Animal welfare in modern production systems for fish
Study 4: The effects of turbid water in combination with high water temperatures on oxygen consumption, heart and ventilation rates.
The turbidity of water affects fish in various ways. One problem caused by high water turbidity is clogging of gill filaments which reduces the fish capacity to take up oxygen from the water. How severe this problem is within aquaculture is largely unknown but it is known that often when the large fish-pens are moved sediments form the bottom is suspended into the water. Shortly before the slaughter procedures start it is not uncommon that fish-pen are moved from deeper water with strong currents to calmer shallow water. The consequence for the fish is that, during a critical period when they already are stressed, from transportation, they are kept in water with high turbidity. As high levels of stress also are correlated to increased oxygen consumption which means that the reduction in oxygen uptake capacity from the turbid water occurs during a period when the demand for oxygen is high. In study 4 we aim to investigate how different levels of water turbidity effects oxygen consumption, heart and ventilation rates in fish. The study will be conducted in uninstrumented animals in using wireless measurement of all variable of interest. We will also investigate how other stressors such as transportation, high water temperatures and low levels of oxygen affects how well the animals cope with turbid water.
Fig. Study 4. Non-invasive method for cardioventilatory recordings in fresh water. (A) Schematic illustration of Rainbow trout (Oncorhynchus mykiss) in the wireless recording system. (B) Example of the raw bioelectrical potential signal. (C) Example of high-pass filtered raw signal with a cut-off frequency applied at 10 Hz to identify individual heartbeats. (D) Example of low-pass filtered raw signal with a cut-off frequency at 100 Hz and smoothed with a triangular window of 201 sample points to identify ventilatory movements. (modified from Gräns et al. 2014, PLOS ONE).