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Journal of Agricultural Science and Technology A and B
& Hue University Journal of Science 5 (2015) 548-560
doi: 10.17265/2161-6256/2015.12.014
Biological Features and Distribution of Giant Trevally
(Caranx ignobilis Forsskal, 1775) in Tam Giang-Cau Hai
Lagoon Systems, Vietnam
Tran Vinh Phuong1, Hoang Thi Van Anh2, Le Thi Nhu Phuong3 and Nguyen Quang Linh1
1. Center for Incubation and Technology Transfer, Hue University, 07 Ha Noi Street, Hue City 47000, Vietnam
2. Faculty of Fisheries, College of Agriculture and Forestry, Hue University, 102 Phung Hung Street, Hue City 47000, Vietnam
3. Faculty of Pre-School Pedagogy, Ha Long University, 58 Nguyen Van Cu, Ha Long City, Quang Ninh 20000, Vietnam
Abstract: The study aimed to investigate biological characteristics and distribution of a new fish species Giant trevally (Caranx
iginoblis) in Tam Giang-Cau Hai lagoon systems and preliminarily discover the reproductive abilities of a migration species from sea
into lagoon. Results showed that the species appeared in the lagoon since 2005 and farmers started raising by cages at Tu Hien
estuary and Loc Binh area for well-growing and a best market to consumers. There were distributed of the fingerlings from sea into
lagoon from October to December through inlets, so fishermen can collect every year by bottom nets and enclosed net. Fish heads are
growing a faster than other species, but not sustainable development of the culture model. Besides, wild fish also can be collected by
fishmen at inlets with the bigger of averaged body weight 1.99 ± 1.22 kg and length 45.66 ± 17.56 cm. The species are big mouth and
contained sharp teeth. There are flat body and head length, pectoral fin rays, dorsal and anal yellow, gray dorsal, and ventral surface
is silver white. They adapted in water environmental conditions of pH (7.1-8.5), dissolved oxygen (DO) (2.7-4.5 mg/L), salinity
(17.0‰-33.3‰) and temperatures (16.8-32.5 °C). The reproductive performance of 50 fish samples, which were detected on mature
female fish and male fish for eggs or spermatorrhoea, respectively, was investigated. Results of slices on gonads in stages I, II and III
showed that the germplasm is a special source of valuable genes of the species and local aquatic resources.
Key words: Giant trevally, lagoon, biological features, distribution, characteristics.
1. Introduction
Tam Giang-Cau Hai has more than 22,000 ha area
with many aquatic species and it is also good for
fishing opportunities. Giant trevally (Caranx iginoblis)
migrate and live in the lagoon, and fishing men can
obtain the wild fish species from Cau Hai area and Tu
Hien estuary to culture in the fish-cages and thus to
have a good result and economic income. This fish is
a natural source of a new species to live in the lagoon
since 2005 through Tu Hien estuary, with a high
commercial value of price and well-adapted to salinity
changes from sea water to brackish water. The fish
have a faster growth rate than other species at the fish
Corresponding author: Tran Vinh Phuong, Ph.D., research
field: gene resource conservation.
cages. Giant trevally is the concern of many fishermen
and communities to collect the fingerlings for
aquaculture, but the seed source are limited and
usually just drift in the estuaries in a short time
(October to March) in rainy condition. Farmers and
scientists would like to determine age and growth rate
of this species, and they can have understand more
biological characteristics, specially migrations,
distributions and growth, mature in life cycle. The fish
age study was conducted by scales, but forever soles
at the 20th Century, the study about age and growth of
new fish has many achievements recorded [1-3]. This
was also the first case to have demonstrated in
scientific and technological application for locations
for backward water condition.
Due to requirement of scientific studies, the
D
DAVID PUBLISHING
Biological Features and Distribution of Giant Trevally (Caranx ignobilis Forsskal, 1775)
in Tam Giang-Cau Hai Lagoon Systems, Vietnam
549
investigate trends on the biological characteristics and
reproductive performance have been focused on, such
as embryonic and gonad development, the level for
gonad maturity, fecundity, hatchering and spawning
conditions. Reproductive activity is closely related to
various processes, such as growth, nutrition and
feeding assurance. Study on the significant
combination of theoretical and practical aspects at the
same times contributes to exploit, protect and use
resources appropriately [4-6]. The research aimed at
investigation of biological characteristics and
distribution of a new fish species with potential for
cage culture in Tam Giang-Cau Hai lagoon
systems, as well as preliminarily discovering the
reproductive abilities of a migration species from sea
into lagoon.
