AbstractContext: Common carp Cyprinus carpio is an important aquaculture species; it is the most cultured fish for human food consumption. As many other freshwater fish species, common carp is able to biosynthesize the long chain polyunsaturated fatty acids (LC-PUFAs) from PUFA precursors by a series of elongation and desaturation reactions. LC-PUFAs play an important role in fish immune system, and their imbalance or inadequate supply could lead to negative effects on fish health. LC-PUFAs released from cell membrane phospholipids participate in the metabolism of some molecules involved in the inflammatory processes. The eicosanoids including prostaglandins and leukotriene (produced from arachidonic acid, ARA and eicosapentaenoic acid, EPA) are among the main pro-inflammatory mediators; while lipoxins (synthesized from arachidonic acid, ARA) or resolvins from the n-3 LC-PUFAs such as DHA, act as anti-inflammatory factors. However, the information on the influence of LC-PUFA amounts on fish immune system via the pro- and anti-inflammatory responses in fish in general, and in common carp in particular, is still limited. In this context, the current thesis was conducted to determine the influence of dietary fatty acids (FA) amounts from various plant oil sources on (1) growth performance, feed conversion rate, and survival; (2) FA composition; (3) immune status and (4) pro and anti-inflammatory responses in common carp.
Research strategy and methodology: Four experiments were carried out during this thesis. The first experiment was designed using six oil sources including cod liver oil (CLO), linseed oil (LO), sesame oil (SO), sunflower oil (SFO) and two blends of these plant oils – SLO (SO + LO, v:v, 1:1) and SSFO (SO + SFO, v:v, 1:1) to determine the digestibility of candidate plant oils and their influence on fish growth and FA composition in common carp. The second experiment was then carried out using three dietary lipid sources (CLO, LO and SFO) in combination with an immunostimulant (β-glucan) to assess the immune status in common carp and their immunocompetence. To determine the influence of dietary FA composition on the immune responses in cell model, the third experiment was conducted combining in vivo and in vitro approaches during which head kidney leucocytes (HKL) and peripheral blood mononuclear cells (PBMC) were isolated from common carp fed with different dietary lipid sources (CLO, SO, LO and SLO). The cells were then exposed to E.coli LPS. The last experiment was performed using the same lipid sources as in the third experiment; moreover, two additional LC-PUFA-supplemented diets (LO + ARA, LOA and SO + DHA, SOD) were tested. This experiment aimed to assess the effects of dietary plant oils enriched in n-3 (linseed oil) or n-6 (sesame oil), or supplemented with ARA or DHA on the pro and anti-inflammatory responses in HKL isolated from fish fed different oils and submitted in vitro to a LPS stimulation.
Results: The tested lipid sources did not influence the fish growth and survival but a mixture of plant oils (SLO) induced a higher feed conversion rate compared to fish oil-fed group. FA profiles in fish muscle and liver were modified by the oil sources and reflected the dietary FA composition. Fish were able to biosynthesize LC-PUFAs from PUFA precursors conducting to high level of EPA (from ALA) in LO-fed fish compared to SFO and SO-fed ones or high level of ARA (from LA) in fish fed SO and SFO-based diets compared to other experimental groups even if these LC-PUFAs were totally absent in plant oil-based diets. The mixture of SO and LO (SLO diet) induced the positive effect via balanced LC-PUFAs in fish compared to their pure plant oils. Lysozyme activity in fish fed SFO+ did not differ from SFO group; however, the overall immune status of plant oil-fed fish reared under normal conditions or challenged intraperitoneally with A.hydrophyla (at dose of 5 × 108 CFU) did not significantly differ from the one of fish fed cod liver oil. Besides, several genes involved in eicosanoid metabolism were up-regulated in SFO-fed fish reared under the normal conditions. A dietary SLO induced the highest levels of peroxidase activity and expression of gene involved in eicosanoid metabolism processes (pge2). The gene expressions of cytokines or other mediators involved in pro- and anti-inflammatory responses were dependent on time and LPS-dose, and generally, these genes were up-regulated in early stage of LPS exposure. HKLs from fish fed the SLO diet which is more balanced in PUFA precursors, or vegetable diets supplemented with ARA (LOA) or DHA (SOD), exhibited the efficient regulation of acute inflammatory processes compared to CLO leukocytes.
Conclusion: Common carp are able to use the plant-derived oils without any negative effect on growth, feed conversion rate and survival. Fish fed ALA-enriched diet have exhibited the EPA level higher than other plant oil-fed groups while the highest value of ARA levels was found in LA-enriched ones. The blend of terrestrial vegetable oils or LC-PUFA supplementation in plant oil-based diets increased the immune responses when compared with those in fish fed pure plant oils and comparable to those observed in fish oil fed fish, especially in respect to pro- and anti-inflammatory processes. A combination of in vivo and in vitro approaches help to better understand the influence of lipid sources on the immune system of common carp.
|Date of Award||18 Feb 2020|
|Supervisor||Patrick KESTEMONT (Supervisor), Thi Nang Thu Tran (Co-Supervisor), Robert Mandiki (President), Yvan Larondelle (Jury) & Daniel Montero (Jury)|