Depletion of Essential Fatty Acids in the Food Source Affects Aerobic Capacities of the Golden Grey Mullet Liza aurata in a Warming Seawater Context

Abstract

The objective of this study was to evaluate the combined effects of thermal acclimation and n-3 highly unsaturated fatty acids (n-3 HUFA) content of the food source on the aerobic capacities of fish in a thermal changing environment. The model used was the golden grey mullet Liza aurata, a species of high ecological importance in temperate coastal areas. For four months, fish were exposed to two food sources with contrasting n-3 HUFA contents (4.8% ecosapentaenoic acid EPA + docosahexaenoic acid DHA on the dry matter DM basis vs. 0.2% EPA+DHA on DM) combined with two acclimation temperatures (12°C vs. 20°C). The four experimental conditions were LH12, LH20, HH12 and HH20. Each group was then submitted to a thermal challenge consisting of successive exposures to five temperatures (9°C, 12°C, 16°C, 20°C, 24°C). At each temperature, the maximal and minimal metabolic rates, metabolic scope, and the maximum swimming speed were measured. Results showed that the cost of maintenance of basal metabolic activities was particularly higher when n-3 HUFA food content was low. Moreover, fish exposed to high acclimation temperature combined with a low n-3 HUFA dietary level (LH20) exhibited a higher aerobic scope, as well as a greater expenditure of energy to reach the same maximum swimming speed as other groups. This suggested a reduction of the amount of energy available to perform other physiological functions. This study is the first to show that the impact of lowering n-3 HUFA food content is exacerbated for fish previously acclimated to a warmer environment. It raises the question of the consequences of longer and warmer summers that have already been recorded and are still expected in temperate areas, as well as the pertinence of the lowering n-3 HUFA availability in the food web expected with global change, as a factor affecting marine organisms and communities.

Effects of extraction method and storage of dry tissue on marine lipids and fatty acids

“…Marine lipids are commonly extracted with the solvent mixture of Folch et al [9] (chloroform:methanol; 2:1, v/v) using different methods. The most popular methods use automats such as Soxhlet and Accelerated Solvent Extraction (e.g., [10][11][12]), potter homogenizers (e.g., [13][14][15]) or leave the solvent to work on ground tissue (e.g., [16][17][18]).…”

Ocean warming combined with lower omega-3 nutritional availability impairs the cardio-respiratory function of a marine fish

“…These contrasting results for the same species suggested potential interactions between HUFA food content and acclimation temperature on fish physiology. This interaction was recently demonstrated in a species highly tolerant to temperature variations, the golden grey mullet, Chelon auratus: the detrimental effects of a low HUFA diet were greater in warmer conditions (20°C versus 12°C), resulting in greater energy expenditure to reach a given swimming speed (Vagner et al, 2015). Highlighting these combined effects is of particular importance given the strong seasonal temperature variations that occur in temperate coastal areas, and the predicted scenario of a 3°C increase in ocean water temperature by 2100 (IPCC, 2013).…”

“…We used golden grey mullets, Chelon auratus (Risso 1810), from the same experimental groups as those used by Vagner et al (2015): they were exposed to two highly contrasting HUFA diets (a high and a low HUFA diet), chosen according to the needs defined for several fish species, and two contrasting environmental acclimation temperatures that are representative, respectively, of mean winter (12°C) and mean summer (20°C) temperatures in the Pertuis Charentais area (Rochebonne, France). Their cardio-respiratory performance was then measured at the individual level in terms of metabolic rates and associated swimming effort.…”

“…Diets were formulated taking a standard diet as the reference (1.2% EPA+DHA on a dry matter basis), as previously formulated for the same species (Vagner et al, 2014). The composition and FA content of the two experimental HH and LH diets are summarised in Vagner et al (2015). For each of these two diets, the fish in two tanks per experimental temperature were fed for at least 4 months (2% of biomass per day) to ensure a good incorporation of dietary lipids into their cell membranes (Vagner et al, 2007(Vagner et al, , 2014(Vagner et al, , 2015.…”

“…The underlying mechanisms governing the metabolic response observed by Vagner et al (2015) have never been explored, but they are key to further understanding and predicting fish responses to the nutritional and thermal challenges induced under climate change. In the present study, we hypothesised that temperature and HUFA food content affect fish metabolism through a modulation of cardiac function, which is key to supplying the required amount of oxygen and nutrients to tissues (Claireaux, 2005;Clark et al, 2005).…”