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Population dynamics of Ferosagitta ferox (Chaetognatha) was carried out in coastal waters of Khur-e-Mussa's Channel in Khuzestan Province, northwest Persian Gulf. Monthly samples were collected with 300km mesh size plankton net in oblique tow from near bottom to surface waters. In total, 7 species of Chaetognaths were identified belonging to 1 class (Sagittoidea), 1 order (Aphragmophora), 2 families (Sagittidae and Krohnittidae) and 4 genera (Aidanosagitta, Ferosagitta, Flaccisagitta and Krohnitta). The identified species included A. Bedford, A. neglecta, F. ferox, Flaccisagitta enflata, F. hexaptera, Krohnitta pacifica and one unknown species. Due to presence and excessive frequency of F. ferox in all samples, we focused on its population variation as an indicator of Chaetognatha. We determined length groups for adult individuals in 4-21mm range with 1mm increments. The year round presence of juvenile and small individuals showed the continuous reproduction of F. ferox with two considerable peaks in March and July. The evaluated recruitment indicated that the species has a low growth rate and a long life cycle.

During the project of "Stock assessment of mesopelagic resources with Acoustic method", the feeding of lantern fishes was studied and it was found out that they are specified zoophagous. The most abundant of their stomach contents contain Copepods and Ostracods and with less important, the other stomach contents were Brachyuran larvae, Tintinnids, polychaeta, chaetognatha, Appendicularia, Lamellibranchia, shrimp's larvae, different lchthioplankton, crustacean appendages, juvenile squids and some other unidentified zooplankton. The Diatoms (as a random food) were rarely found in their stomachs. Also, small and juvenile lantern fishes formed a part of their stomach contents and it proved the cannibalism behavior of this fish. This behavior occurs mostly during daytime but the main time of myctophid's feeding occurs during night time.