Effects of rearing density on growth, fatty acid profile and bioremediation ability of polychaeteNereis diversicolorin an integrated aquaculture system with rainbow trout (Oncorhynchus mykiss)

Abstract

The objective of this study was to assess the effects of rearing density on the growth and fatty acid profile of Nereis diversicolor and on its capability to bioremediate wastewater in an integrated culture system with rainbow trout (Oncorhynchus mykiss). To this end, a batch of juvenile N. diversicolor (0.03 ± 0.01 mg) was assigned into four different densities (T 1 = 250, T 2 = 500, T 3 = 1,000, T 4 = 2,000, besides T 0 = with no worm) in three replicates. The worm groups were fed with solid waste that was supplied from tanks containing rainbow trout (107.17 ± 13.5 g;1.39 ± 0.18 kg/m 3 ). During the experiment (60 days), the water temperature was 17.71 ± 0.6°C. The results revealed that SR%, SGR% and WG% of N. diversicolor in T 1 were significantly higher than those of T 2 , T 3 and T 4 . Both FER rate and biomass gain in T 4 were significantly higher than those in the other groups. The highest removal rate of NO 2 -N (73.72%), NH 3 -N (65.70%), PO 4 -P (59.32%), BOD 5 (69.60%) and TSS (82.33%) were observed in T 4 . The major fatty acids presents were palmitic acid, oleic acid, linoleic acid, stearic acid and alpha-linolenic acid in all worm-treated groups, with no difference observed in the concentration of these fatty acids among them. Taken together, these findings suggest that organic wastes from rainbow trout farms could be recycled to achieve a sustainable aquaculture goal, and demonstrate that a high percentage of fatty acids in fish feed is not absorbed by rainbow trout but is done by N. diversicolor. K E Y W O R D Sbioremediation, fatty acid profile, integrated aquaculture, Nereis diversicolor, Oncorhynchus mykiss

Potential of the polychaete Hediste diversicolor fed on aquaculture and biogas side streams as an aquaculture food source

“…H. diversicolor has been shown to grow well on aquaculture side streams (Pajand et al 2017, Marques et al 2018, Wang et al 2019, Yousefi-Garakouei et al 2019. By diverting some of the fish sludge used for biogasification to polychaete production, and combining this with solid biogas digestate (SBD) to serve as a feed source for the polychaete worms could add to the value of both wastes.…”

Recovering wasted nutrients from shrimp farming through the combined culture of polychaetes and halophytes

“…The OM in the top 20 and 20-100 mm substratum depth was reported between 0.2-0.4% LOI and no differences were verified in IMTA designs stocked with A. marina and H. diversicolor. Polychaete assisted sand filters are highly efficient in the retention of POM which is incorporated into valuable extractive worm biomass 11,[39][40][41][42] . A very important role was played by the sand bed of PASFs by retaining and keeping OM available to sustain the growth of polychaetes, while these organisms promoted bioturbation (sediment re-working and bio-irrigation, which enables dissolved oxygen to reach deeper layers of the substratum), a feature which is paramount to avoid the clogging of the system and maintain the percolation of water through the sand bed 39 .…”

Performance of polychaete assisted sand filters under contrasting nutrient loads in an integrated multi-trophic aquaculture (IMTA) system

“…In marine land-based production, the recovery of valuable nutrients present in effluent waters can be pursued through the integration of extractive species capable of recovering available POM. Marine polychaetes have been often pinpointed as holding great potential to recover wasted nutrients from POM with species such as Hediste diversicolor 9 , 20 – 25 , Perinereis aibuhitensis 26 , Alitta virens 26 , 27 , Perinereis nuntia 28 , 29 , Perinereis helleri 29 , 30 , Arenicola marina 26 , Abarenicola pusilla 31 , 32 , Capitella sp. and Ophryotrocha craigsmithi 33 already being tested under IMTA designs.…”

“…The ragworm, Hediste diversicolor (O.F. Müller, 1776), has been a key species to include in IMTA models, as it allows the recovery of otherwise wasted nutrients in the form of a biomass rich in highly unsaturated fatty acids (HUFAs), namely eicosapentaenoic (EPA, 20:5 n − 3), docosahexaenoic (DHA, 22:6 n − 3) and arachidonic (ARA, 20:4 n − 6) 20 – 25 . The ability of this species to synthesise de novo polyunsaturated fatty acids (PUFAs) and HUFAs 34 is an important feature when selecting the different trophic compartments that will be included in an IMTA design.…”

“…Polychaete assisted sand filters (PASFs), are sand column filters stocked with marine worms that are highly efficient in the recovery of POM in the form of these species biomass 9 , 20 , 21 , 29 , 30 . By fostering the retention of POM and contributing to its mineralization, thus enhancing the availability of dissolved inorganic nutrients, PASFs can play a key role in IMTA designs including macro/micro algae and/or halophytes, if integrated as the first extractive unit 9 , 23 .…”