Most animals and plants have a ‘biological clock’ which influences their periods of activity and their internal physiology. It has often been assumed that sea creatures living at extreme depths and animals living in caves are exceptions to this rule, as both environments receive no sunlight and therefore have no rhythm of change from day to night.
 

The aim of the study is to scientifically test this widely held assumption. The initial focus of our investigation is a species of fish which are unique to North East Mexico. The fish have evolved in a cave environment, and this has led to the loss of pigmentation in their scales and the loss of their eyes. Experimentation in lab conditions has already shown that these cave fish still have the genes necessary for a functional biological clock. The question to which we are seeking an answer with this field experiment is whether or not this potential is used within the cave environment. And if it is, how does it function without sunlight? The study using the RS Hydro technology is being conducted by a team of scientists from a variety of academic fields, and includes team members from the United Kingdom, Mexico, the USA, France and Japan.
 

Although the conditions in the cave are supposedly constant this can’t be taken for granted. To get a scientifically accurate assessment of all factors that could influence the behaviour of the fish over the period of the study it is necessary to carefully monitor conditions in the aquatic environment. RS Hydro were able to provide a complete solution for this application. A Troll 9500 water quality sonde and a Rugged Reader are being used to assess changes in water conditions.
 

The Troll 9500 water quality sonde from RS Hydro can be fitted with up to nine field replaceable sensors that are capable of measuring level, temperature, dissolved oxygen, turbidity, pH/ORP, conductivity, ammonia, nitrate and chloride. The sensors of the Troll 9500 water quality sonde can be calibrated in under five minutes using Quick Cal solutions. The Troll 9500 water quality sonde also contains a data logger and the internal batteries can be left in-situ for up to 12 months without additional power.
 

By monitoring the gene function of the fish, tracking their behaviour using infra-red cameras and constantly assessing changes to their aquatic environment, we hope to provide a definitive answer to the question ‘can Mexican cave fish tell the time?’