2. Materials and Methods
2.1 Materials
All specimens of giant trevally (Caranx ignobilis
Forsskal, 1775) (Fig. 1) were collected at Thua Thien
Hue coastal region, especially in Tam Giang-Cau Hai
lagoon system from 2014 to 2015.
2.2 Methods of Collecting Information and Samples
The survey collected information via questionnaires
to fishermen and farmers at Loc Binh, Vinh Hien and
Hai Duong, Tam Giang-Cau Hai lagoon systems.
Samples have been collected in wild and cage
conditions. Morphologically samples must be intact
form and shape in formaldehyde 5% enclosed with the
label, and the local name, date and place of sampling
are post outside sample bottles.
2.3 Biological Variables
The study of biological characteristics of fish giant
trevally includes a morphological characteristics,
growth variables, nutritional feeding characterizes and
reproductive characteristics.
2.3.1 Morphological Characteristics
Morphological characteristics can be discovered by
observation in fields and labs and based on the
classification criteria from Figs. 1 and 2.
2.3.2 Growth Variables
The intercept (a) and slope (b) of regression line
were calculated by using the following Eq. (1)
according to Berverton-Holt (1956) updated by Ref.
[3]:
W = a Lb (1)
where, W = body weight (g) and L = body length (cm).
The age of fish was identified by scales. The fish
Giant trevally with flakes are soaked in 4% NaOH
solution to remove grease, dirt or pigment clinging on
flakes. Cash observations of opaque concentric rings,
contiguous rings throughout the fish on the scales and
the boundary between the opaque regions allow us to
identify individuals within the age in years. Directly
observe using microscopy by eyes, and estimate fish
age according to Nikolsky updated by Ref. [3].
2.3.3 Nutritional Feeding Characterizes
Feed was removed from the intestine and stomach
for specimens and then observed under a microscope
or magnifying glass binocular. Use keywords to
classify low level plants, invertebrate aquatic, as “the
kind of invertebrate” of the classification of marine
planktonic algae silicon [3], identification of the
invertebrate groups freshwater common in Vietnam.
The coefficient of fat fish was calculated using Eqs. (2)
and (3) according to Fulton (1902) and Clark (1928),
updated by Ref. [3]:
3×100
W
QL
(Fulton) (2)
0
3×100
W
Q
L
(Clark) (3)
where, Q = fat parameter, W = body weight and L =
body length.
Fat is accumulated in the fish and the fat fish can
only be pinpointed with the fat accumulation into
belly and fat layers. Additionally, when conducting
anatomical fresh fish, the simple method can be used
to determine fat under five levels by Prozovxkaia, M.
L. (1957) updated by Ref. [3].
Biological Features and Distribution of Giant Trevally (Caranx ignobilis Forsskal, 1775)
in Tam Giang-Cau Hai Lagoon Systems, Vietnam
550
2.3.4 Preliminary Reproductive Characteristics
Fish samples were obtained at surgery tables and then
determined the volume of the maturity stages and
gonadal morphology under six ladder levels according
by Kiselevits, K. A. (1923) updated by Ref. [3], and then
fixed in Bouin solution which composed of picric acid,
acetic acid and formaldehyde in an aqueous solution.
3. Results
3.1 The Classification System of Giant Trevally
Giant trevally belongs to order Perciformes, family
Carangidae, genus Caranx, species Caranx ignobilis
(Forsskal, 1775). The English name is giant trevally
and the local name is Vau.
3.2 Some Morphological Characteristics
The measurement criteria of morphological
characteristics as proposed by Lowe-McConnell (1971)
and Grant & Spain (1977), updated by Ref. [2] in
biological research are presented in Table 1.
