engleski

Mandibular arch development in Oncorhynchus mykiss from Croatia

Mandibular arch development in Oncorhynchus mykiss Walbaum, 1792, was studied under intensive rearing condition. Data on this aspect of fry development were presented for both, the day post hatching (DPH) and standard length (SL). The study was based on 14 samples, (5 individuals each) collected in the fish farm “ Gacka” . Materials were fixed in buffered formalin, cleared by trypsin and stained with alcian blue and alizarin red (DINGERCUS and UHLER, 1977). At the average SL 18 mm (10 DPH), all samples still have yolk sac and there were no bony elements in mandibular arch. The splanchnocranium were formed by ethmoid plate, cartilaginous palato-quadratus, Meckel’ s cartilage, and hyoid arch. As a response to functional demands, first sign of ossification process were noticed on premaxillaries (PMx) and dentaries (Dn). At the same time, average SL 18, 8 mm, the roof of splancnocranium was ossified. On average SL 18, 8-21, 2 mm ossification process was in rapid progress and expanded on whole PMx, rostral part of maxillaries (Mx) and whole Dn. Ossification of dermal bone in mandibular arch (PMx, Mx and Dn) were finished at average SL 22, 8 mm (19 DPH). Ossification of other mandibular arch elements (articularies (Art), quadratus (Qu), retroarticularies (RArt)) start at the same time (average SL 22, 8 mm), and it is finished in fry with 27, 8 mm SL (50 DPH). The first sign of teeth on Dn and PMx were noticed at average SL 21, 2 mm (17 DPH). Intensive ossification process starts at the same time when yolk sac start to disappear and first sign of food is present in digestive tract. Finally it can be concluded that process of ossification is strongly linked to transition from endogenous to exogenous feeding. Specific characters were not equally clear-cut in all samples examined, because they are very variable in SL according to DPH. In the smallest individuals at 20 DPH some characters were not form yet, and in the biggest one at 19 DPH the same characters were totally developed. For this reason SL is consider as more reliable parameter than DPH.

Oncorhynchus mykiss; mandibular arch; development; ossification

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