Effects of water temperature, PIT-Tagging and mimicked bacterial infections on immune function in crucian carp (Carassius carassius)

Abstract

Immune function is an important parameter in almost all organisms which determines their ability to survive and fight off pathogens. Immune function (like other physiological functions) is temperature dependent. So that opens the question of how immune function is in poikilotherms. Being poikilotherm means that the species depends on the ambient temperature for body heat regulation. I used crucian carps (Carassius carassius) to study if different water temperatures affect immune function and if immune challenges trigger different immune responses under different water temperatures. In the first experiment, I used three different temperatures (7⁰C,15⁰C,22⁰C) to determine baseline immune function at different temperatures. For the second experiment, I used an immune challenge treatment with LPS (Lipopolysaccharide) and combined it with PIT-tagging (Passive Integrated Transponder) treatment to see if and how those treatments caused an immune response and if it different among temperatures. PIT tagging is not a direct immune challenge, but an injection of a foreign matter under the skin of fish. I wanted to investigate if PIT tagging alone would trigger an immune response when comparing it with PIT+LPS. I found that the baseline immune function did not vary between the different temperatures. However, in experiment 2 there was some variation between treatments and temperatures, suggesting that treatment and timepoints in blood sampling might influence changes in the innate immune response. Finally, I measured organ sizes of heart and liver and found that temperature influences the size of the organs in experiment 2 but not in experiment 1; organ sizes were largest at the high and low temperature. This study provides further insights into temperature and its role for immune function and immune response.

Popular Abstract

Challenging the immune system in crucian carps

All animals including humans have an immune system, which acts as the line of defense against invading foreign substances. Physiological functions, such as immune function, are usually temperature dependent and work best under certain temperatures. Mammals/humans and birds have a constant body temperature and hence physiological functions like immune function are adapted to function under that temperature. Fish, however, do not have a constant body temperature, but their body temperature depends on the environmental temperature. This opens the question how immune function works if the body temperature of fish changes markedly throughout the year. From a few degrees above zero in winter to temperatures above 20⁰C in summer. I studied if immune function differed under different water temperatures and if immune challenges caused differed immune responses under different water temperatures.
Crucian carps (Carassius carassius) were used as a model for this study and they were housed in three different temperatures (7⁰C,15⁰C,22⁰C). A total of 144 fish were used in my study and I kept 48 fish under each temperature. Six fish were housed in each tank, which was divided into 2 compartments by a permeable plexiglass slab, hence 3 fish per compartment.

I divided my study into two experiments. In the first experiment, I studied the baseline immune function under the three different temperatures. Baseline immune function is generally the first line of defense, i.e. the ability of an organism to detect and prevent pathogens from entering the system. In the second experiment, I studied the innate immune response, which is the response when an antigen enters the system. I used an immune challenge called LPS that mimics a bacterial infection. Furthermore, I tested if marking techniques like PIT-tagging (Passive Integrated Transponder) can cause an immune response. Hence, three treatment groups were used for experiment 2: control (normal fish), PIT tagging and PIT+LPS.

To be able to measure immune function, I blood sampled all fish and used the plasma in the lab to measure immune function. Apart from this, the organ size was also measured to see if there is a difference in size of the heart and liver between temperatures and treatments. For experiment 1, the baseline immune function did not differ between the three different temperatures. There was no difference in the size of the organs between temperatures.

For experiment 2, the innate immune response differed between temperature and treatments and it peaked at 22⁰C but there was no difference when the immune response was tested at separate temperatures. The size of the liver and heart differed between the temperatures but did not differ between the treatments. But most of my results did show a trend that changes in temperature affects the baseline immune function and treatment such as PIT tagging and immune challenges affects the innate immune response.

Master’s Degree Project in Biology, 30credits, 2020
Department of Biology, Lund University

Advisor: Arne Hegemann
Aquatic Ecology

• author: Saravana Bhavan Venkatachalam, Ashwin Kumarr
• supervisor: Arne Hegemann
• organization: Degree Projects in Biology
• course: BION03 20192
• year: 2020
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9029179
• date added to LUP: 2020-09-14 11:12:36
• date last changed: 2020-09-14 11:12:36