Giant trevally (Caranx ignobilis) has a big head, big
mouth, mouth under thrown up on, inside contains
sharp teeth, flat body, with a body length (TL) in 3.13
times body height (BH) and in 4.19 times head length
(HL) (i.e., TL/BH = 3.13 and TL/HL = 4.19), head
length in 4.14 times the diameter of the eye (ED) (i.e.,
HL/ED = 4.14). Big round eyes have fat layer
covering the outside, with four nostrils and each side
has two holes. Giant trevally fish often change color
according to the environment; when there is the same
size 10 cm and on the body with the black stripes, the
adults have gray body white or yellow depending on
species and the environment where they live, and the
abdomen is white. There are two dorsal fins; the 2nd
dorsal fin is gray and the outer edge is black, upper
lobe of caudal fin is black outer edge, the lower lobe
of the outer edge is pale yellow, and pelvic fins is
trimmed white. The body covering is round and oval
scale. The pectoral fins, dorsal and anal fins are
yellow to fish and also called Giant trevally contract
yellow fin.
3.2.1 Description of Morphology
Dorsal (D1 = VII; D2 = I, 20): include two dorsal
with dorsal 1 has seven spines; dorsal 2 has one spine
and 21 soft rays has to branch.
Pectoral fin (P = 19) has 19 branched soft rays,
crescent-shaped, longer than the first length.
Ventrals (V = I, 4) has one spine and four soft rays.
Anus (A1 = I-III, A2 = 17-19) have two spines anal
forward split followed by a sequence with soft rays
branching spines include 17-19 soft rays.
Tail fin (C = (19 – 23) + 2). Tail lobe is divided into
two clear, and each fin consists of 19-23 branched
rays with soft spikes. A top of side edge lobes has
yellow black colour, and the lower margin lobes has
pale yellow colour.
The line has a distinct texture and moderately long,
curved part intersecting with the straight part below the
second dorsal fin lobe. Part of the road curved sides has
58-64 scales. Connections part includes one row
connected continue, consisting of 31 layers (Fig. 2).
3.2.2 Biometric Indicators
The indicators of body (HL, ED, high body BH) in
a correlation with TL are considered as an indicator of
biometric (bio-metric index). In each index link
between the target TL (HL/ED; TL/BH), the average
value of the index will be determined biometric
following Fig. 3, according to Bayagbona (1963)
updated Ref. [3]. If in all size groups of fish research,
biometric indicators of each individual characteristics
Fig. 1 Caranx ignobilis Forsskal, 1775.
Biological Features and Distribution of Giant Trevally (Caranx ignobilis Forsskal, 1775)
in Tam Giang-Cau Hai Lagoon Systems, Vietnam
551
Table 1 Morphological characteristics of giant trevally (n = 50).
No. Morphological variables Units Mean Min-Max SD
1 Body weight (W) g 1,993.954 2.2-4,500 1,223.98
2 Body length (TL) cm 45.66196 5.15-70.0 17.56
3 Head length (HL) cm 10.543 1.45-19.0 4.23
4 Front spines (PD) cm 13.627 1.65-24.6 6.60
5 Eye length cm 3.568 0.35-7.4 2.03
6 Space between two eyes cm 4.512 0.5-8.1 2.08
7 Eye dimension (ED) cm 2.611 0.4-4.9 1.18
8 Above mouth length cm 5.0418 0.6-9.0 2.30
9 Below mouth length cm 4.358 0.5-7.8 2.08
10 Anus length cm 15.02 1.1-24.4 6.72
11 Body height (BH) cm 14.05 1.9-22.3 5.55
12 Head height cm 12.592 1.7-21.1 5.15
13 Mouth width cm 3.493 0.4-6.2 1.51
14 Front dorsal spine width 1 cm 3.983 0.7-6.3 1.35
Behind dorsal spine width 2 cm 7.425 0.6-13.4 3.32
15 Front dorsal spine width 1 cm 6.603 0.7-18.6 3.06
Behind dorsal spine width 2 cm 13.644 1.5-20.9 5.21
16 Breast spine length cm 12.098 1.1-20 5.21
17 Breast spine width cm 2.476 0.3-5.25 1.21
18 Anus spine width cm 7.182 0.7-12.3 3.12
19 Anus spine length cm 12.662 1.4-24 4.83
20 Belly spine length cm 5.444 0.6-9.6 2.38
21 Belly spine width cm 1.5928 0.1-3.2 0.79
22 Mouth high cm 8.308 0.9-15.2 3.72
23 Body high at dorsal cm 13.657 1.9-21.9 5.50
24 Body high at chest cm 12.841 1.8-20.4 5.00
25 Body high at anus cm 13.529 2.0-20.8 5.15
26 Tail spine high cm 13.186 1.2-21.2 5.59
27 Tail length cm 6.807 0.5-13 3.30
indicate each odds decreased continuously, then
characteristics survey shows a positive correlation (+).
