as phytoplankton that are of a few microns in size.

The motivation to investigate the rheology of the GR mucus stems from our desire to understand its role in aiding the filter feeding process in the silver carp. The mucus-rich fluid, in a ‘thick and sticky’ state may facilitate the adhesion of food particulates. The permeation and transport through the GR membrane are facilitated by the action of external shear forces that induce varying shear strain rates. Therefore, mucus rheology can provide a vital clue to the tremendous outcompeting nature of the silver carp within the pool of filter feeding fish. Based on this it was posited that GR mucus may provide an adhesive function to food particles and act as a transport vehicle to assist in the filter feeding process.

The main objective of the protocol is to determine the yield stress of the mucus, attributed to the minimum shear stress required to initiate flow at which irreversible plastic deformation is first observed across a structured viscoelastic material. Accordingly, rheological properties of the GR mucus, i.e., viscosity, storage, and loss moduli, were investigated for its non-Newtonian, shear-thinning nature using a rotational rheometer.  

A protocol presented here is employed to analyze the rheological properties of mucus extracted from the gill rakers of a silver carp, fished at Hart Creek location of the Missouri River. The protocol aims to develop an effective strategy for rheological testing and material characterization of mucus assumed to be a structured viscoelastic material.

Introduction

The silver carp, Hypophthalmichthys molitrix, is a planktivorous filter feeder and an invasive species that has infiltrated several natural waterways in the United States. This species was initially introduced in the upper Mississippi River basin to control algal blooms^1,2,3. The silver carp is an extremely efficient feeder. Typically, its consumable food particle sizes range from 4 to 20 μm to larger zooplankton that are around 80 μm^3,4,5. This species has outcomp....

Protocol

1. Preparation of the mucus solutions of various concentrations

NOTE: Three concentrations of the mucus solution (400 mg/mL, 200 mg/mL and 100 mg/mL with approximate volumes, 1 mL, 1 mL, and 2 mL, respectively) are prepared for this experiment. 

1. To calculate the mass of the mucus, measure the average mass of the vials with (M_with-mucus ; mg) and without mucus (M_vials ; mg). Then subtract the mass of the vials with mucus with that without mucus (M_mucus = M_with-mucus - M_vials ; mg).  
2. Dilute the ....

Results

In this section, we present the results of the experiments on GR mucus using a rotational rheometer with a cone geometry (40 mm diameter, 1° 0’ 11’’) and a Peltier plate. The experiments helped in characterizing the non-Newtonian, shear-thinning behavior of the GR mucus and the apparent yield stress depicting the mucus transition from a gel-like material to a fluid-like material. The representative results entail quantitative descriptions of low-torque limits and secondary flow effects of the rotational rheometer instrum.......

Discussion

One of the main objectives of developing this protocol is to establish that it is well-suited for rheological characterization of GR mucus when very small sample volumes are available. We acknowledge that more samples from a school of silver carp are needed to fully characterize the rheological properties of the GR mucus and the data presented herein are not a generalization across the entire silver carp population. Our technique is justified because of its efficacy with rheological characterization of small sample volum.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Materials
Kim Wipes	VWR	470224-038	To clean Sample from plate
Gloves	VWR	89428-750	To prevent contamination of sample
Pipette	VWR	89079-974	To transport sample from vial to rheometer
Pipette Tips	Thermo Scientific	72830-042	To transport sample from vial to rheometer
Shaker	VWR	89032-094	To homogenously mix sample of mucus
Vials	VWR	66008-710	Contains measured sample volumes
Weigh Scale	Ohaus	Scout –SPX Balances	To weigh mass of mucus samples
Chemical Reagents
De-Ionized Water (H20)	-	-	Liquid
Sterile 70% Isopropanol (C3H8O)	VWR	89108-162	Liquid
GR Mucus
100 mg/mL concentration, 2mL	-	-	Viscoelastic Material
400 mg/mL concentration, 1mL	-	-	Viscoelastic Material
200 mg/mL concentration, 1mL	-	-	Viscoelastic Material
Software
MATLAB	Mathworks	R2017a	Data analysis, post-processing and graphical representation
Trios	TA Instruments	v4.5.042498	Rheometer instrument control and analysis software