The first record of Northern pike (Esox lucius Linnaeus) in the Zrebar Lake of Marivan, Kurdistan, Iran: A preliminary observation and assessment of morphology, diet, reproduction and invasive threat

The Zrebar Lake is a most important natural freshwater Lake ecosystem in the Kurdistan Province, west of Iran.  Since Decembeer 2019, there has been reports of an unusual fish species sighting in the Zrebar Lake. This has led our efforts to set traps, capture and identify the species as Esox lucius Linnaeus. Consequently, we made further, field assessments and conducted biological study in the laboratory. The preliminary results showed that the captured E. lucius from Zrebar lake have in average a body weight of 630.3 ± 182.1 gr, total length of 418.4 ± 41.3 mm, and age of 2.7 ± 0.5 year. Further we observed that the number of eggs per gram in females was 171.9 ± 26.3 and females sexual maturation stage is 5.13 ± 0.35 years(lowest stage 5 and 6 at most) and sexual maturation stage of males is 2.5 ± 0.57 years (lowest stage 2 and 3 at most). According to the RLG index (0.98 ± 0.12) this fish has a carnivorous diet with observation of Carassius carassius (Crucian Carp), Squalius cephalus (Common Chub), Alburnus sp. (Bleaks) and frogs (adult) in their Gastrointestinal tract. . Based on these observed diets, this invasive fish can have a direct and indirect impact on the population of many aquatic species in particular fish and amphibians. Our first observation on the reproductive organs of the male and female specimens obtained showed that they have an established mature and reproductive population in Zaribar Lake. This means that if they enter the downstream freshwater systems they can pose a serious threat to native fish populations and overall freshwater ecosystem.