On the contrary, the characteristics of the survey was
inversely correlated (-). If the index does not change
biometric, means the development of the survey
indicators in relation to the correlation length and a peer
[7]. Thus, based on Fig. 3, it is found that the correlation
between TL/BH, TL/HL and HL/ED compared to TL is
a positive correlation.
3.3 Growth Characteristics
3.3.1 Age Structure of Fish
Table 2 and Fig. 4 showed the age distribution of the
fish caught from sea and lagoon in four groups: <
1-year-old group (0 +), > 1-year-old group (1 +), >
2-year-old group (2 +), > 3-years-old group (3 +). The
length of individuals under age group 0 + ranged from
51.5 mm to 395 mm with average 234.733 mm, and the
weight ranged from 2.2 g to 1,230 g with average
429.11 g, respectively. The length of individuals aged 1
+ ranged from 382 mm to 444 mm with average
419.730 mm, the corresponding volume ranged from
1,300 g to 2,200 g with an average of 1,608.5 g,
respectively. The length of individuals aged 2 + ranged
from 530 mm to 573 mm with average 557.257 mm,
and the corresponding volume ranged from 2,300 g to
3,140 g in average 2,760.7 g, respectively. The length
of individuals aged 3 + ranged from 563.3 mm to 673
mm with average 646.1 mm, and the corresponding
amount ranged in 3,200-4,500 g, averaging 3,750 g.
Biological Features and Distribution of Giant Trevally (Caranx ignobilis Forsskal, 1775)
in Tam Giang-Cau Hai Lagoon Systems, Vietnam
552
Fig. 2 Fish scales.
Fig. 3 The index of personal biometric giant trevally body length of each age group.
Table 2 Age and distribution composition.
Age Length L (mm) Weigh W (g) Numbers
Mean Min-Max SD Mean Min-Max SD Frequency %
0 + 234.733 51.5-395 139.711 429.11 2.2-1,230 466.61 15 30
1 + 419.730 382.0-444 15.000 1,608.5 1,300.0-2,200 258.03 13 26
2 + 557.257 530.0-573 16.734 2,760.7 2,300.0-3,140 240.55 14 28
3 + 646.100 563.3-673 36.661 3,750.0 3,200.0-4,500 396.41 8 16
Mean 438.958 51.5-673 172.533 1,919.93 2.2-4,500 1,253.47 50 100
3.3.2 Correlation between Length and Body Weight
of the Fish
In the process of growth and development of fish,
the increase between length and weight has a
relationship with each other. After analyzing 50
samples of fish with many sizes and different age
groups, the correlation between the length and weight
of fish is shown in Fig. 5.
Based on the formula Beverton-Holt (1956)
updated by Ref. [3] and analyzing the research results,
it was obtained that the correlation between length (L)
and weight (W) of giant trevally is expressed as Eq.
(4)
W = 0.025L2.8898 (4)
From Fig. 5, the growth in length and weight of
giant trevally close relationship with each other is
clearly reflected in the correlation coefficient R2 =
0.987, and this is positively correlated, meaning that
when length increases, the volume of fish Vau also
increased. However, the growth and length of giant
TL/BH
Biometric index
Biological Features and Distribution of Giant Trevally (Caranx ignobilis Forsskal, 1775)
in Tam Giang-Cau Hai Lagoon Systems, Vietnam
553
Fig. 4 Age structure of fish.
