Page 5 - Castriota_alii_2014

CASTRIOTA ET AL.
800 W= 0.0001 TL3.372 o
R2 = 0.857
700 n=60
600
,....._500
co
"~"" 400
300
200
100
o icant correlation found between predator size and prey size
60 65 70 75 80 85 90 95 100
TL (cm, without filament)
Figure 7. - Length-weight relationship for Fistularia commersonii, aging behaviours when body size of bluespotted cornetfish
centrai Mediterranean Sea.
rized in table II. The majority of samples belonged to the
length class 75-85; in particular, 16 specimens (34.7%) were
included in age class 2 (TL = 75.77 ± 1.75 cm), 22 (47 .8%)
were aged as 3 year old (TL = 82.62 ± 4.29 cm) (Fig. 5)
and age class 4 was represented by 8 specimens (17 .4%)
(TL = 94.35 ± 9 .83 cm).
Growth
The parameters of von Bertalanffy growth curve fitted
to total lengths at age were estimateci as: TL.c = 102.39 cm,
k = 0.493 1 year-1, to = -0.5741 years (Fig. 6) . The theoreti-
cal asymptotic total length (TLo: = 102.39 cm) gave results
lower than the largest specimen (TL = 107.5 cm) caught
in this study. The value of the growth performance index
obtained for all individuals was: <P' = 3.7134.
The relationship between weight and length estimateci for
F. commersonii in the study area is expressed by the equa-
tion: W = 0.000 1 TL3372 with R2 = 0.857 (Fig. 7). This spe-
cies showed positive allometry since the value of b = 3.372
resulted highly significantly different from the value 3 .O, as
confirmed by Student's t-test (tss = 4 .133; p< 0.01) .
DISCUSSIO N
The present study provides new information on biology
and ecology of the invasive Lessepsian fish F. commersonii
from the centrai Mediterranean Sea. Since 77 specimens may
not be representative of the whole population and reffect a
first stage of range expansion, results should be considered
as preliminary data.
Diet analysis indicated that bluespotted cornetfish is
exclusively piscivorous in the study area, as found in other
Mediterranean areas (Corsini et al_, 2002; Bariche, 2007;
Psomadakis et al., 2009), although some authors observed a
secondary predation on crustaceans (Kalogirou et al., 2007;
Bariche et al., 2009). Predation on the clupeid Sardinella
Cybium 2014, 38(1)
Biologica/ date on Fistularia conunersonii
aurita, the sparid Boops boops and centracanthids indicates
the propensity of F. commersonii to catch pelagic species,
although benthic and nectobenthic fishes, such as labrids
and other sparids, are also well represented in its diet. Such
feeding behaviour follows the same pattern adopted by this
species in its native habitat (Takeuchi, 2009), where F. com-
mersonii shows a foraging activity mainly focused on two
types of prey fishes: reef fish that typically dwell on or near
substrata (e.g., Tripterygiidae, Labridae) and pelagic fish
that shoal in the water column (e.g., Clupeidae, Carangi-
dae). Prey fishes were mainly juveniles, as showed by their
size; only three species [S. aurita, Thalassoma pavo (Lin-
naeus, 1758) and Symphodus ocellatus (Forsskal, 1775)]
were also found at the adult stage. The wide array of prey
fish belonging to different habitats testifies to the high ffex-
ibility of F. commersonii in the choice of its prey. The signif-
suggests ontogenetic changes in the diet of F. commersonii,
as previously reported in the Aegean Sea and in southern
Japan (Kalogirou et al., 2007; Takeuchi, 2009). In particular,
these changes may be related to the diversification of for-
increases, due not only to the habitat types andanti-preda-
tory behaviours of prey fishes, but also to associative forag-
ing with con- or heterospecifics, which improves its foraging
success (Takeuchi, 2009).
The analysis of feeding habits in non-indigenous inva-
sive fish assumes particular importance in individuating
potential competition for food resources with native species,
which may be damaged by the presence of a new competi-
tar in the own trophic niche. This event may have effects on
the ecosystem equilibrium and also on human activities such
as fishery. Therefore, future studies should investigate this
aspect in order to understand which native fish populations
and fishery resources are affected by invasive species.
To date, we could not find any study dealing with blues-
potted cornetfish ageing in the literature. Fish of tropical
waters are difficult to age because they grow in constant
water temperature all year round and, consequently, the for-
mation of growth increments (i.e. annuii) is compromised
(Smith and Heemstra, 2003). However, our specimens col-
lected in Sicilian waters, where temperature varies season-
ally, should have been subjected to annual variation of faster
growth in summer and slower growth in winter, like hap-
pens to fish of temperate waters. As expected, the vertebrae
of these individuals displayed concentric marks (i.e. bands
or rings) that can be due to annual growth increments. By
means of vertebrae readings, we estimateci the age of F. com-
mersonii varying from 2 to 4 years within the size range of
examined specimens. The maximum totallength in the study
area was l 07.5 cm, corresponding to 4 years, although its
maximum size reported in literature (i.e. 160 cm totallength)
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