INSTM Bulletin : Marine and Freshwater Sciences

First record of Alopias superciliosus Lowe,1841 (Elasmobranchii: Alopiidae) in Tunisian water

Ichrak BOUZIDI — 2023-11-21

On July 2021, one specimens of Alopias superciliosus Lowe,1841 was captured as bycatch in Kelibia (Tunisia) at the following coordinate 36°30’740” N; 11°48’451” E, by a trawler at 400 m depth. It was a mature male of 350 cm total length and 159 kg in eviscerated weight. This represents the first record of the bigeye thresher shark in the area.

First Record of the tropical seagrass Halophila stipulacea (Forsskål) Ascherson, 1867 in the Punic Port of Carthage-Salammbô (Northern Tunisia)

Karim BEN MUSTAPHA — 2023-11-30

The bioinvasion has increased in recent years with climate change, and some invasive species have caused significant damage to the marine ecosystem, including a great loss of biodiversity. The studied seagrass is a marine tropical phanerogam introduced in the Mediterranean at the end of the 19^th century and in southern Tunisia in 2003. In this study we record this species for the first time in northern Tunisia, precisely in the Punic Port of Carthage-Salammbo. Surveys were carried out on foot around the Punic Port, and measurements/photos were taken on site, and others in the laboratory on taken samples. Most of these measures do not differ from those carried out elsewhere in the Mediterranean. For the moment, the plant does not occupy a large part of the port buttom, but it may invade all the area in the future.

A rare stranding event of the short beaked common dolphin (Delphinus delphis) in the eastern Tunisian coastline

Olfa CHAIEB — 2023-12-07

A short beaked common dolphin was found stranded on March 3rd 2021, on Hammamet beach (Central-eastern Tunisia). This is a rare stranding event since it represents the third documented stranded individual reported on Tunisian coastline for half a century. Necropsy of the freshly dead female dolphin was conducted to know the presumable cause of death. The pregnant dolphin was bearing a mid-term female fetus with fully developed organs. Detailed biometric data were taken for both individuals. Samples were collected and preserved in the tissue bank of the national stranding network. The freshly dead fetus is preserved at the oceanographic museum for scientific collection. The rare stranding of this species observed here would be attributed to the small population frequenting Tunisian waters. This note improves knowledge on this poorly studied species in the south-central Mediterranean area.

Effects of chitosan-microparticles-coating on the quality of vacuum-packed sea bass (Dicentrarchus labrax) fillets during refrigerated storage

Nadia BESBES — 2023-03-13

In this work, a combination of vaccum pachaging and bio-coating by chitosan were used to coat sea bass (Dicentrarchus labrax) fillets in order to delay growth of total mesophilic aerobic bacteria, psychrophilic bacteria during refrigerated storage (22 days).

The preservative effect of refrigerated and vacuum-packed seabass (Dicentrarchus labrax) fillets treated at two different percentage doses (0.2% and 0.5% w/w) of co-products of shellfish was evaluated on the basis of microbiological, proximate composition, pH, total volatile basic nitrogen (TVB-N), trimethylamine (TMA), thiobarbyturic acid (TBArs), and fatty acids (FA). Two ways ANOVA and multiple comparisons were applied, factors being storage time and treatment. During refrigerated storage, the treatment with chitosan from separate co-products exhibited more antimicrobial activity and the lowest value of the TVB-N, TMA and TBArs compared to control lots. The bio-coating by 0.5% dose of chitosan preserved quality and the prolonged shelf-life for 10 days longer.

Overall, this treatment may open new promising opportunities for the biopreservation of fish products by enhancing the period of storage of refrigerated and vacuum-packed seabass fillets.