Fig. 5 Correlation between length and body weight of
the fish.
Fig. 6 Teeth and stomach of giant trevally.
trevally was uneven shown in Fig. 5. Particularly, in
the early stages (age 0 +), the length increased, the
volume increases slowly. By the stage 1 +, 2 +, 3 +,
giant trevally showed rapid growth in volumes and
slow growth in length. Maybe at this stage, fish have
increased in volume in relation with nutrient
accumulation process, and the increase in size in early
life is due to adaption in competition for food and
animal data to ensure survival.
3.4 Nutritional Features
3.4.1 Anatomy of the Digestive Organs of Giant
Trevally
The results observed showed that a giant trevally
species have big heads, wide mouth, mouth under
upwards, mouth width of 50 samples ranging in
0.4-6.2 cm and average of 3.493 + 1.51 cm; the upper
jaw contained a series of sharp fangs outside with
uneven distribution and the smaller teeth in innermost,
while mandibular teeth have a conical line, and inside
there are many teeth almost distributions as shown in
Fig. 6. Gill rakers are long and thin situated on bone
sparse supply carries towards oropharyngeal cavity.
On the supply carries, there are 18-24 carries combs,
each side has the four leaf bearing and multi-motor
bearing is surrounded by the gill cover. Esophagus is
short, thick-walled, and many folds present in the
esophagus should be so elastic lug that fish can
swallow large prey. J-shaped stomach is large and
thick wall capable of contraction. The fish has a short
bowel, therefore it can be recognized that this fish can
eat origin animal feed. They are carnivorous fish and
in most of the habitat, they are known as independent
predators. The research results are consistent with
previous studies of some scientists, who believed that
food of giant trevally was the primary prey of
Biological Features and Distribution of Giant Trevally (Caranx ignobilis Forsskal, 1775)
in Tam Giang-Cau Hai Lagoon Systems, Vietnam
554
crustaceans, molluscs and mollusks. The strategic
large predatory fish like to ambush their prey. The diet
is similar, mainly including fish eels, small squid,
octopus, mantis shrimp, lobster and other crustaceans.
3.4.2 Correlations between Gut Length (Li) to Body
Length (Lo)
According to Nikolsky (1963) updated by Ref. [3],
the species of fish which are fond of animal feed
would be valuable of Li/Lo ≤ 1, omnivorous fish have
Li/Lo = 1-3 and fish with natural feeding about plants
have Li/Lo ≥ 3. From collated results in Table 3, it
was shown the coefficient RLG = 0.468 and it can be
concluded that giant trevally feeding inclined to
animal due to Li/Lo = 0.468 ≤ 1.
3.4.3 Feeding Analysis by Occurrence Frequency
To determine the composition of giant trevally
feeding, the food in the gastrointestinal tract with 50
fish samples were analyzed and divided according to
the size based on the length of the largest and smallest
fish by means of determining occurrence frequency of
these foods in the digestive tract. The results about
occurrence frequency of foods in the digestive tube
lugs fish are presented in Table 4. It can be seen that
the food of giant trevally feeding is mainly animal.
3.4.4 Natural Food of Fingerlings
Analyze food in the digestive tract of 15 specimens
of giant trevally following different size group, where
the smallest was 2.0 cm and the largest was 12.0 cm,
to determine the natural spectrum of giant trevally
fingerlings feed. The analysis results of giant trevally
fingerlings are very diversified, including three groups
of phytoplankton and animals (zooplankton and small
size) and organic humus (decomposed food).
According to Table 5, concrete phytoplankton group
includes 14 species of four phylums. Among them,
Chlorophyta phylum had the highest rate with six
species and made up 42.8% of phytoplankton group;
Bacillariophyta phylum with five species made up
35.7%; Cyanophyta phylum had two species and
made up 14.2%; the least was Euglenophyta phylum
with one species and made up 7.3%. The spices of
animals consist of zooplankton and small size animal;
it had 19 species on seven classes. Among them, the
Copepoda class had the highest rate with eight species
and 42.1% of animal group, and the lowest rate was
Gastropoda class with one species and 5.26% of
animal group. In Osteichthyes class, it just can be
identified in order and unidentified in species. In
addition, the organic humus component wad also
identified. It consists of algae and decomposing
animal, accounting for 30% high present in the
digestive tract.
