Optimizing the Timeframe to Produce Polychaetes (Hediste diversicolor) Enriched With Essential Fatty Acids Under Different Combinations of Temperature and Salinity

Abstract

Polychaetes can be successfully employed to recover essential fatty acids (EFA) from wasted uneaten aquafeeds present in aquaculture effluents. The optimization of the timeframe required to produce premium ragworms (Hediste diversicolor) biomass rich in EFA is paramount to make available to the aquafeeds industry another alternative ingredient to fish meal and fish oil. The present study aimed to evaluate the potential enrichment of ragworms fatty acid (FA) profile when fed a commercial aquafeed during 10, 20, and 40 days (D10, D20, and D40) under different combinations of water temperature (20 and 25°C) and salinity (15, 20, and 25). Total FA incremented progressively overtime, with D40 polychaetes exhibiting average values ranging between 70 and 90 μg mg–1 DW. The average values of n-6 FA ranged between 13 and 17 μg mg–1 DW, while that of n-3 FA varied between 17 and 19 μg mg–1 DW at D40. No significant differences were found in the FA profile of H. diversicolor cultured under different combinations of temperature and salinity. The FA profile of cultured polychaetes exhibited between 28 and 31% dissimilarity from that of wild conspecifics and displayed a higher content of two essential n-3 FA: eicosapentaenoic (20:5 n-3, EPA) and docosahexaenoic acids (22:6 n-3, DHA) (values ranging between 9.6–11.2% and 4.3–5.0% of total FA, respectively). A higher similarity in FA profile was recorded between D40 polychaetes and aquafeed than with initially stocked or wild specimens. Palmitic (16:0), oleic (18:1 n-9), linoleic (18:2 n-6), eicosadienoic (20:2 n-6), EPA (20:5 n-3), and DHA (22:6 n-3) were the FA whose concentration exhibited the highest increment. Evidence of de novo FA biosynthesis was observed through the formation of some FA that were neither present in the initially stocked biomass, nor in the aquafeed supplied, such as 5,11-eicosadienoate (Δ5,1120:2), 7,13,16-docosatrienoate (Δ7,13,1622:3), dihomo-gamma-linolenic (20:3 n-6), eicosatrienoic (20:3 n-3) and eicosatetraenoic (20:4 n-3) acids. A plateau of total FA, n-6, and n-3 FA was not reached over the study period. Overall, the present study highlights the potential of H. diversicolor as an extractive species for integrated multi-trophic aquaculture (IMTA) applications.

Biochemical composition of Hediste diversicolor (OF Müller, 1776) (Annelida: Nereidae) reared on different types of aquaculture sludge

“…Differences in proportion of EPA, DHA, and linoleic acid in the two diets were reflected in the polychaetes. Moreover, we saw a relative decrease in SAFAs with increasing feed level in both diet groups which corresponded to a relative increase in MUFAs for polychaetes fed smolt sludge and a relative increase in PUFAs for post-smolt-fed polychaetes, suggesting a selective enrichment and a shift of the FA profile towards a higher proportion of unsaturated FAs by H. diversicolor with increased feed supply as described in previous studies (Garcıá-Alonso et al, 2008;Kabeya et al, 2020;Jerońimo et al, 2021).…”

Evaluating the Bioremediation Capacity of the Polychaete Perinereis gualpensis (Jeldes, 1963) for Atlantic Salmon Aquaculture Sludge

“…Arenicola marina reported similar survival (93%) after being fed with fish waste during 55 days at a density of 150 organisms m −2 [63]. However, other studies with H. diversicolor reported lower survival (38-54%) when fed during 40 days with commercial fish feed at the same density used in this study (300 organisms m −2 ) [49]. Additionally, lower survival (50-70%) was achieved by P. nuntia vallata fed on Japanese flounder sludge after 35 days of trials [28].…”

“…These units consisted of plastic containers with a volume of 68 L. A total of 9 units were used (3 per treatment). The density was set in all treatments at 300 organisms m −2 , a level at which other polychaete species exhibited higher feed intake, growth, and survival rates compared to higher densities (400, 600, 1000, and 3000 organisms m −2 ) [22,34,[47][48][49].…”

“…High densities cause depletion in feeding, competition, and cannibalism in other species of polychaetes [47,48,68,69]. Densities higher than 1000 organisms m −2 were reported to cause aggressive behaviour and lower survival, growth rates, and food consumption rates in H. diversicolor [34,49]. For P. aibuhitensis, these effects occur at densities higher than 400 organisms m −2 , being recommended to apply 200 organisms m −2 [22].…”

Influence of Body Weight and Water Temperature on Growth in Ragworm Hediste diversicolor

“…To achieve the best growth and reproductive control (preventing or facilitating), key environmental variables, such as temperature and photoperiod, must be managed correctly [7,16]. Diet composition can also play a key role; a diet low in lipids can slow down early maturation in HD [15,36], while a diet high in protein content can initiate earlier gametogenesis processes and earlier sexual maturity stages [22,37]. Using fish feed to rear HD is standard practice under experimental conditions.…”