Comparative study on the composition and functional properties of chitin/chitosan extracted by new combined bioprocess

Boutheina BESSADOK — 2023-04-03

Bio-extraction of chitin is a greener and eco-friendly process than the conventional chemical method. Taking shrimp waste of Pandalus borealis recovered from plant as a model, two methods were applied for chitin extraction; a chemical and a yeast-based processes (Ch-C and Ch-B respectively). The recovered chitins and chitosan were tested for their biochemical and functional properties. Compared to commercial chitin, both lots, have similar chitin recovery (~26%) and physiochemical properties with ash<1%, protein <10%, with degrees of acetylation (DA) varying 70-80%. However, chitosan obtained from Ch-B lot showed significantly lower molecular weight (MW) and DA (MW: 6.34 KDa, DA: 23.4%) than that found in Ch-C chitosan (MW: 11.36 KDa, DA: 33.4%). The new method proved to be efficient for the production of chitosan of good quality which allowed the elaboration of the membrane.

Overview of Bottlenose dolphin depredation in Teboulba region (East of Tunisia)

Rimel BENMESSAOUD — 2023-04-04

This work was carried out in response to the numerous fishermen claims following to the interaction between dolphins and fishing gears along the coast of Teboulba. The aims of this work were: to establish an inventory of dolphins present in the study area and interacting with fisheries, to define the most affected fisheries by the depredation and to attempt to assess it economic consequences.

For this purpose, field surveys as well as weekly monitoring of a sample of the fleet and sea trips were carried out in order to respond to the previously mentioned objectives.

The findings of this study led to the conclusion that there are two dolphin’s species: the Bottlenose dolphin and the Striped dolphin. These two species have a different demographic and ecological distribution. They also interact in two different ways with the fishing boats and their nets. According to the surveys, the most depredated fisheries is the small scall fisheries. Set gillnet and trammel nets were the types of the fishing gear most vulnerable to dolphin depredation. The depredation rate and economical loss due to depredation vary slightly between gillnets and trammel nets. The depredation induces many holes with different size requiring mending operations that can be onerous. Likewise for landing, the resulting bites on the catch leave it unsaleable. It is necessary to continue this study in order to identify the factors that can cause the depredation and propose mitigation measures to avoid any ecological and economic blunder.

Eroding coastal sandy barriers under changing aeolian flux in the Gulf of Tunis

Oula AMROUNI — 2023-08-28

Sandy barriers are coastal features formed and reworked by terrestrial and marine-induced processes along decadal to millenary scale periods. In the semi-arid areas along the extended North African coast, these coastal landscapes are undergoing accelerated morphodynamical changes induced by intensifying anthropogenic and climate drivers in the last century. To quantify the latter, we assess the changes in sediment dynamics of the Ghar El Melh sandy barrier extended over the northern part of the Gulf of Tunis in Tunisia using sedimentological analysis and quantification of the aeolian flux. A total of 37 subsurface samples and 30 surface aeolian trapped ones were collected at the coastal dunes of Ghar El Melh. Our sedimentological analysis reveals a distribution of 97% of sandy sediments and 3% of silty facies. The modal statistical analysis suggests that there are three distinguishable sediment types with 87% of samples formed by fine sands with modal value of 0.16 mm. The mixture of these indicates mixed terrigenous and marine sources redistributed by the hydrodynamic processes. The measurement of the aeolian flow suggests a maximum value of 0.0022 kg.m.-1min-1 which occurs in dust storms. This study reveals the low detrital sand supplies to the lagoon-sea barrier of Ghar El Melh, results in its gradual submersion, further exposing the coastal lagoon and engendering severe ecological degradations.

Striped red mullet (Mullus surmuletus, Linnaeus, 1758) from Rafraf - Sidi Ali Mekki region (Bizerte): length-weight relationship and histological assessment of gonad maturation

Raouf DHAOUADI — 2023-11-02

The aim of this study is to investigate the gonadal changes of striped red mullet (Mullus surmuletus Linnaeus, 1758) in Rafraf – Sidi Ali Mekki region in Tunisia. A total of 243 specimens were collected monthly between March 2014 and February 2015. Fulton’s condition factor (K) and the length-weight parameters were estimated. There was correlation between the fish total length and weight (R²: 0.75). The K values ranged between 0.93 and 3.38. The values of b parameter ranged from 3.18. Goandosomatic and hepatosomatic index show maximum values during April. Different stages in females and in males were observed according to gonadal development.

