| Abstract |
In the present doctoral thesis, the external morphology of reared gilthead sea bream
(Sparus aurata) was studied. The examination took place during the on-growing period,
starting from the juvenile stage and up to the harvest size. During the study, fish with
normal phenotype and skeletal abnormalities were examined. Concerning the fish with
normal phenotype, the main goal was to correlate the most significant ontogenetic
stages (juvenile and adult stages), in order to determine early predictors of the
commercial size product quality from previous life stages. The skeletal abnormalities
that were examined were those of haemal lordosis and upper jaw deformities, which
have significant effect upon the external morphology. Main goal was to examine their
evolution throughout the on-growing period.
For the follow-up examination of both normal and deformed specimens, 1700
juveniles were pit-tagged, allowing the examination at an individual level. In order to
examine the evolution of the external morphology, four additional samplings took place
during the on-growing period (77, 282, 371, 434 dpt). The examination of the body
shape was conducted with the method of geometric morphometry on the digital photos
of the pit-tagged fish. For the evaluation of the haemal lordosis, X-ray examination was
conducted on juveniles (1 dpt) and adult (434 dpt) fish, additionally to the digital
photos.
The results showed that the body shape of normal sea bream continues to change
even after the juvenile stage. The ontogeny of the shape was discriminated in two
separated phases with an inflection point at 202 ± 1.7 mm SL (through relative warp
analysis). The first phase was characterized by rapid allometric growth, whereas the
second phase showed a plateau. The main morphological differences were observed at
the head region. These allometric changes during the first phase of the ontogeny were
the main reason for the low correlation between the juvenile and adult stage (r=0.35).
The individual examination revealed different allometric trajectory patterns, which in
some cases were aligned with the population allometric pattern.
This was the first time that recovery of haemal lordosis in reared sea bream
population was recorded. During the on-growing period the lordosis was reduced at a
rate of 49.1%. The individual examination showed that 43.6% of lordotic juveniles (1
dpt) presented normal external morphology at the end of the trial (434 dpt). The
radiographic examination at the end of the on-growing period revealed two different
cases of haemal lordosis recovery. Either there was partial to complete remodeling of
the vertebrae, or a counter-balanced kyphosis was developed prior to lordosis. The
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geometric morphometric analysis did not reveal significant differences between the fish
with recovered external morphology and fish with normal external morphology since
the beginning of the trial. Additionally, the geometric morphometry discriminated the
juveniles with the recovery potential from the juveniles that will remain lordotic,
revealing a new aspect for the evolution of skeletal abnormalities during the rearing
process.
However, not all skeletal abnormalities can recover. The results of the doctoral thesis
revealed that jaw abnormalities with deformed skeletal elements, do not recover during
the on-growing period. Moreover, a new morpho-anatomical abnormality was
observed. The main feature of that cranial abnormality was the presence of a severely
vertical profile. That specific morpho-anatomical abnormality seems not to have any
deformed skeletal elements. At the end of the on-growing period, that abnormality was
recovered in the 43.9% of the cases. Finally, the ontogenetic analysis of the specimens
with normal cranial morphology showed that the head region keeps changing during
the on-growing period. The ontogeny of the cranial morphology was discriminated in
two phases with an inflexion point at 103.9 mm SL. Throughout the whole period,
allometric growth was significantly high, but being higher during the first phase. Main
morphological differences between the juvenile and the adult stages concerned the head
size and the jaw position.
Both the results of ontogeny and those of skeletal deformities, revealed that sea
bream external morphology keeps changing during the on-growing period. So the repair
of skeletal deformities as well as the significant ontogenetic changes of the normal
specimen during, can be used as significant tools for the quality improvement of the
commercial size product, the enhancement of the selective breeding programs, but also
the expansion of knowledge that concerns the architect of body shape.
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