2.4. Coelomic fluid parameters
In a separate series of experiments coelomic fluid samples were collected
from the base of the arm with a 1 ml airtight Hamilton syringe
and 21 gauge needle. To avoid adversely affecting animals by repeated
collection of large samples from the same starfish, separate animals
(n = 7 of 350–450 g) were used at each time period and each for
experimental temperature. Oxygen partial pressure (PO2) and pH
were measured immediately using a Fibox-3 O2 and a pH mini-V2
analyser (PreSens, Regensburg, Germany). The PreSens systems were
connected to fibre optic probes and sensor spots which were housed
in a thermostated Cameron chamber. The oxygen probes were calibrated
with air and nitrogen mixtures, delivered using a Cameron Instruments
gas-mixing pump. Coelomic fluid samples (approximately
300 μl) were injected into the port of the Cameron chamber and allowed
to equilibrate for 3 min until the readings stabilised. The Cameron
chamber temperature was adjusted throughout the experiment to parallel
the changes in the coelomic fluid temperature of the experimental
animals