Seasonal variation of ectoparasite infestation levels of Trachurus picturatus in Bizerte (Tunisia)

Ilhem HAMDI — 2023-11-02

The blue jack mackerel, Trachurus picturatus, is a commercially important resource in the Mediterranean Sea and the North-East Atlantic. The main aim of this work was to assess the infection levels and diversity of the ectoparasites of the blue jack mackerel. Over a one-year period, between March 2017 and February 2018, 126 specimens of T. picturatus were collected seasonally from the Bizerte coast (Tunisia). The ectoparasite fauna of the examined host was composed of the two monogenean species, Pseudaxine trachuri and Gastrocotyle trachuri and a copepod species, Peniculus fistula fistula. This is the first record of this copepod parasite in Tunisia.

The analysis revealed that the infection levels fluctuated throughout the year. Both monogeneans (P. trachuri and G. trachuri) had high prevalences during the warm season (P% = 87.1, P% = 32.3, respectively).

Additionally, P. trachuri showed some seasonal variations in mean abundance and mean intensity between summer and the other seasons. Furthermore, there was a highly significant variation in the mean abundance of G. trachuri between the summer and autumn-winter seasons. The results of the current study may be explained by the seasonal variations in environmental conditions, the life cycles of the hosts and parasites, the feeding and migratory patterns of the hosts, the chemicals released by the hosts, and the interspecific competition between the two monogenean species.

Preliminary inventory of metazoan parasites of the Lessepsian bluespotted cornetfish Fistularia commersonii in the Gulf of Gabès, Tunisia

Wiem BOUSSELLAA — 2023-11-23

Biological invasions are widely acknowledged as a serious threat to biodiversity, but the role of parasites in marine ecosystem processes is still poorly understood. The so-called Lessepsian migration, or invasions through the Suez Canal from the Red Sea to the Mediterranean Sea, also fits this description. Here, we studied the parasitofauna of Fistularia commersonii collected from the Gulf of Gabès of Tunisia. 43 individuals of F. commersonii were sampled from the Gulf of Gabès. Parasite richness, prevalence and intensity were investigated, Additionally, we reviewed the literature to identify native and invasive parasite species recorded. Our results suggest the co-introduction of nine parasite species that are assumed to be originate from the Red Sea. In addition, we found that the invasive fish has acquired nineteen parasite species that are native from the Mediterranean Sea. The Lessepsian migrant may potentially change the dynamics of native and invasive parasite-host interactions through parasite co-introduction and parasite acquisition, according to these results. The higher F. commersonii infection rates in the area that has been invaded are also consistent with the predictions made by the "Enemy Release Hypothesis." These results show the importance of using community studies, such as the one described here, to understand the role of parasites in Lessepsian migration.

Acute and subacute toxicity of naphthalene in a filter-feeding species Styela plicata (Chordata, Ascidiacea)

Tahani EL AYARI — 2023-11-29

The aim of the current study was the assessment of a Polycyclic aromatic hydrocarbon (PAHs) toxicity on an ascidian species, Styela plicata. Acute and subacute toxicity of naphthalene (NAP) has been determined using five increasing concentrations (0.5, 1, 1.5, 2.5 and 5 mg/l) during 96h of exposure. The half lethal concentration (LC50, 96h) value of naphthalene for S. plicata was 2.41 mg/l. Furthermore, the filtration activity decreased in the five tested concentrations of NAP; a significant decrease by 69% and 91.8% was observed after 1h in the groups exposed to C1 and C5, respectively. A similar pattern was noted after 2h of filtration; the decrease was estimated to 39% in C1 and 72.5% in C5. The results from this bioassay confirmed the toxicity of NAP on S. plicata; we also provided information about the use of S. plicata as a potential bioindicator species for the assessment of PAHs toxicity.