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Temperature, as an environmental factor, plays an important role in life of fishes. This study was conducted to investigate effects of temperature on body shape of swordtail (Xiphophorus hellerii) during the early development using geometric morphometrics. A total of 60 newly-born fries were reared in two temperature treatments (17 and 26°C) for two months. The left side of the specimens were then photographed, 16 landmarks were defined and digitized using the software tpsDig2 to extract the body shape data. The extracted data were superimposed using generalized procreates analysis, analyzed using the discriminant function analysis and Hoteling's T2. There was a significant difference between body shape of the specimens exposed to the temperature treatments with those experienced higher temperature had a deeper head at the level of the operculum, deeper body depth and caudal peduncle, and shorter tail length. The results indicated that temperature is an important environmental parameter impacting the body shape of green swordtail during the early developmental stage.

This study was conducted to survey the allometric growth pattern of the swordtail (Xiphophorus helleri) during early developmental stage under rearing conditions. For this purpose, the fries were sampled after birth up to 60 day after birth (DAB), their left sides were photographed and morphometric parameters, including total length, head length, tail length, trunk length, eye diameter, snout length, and body depth were measured. The newly hatched fries were 8.3 ± 0.431 and 12.58 ± 0.234 mm in TL on 1 and 60 DAB, respectively. The results revealed growth priorities of this species during the early developmental stages. Based on the results, this species born with developed jaws and eyes that capable them to take the food immediately after birth and increasing the size of the mouth afterward to take larger food item. The inflection points of the most body segments are occurred during 30-35 days after birth showing a late morphological change in compare to oviparous species. These morphological changes are associated to head and snout lengths may be related to changing in feeding habit of this species. In addition, positive growth pattern of tail length is occurred earlier on 7 DAB improving its swimming capability to avoid predators and catch preys.