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Slovenia, National Institute of Biology – Marine Biology Station Piran

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Abstract Bachelor Project FBT 2018-2019: Analysis of jellyfish mucus composition for biotechnical application

This bachelor project is a part of GoJelly project, a Horizon 2020 project, that deals with using jellyfish biomass for product development. Jellyfish produce mucus and it has been shown that mucus has the so-called sticky properties that allow micro and nanoplastic particles to be adsorbed. One of GoJelly's main and ideal goals is to produce a biofilter prototype that would enable the collection of microplastics from wastewater treatment plants (“GoJelly”, 2018).

In order to realise this product development with jellyfish mucus, biochemical composition between mucus extracted from different species were examined as well as the physico-chemical stability. Besides that, jellyfish mucus characteristic of capturing microparticles from surrounding seawater was examined. This was important to see if the mucus can be used as a biofilter.

The mucus produced by jellyfish is highly heterogeneous and that makes consistent subsampling difficult. To address this problem, four treatments are applied on the mucus. When analysing the biochemical compounds on the mucus, treated mucus -more specific treatment 4- gives more representative results and has therefore more homogeneous mucus.

Harvesting jellyfish, the laboratory mucus extraction step and the preservation can take a long time. Also, as mucus is rich in proteins, bacteria start to degrade it fast. In order to minimize that, stability experiments were performed. The mucus was stored in the freezer (-20 °C) and replaced after a certain time to -80 °C because bacterial activity is then completely stopped.

This is applied to see if the mucus is still chemically stable after a certain time in the freezer. After the stability experiments, the mucus was analysed for different biochemical compounds. The results show that the chemical composition of the mucus is stable after several days/weeks in the freezer.

The biochemical composition of the mucus from different species shows that in general more proteins are present in the mucus then carbohydrates and the amount of lipids in the mucus is negligible. The amount of carbohydrates, proteins and lipids in the mucus is different between species, but it is shown that the amounts are approximately the same per individual of the same species.

The microparticle analysis shows that not all mucus that is produced by jellyfish is able to capture microparticles (MP) quantitatively because not all mucus has the same physico-chemical properties needed to adsorb MP efficiently. Further analysis need to be performed to see if jellyfish mucus has potential to be used in the product development of the biofilter.

The mucus stability experiments showed that mucus is still chemically stable after storage in the freezer (-20 °C) for several days/weeks, but the microparticle analysis showed that mucus loses the hydrogel structure and adsorptive characteristics when stored in the freezer (-20 °C) for several weeks. The analysis also showed that there is a breaking point of the maximum amount of MP that can be captured by the mucus between the concentration of 8 x 105 MP/L and 1,0 x 106 MP/L, but this needs to be tested further.

Samenvatting eindwerk 2011-2012: Impact of fish farming and seasons on the feeding ecology of commercial fish in the Portorož Fisheries Reserve
The main aim of this project is to evaluate the impact of fish farming on wild, common and economical relevant fish species – Dicetrarchus labrax, Liza aurata, Sparus aurata, Pagellus eryhtrinus and Lithognathus mormyrus - in the Northren Adriatic Sea, more specifically in the Portoroz Fisheries Reserve. In this fisheries reserve a fish farm is located, which not only offer shelter for the wild fish with its several hanging cages. The wild fish also can get additional food in the form of the remaining pellets passing through the cages or from other organisms such as fouling on cages or animals inhabiting the sediment in this more eutrophic ecosystem.
The feeding habits of this five fish species will be analyzed by studying the stomach content of these fish. Also the surrounding area and the seasons will be taken into account in this project.  
The samples were taken on two locations, one near the fish farm and a control which is 500m away from the fish farm, but still in the fishery reserve. This last location is used as control for the first one. After catching, measuring and weighting the fish the stomach is taken out and cleaned. The content of the fish stomach is cleaned over three sieves of different sizes (1000µm, 500µm and 250µm), collected and stored – together with a dye (Rose Benghal) that colors animals, specifically their proteins – for further research. Also the stomach weight and fullness is determined. The stomach contents is analyzed for the presence and abundance of macro- and meiofauna using microscopy. The macro- and meiofaunal organisms are determined and counted. The last step of this project is putting all the received data in a database and doing some statistical processing  to be able to make conclusions about the diet of the fish and about the prey organisms consumed by the different fish species on the different locations in the different seasons.
In general more fish were caught in summer than in winter and more fish were caught near the fish farm than in the control station. Liza aurata seems to be the most important fish in this area and was most caught in summer near the fish farm. For Dicentrarchus labrax, Lithogathus mormyrus and Liza aurata all the samples were indicated as full and the average wet weight of the stomach content was the highest for Dicentrarchus labrax.
Regarding the consumption of prey items of different size crustaceans were, next to worms, quite an important food item. Molluscs only appear in samples from Liza aurata, Pagellus erythrinus and Sparus aurata and were more eaten in summer. Other fish were also an important food item, because tissue and other things that give the impression that the fish ate another fish, were found in all the fish species and almost for all the mesh sizes. In general can be concluded that Dicentrarchus labrax and Liza aurata prefer bigger prey items than the other fish species. But Liza aurata caught in winter near the fish farm ate only small prey items, only meiofauna. The other three fish species are quite comparable with each other regarding the size of the consumed prey items.
Food items like tissue, from other eaten fish, nematodes and pieces of gill sled form Branchiostoma lanceolatum were found in all the five fish species in a high frequency.
Concerning the variability of ingested items all the five fish species have a varied diet and Liza aurata has the most varied diet. A difference between the two season is not found for the diet of different the fish species, only in winter the diet was sometimes less extensive. A difference between the two stations is only found for Pagellus erythrinus. Near the fish farm Pagellus erythrinus fed mostly on gastropods, in the control station this fish had a more varied diet.
Not only macro- and meiofauna were found in the stomach content, also fish pellets and abiotic structures like pieces of plastic and glass were found. The fish pellets were only found in samples from Dicentrarchus labrax and Lithogathus mormyrus, near the fish farm and in both seasons. Because the fish bread in the fish farm are also Dicentrarchus labrax, maybe some fish escaped from the fish farm. This is not sure and should be more investigated in the future, but when fish pellets where found in the stomach content, the stomach mostly only contained fish pellets. The abiotic structures were only found in a few samples and only in samples from Dicentrarchus labrax, Pagellus erythrinus and Sparus aurata. Regarding to the pollution of the sea, this discovery is quite important, but also for this more research is needed. A last special ingested item are parasites. Parasites are only found in summer and there is no big difference between the different stations. The founded parasites are trematodes and some hookworms like Acanthocephala. Also nematodes can be parasitic but due to the fact that the difference between parasitic and non-parasitic nematodes is difficult all the nematodes were counted as prey items.
In general can be concluded that the most fish were caught in summer near the fish farm and that Liza aurata is a quite important fish species for this area. In general the fish farm do not have a big effect on the diet of the investigated fish species, only for one fish species a difference between the two stations was found. Due to the fact that none of the fish species were caught in every season in the bot stations a general conclusion about the effect of the fish farm on the wild fish species cannot be made up. Therefore more research is needed.




Traineeship supervisor
Mateja Grego
Traineeship supervisor
Katja Klun
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