A stimulation of thrombocyte production was also observed by
Capkin and Altinok [49] in rainbow trout fed of the probiotics
Enterobacter cloacae and Bacillus mojavensis. Similar results were
obtained by Barbosa [50], who found higher thrombocyte values in
Centropomus parallelus fed the probiotic Lactobacillus plantarum for
10 weeks.
Changes in catecholamine, corticosteroid hormone, and blood
nutrient levels may be used to monitoring the responses to stress
[51]. No significant differences were observed in the plasma cortisol
and glucose levels of fish, even when these were raised at the high
stocking density. The fish subjected to chronic stress situations may
not exhibit changes or present only a slight change in their cortisol
and glucose levels change [25,52e54]. A prolonged period of stress
exposure can cause a suppression of the endocrine system [55] or
may cause the animal to become accustomed to this condition. In
some cases, changes cannot be observed in the plasma glucose level
because the stress quickly consumes the energy reserves to maintain
homeostasis [56].