PT  - JOURNAL ARTICLE
AU  - Willis, Jay
AU  - de Perera, Theresa Burt
AU  - Poncelet, Guillaume
AU  - Thomas, Adrian
TI  - A new method for measuring fish swimming patterns in shallow water and a previously undescribed swimming gait
AID  - 10.1101/853853
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 853853
4099  - http://biorxiv.org/content/early/2019/11/25/853853.short
4100  - http://biorxiv.org/content/early/2019/11/25/853853.full
AB  - Hill stream loaches are fish which live their entire lives in close contact with rock. They have elaborate physical adaptations to fast flow, adherence to substrate, and movement in very shallow water. Here we describe a method for observing how they swim in detail. There are many similarly shaped rheophilic fish, insects, and amphibian larvae, which live in fast flowing water, and a method of observing their swimming modes has wide potential application. We measured the deflection of the water surface around a swimming fish by viewing a fixed pattern on the bottom of the tank through the water surface. This is a Schlieren method in which the movement or other physical properties of a medium are derived from the deflection of a pattern viewed through that medium. We used this method to describe a new type of swimming gait which is likely to be common among small rheophiles – pulse swimming mode – in which thrust is produced in a series of discrete impulses. The method of analysis described here is beneficial in that the fish is allowed to swim freely in relatively normal conditions without the use of intrusive equipment such as lasers, dyes, or additives to the water, and the pattern of thrust is viewed directly against the skin of the fish rather than being inferred from the wake pattern behind the fish. The method is also low cost and easily set up.