Not sure of genus, but order could be Isopoda.

It’s possible if the genus is one of Tylos sp ?

Pictures 1 and 3 are probably Isopoda.

But picture 2 shows a parasitic copepod.

Probably a female of Caligus centrodonti (?)

Its species name is related to its parasitism on the fish Pagellus centrodontus.

Sorry : ERRATUM

I think Figures 1 and 3 are not isopods because the segmentation is not compliant. They are actually also copepods, like Peltidium sp. or neighbors.

Brylinski Jean-michel so it is belonging to Harpacticoid copepods ?

Yes, Harpacticoid copepods.

About systematic, you have to consult WoRMS in internet.

"World Register of Marine Species"

I agree with Brylinski Jean-michel concerning picture 2 which shows a parasitic copepod belonging to Caligidae family and to Genus Caligus.

Following

Clarification:

I agree with Brylinski Dr Jean-michel concerning picture 2 which shows a parasitic copepod belonging to Caligidae family and to Genus Caligus.

However, neither cephalothorax shape (suborbicular with narrow frontal plates and rather small lunules in C. centrodonti), nor that of genital complex nor uropods correspond to those of the species centrodonti.

Oum Kalthoum Ben Hassine since it is found in a gut content of fish, can i only use the genus because it may be hard to identify to species as many of this copepod have its body broke and lost ?

Yes, of course, you can use the denomination Caligus sp. which implies that you have could not identify the species.

The presence of this copepod in the gut of fish is curious and unusual because it is an ectoparasite (external parasite) which, depending on the species, attaches to fish body or gills.

The fish that you have examined may be cleaners fish that feed on parasites attached on the body or on the gills of other fish. If not, some species of the genus Caligus, which normally attach to the body of their host fish, may momentarily abandon their host and swim again nearby (I myself had the opportunity to observe this behavior during experimentation). It is at this time that they are ingested by other fish.

Could you give me the name of the fish species from which you collect this parasitic copepod in its gut? In this case, I would have a better understanding.