3.4.5 Fat Level of Giant Trevally
According to Nikolsky (1963) updated by Ref. [3],
the method of Fulton (1902) and Clark (1928) [3]
was used to determine the difference of fat ratio, the
level of individual nutrients accumulate of giant
trevally.
According to the results of the study (Table 6), fat
levels of individuals of giant trevally varied between
age groups. The fat level III and IV appeared mostly
in all age group. At the age group 2 + and 3 +, the fat
Table 3 The variation rate Li/Lo by size (n = 50).
Measurement indicators Mean Min Max
Total length (mm) 438.958 ± 172.5 51.5 673.0
Gut length (mm) 205.780 ± 66.3 65.0 273.0
Correlations between gut length and total length (RLG) 0.468 0.03 1.00
Table 4 The results of feeding analysis by frequency of occurrence (n = 50).
Dietary composition The number of caught times Frequency of occurrence (%)
Crustacean 40 80
Fish 32 64
Ink 24 48
Mollusca 10 20
Biological Features and Distribution of Giant Trevally (Caranx ignobilis Forsskal, 1775)
in Tam Giang-Cau Hai Lagoon Systems, Vietnam
555
Table 5 The result in the digestive tract of giant trevally fingerlings (n = 15).
Category Name of food Size group (cm)
2-7 7.1-12.0
(1) Phytoplankton
I Bacillariophyta
1 Cerataulina pelagica - +
2 Thalassiosira sutilis + -
3 Coscinodiscus sp. + +
4 Navicula sp. + -
5 Achnanthes sp. + -
II Chlorophyta
6 Pediastrum sp. + +
7 Selenastrum sp. + -
8 Microsporaceae + +
9 Oophila amblystomatis + -
10 Chlorella sp. - +
11 Chlorococcaceae + -
2-7 7.1-12.9
III Euglenophyta
12 Phacus sp. + +
IV Cyanophyta
13 Microcystis sp. - +
14 Chroococcus - +
(2) Animal
V
Crustacean class
15 Scylla paramamosain (Estampador, 1949) - +
16 Penaeus monodon Fabricius, 1798 - +
VI
Rotatoria
Asplanchnidae order
17
Asplanchna priodonta
Gosse, 1850
+ +
VII
Cladocera
(a)
Sididae order
18
Diaphanosoma sari
Richard, 1894
- +
(b)
Bosminidae order
19
Bosminopsis deitersi
Richard, 1895
+ +
VIII
Copepoda
(a)
Pseudodiaptomidae order
20
Schmackeria dubia
Poppe & Richard, 1979
+ +
21
Pseudodiaptomus incisus
Shen & Lee, 1963
- +
(b)
Acartidae order
22
Acartia clausi
Giesbrecht, 1889
+ +
23
Acartiella sinensis
Shen & Lee, 1963
+ +
(c)
Oithonidae order
24
Limnoithona sinensis
(Bruckhardt, 1912)
- +
25
Oithona nana
(Giesbrecht, 1892)
+ -
(d)
Temoridae order
26
Temora turbinate
(Dana, 1849)
+ +
27
T. discaudata
Giesbrecht, 1889
+ +
Biological Features and Distribution of Giant Trevally (Caranx ignobilis Forsskal, 1775)
in Tam Giang-Cau Hai Lagoon Systems, Vietnam
556
(Table 5 continued)
Category Name of food Size group (cm)
2-7 7.1-12.0
IX
Polychaeta class
(a) Chrysopetalidae
order
- +
(b) Hesionidae
order
+ +
(c) Nephthydidae
order
+ +
(d) Opheliidae
order
+ +
XI Osteichthyes class
28 Stolephorus
sp.
+ +
29
Lish larval
+ +
30
Fish eggs
+ +
X Bivlavia class
(a) Corbiculidae order
31 Corbicula sp. - +
(b) Arcidae order
32 Anadara sp. + +
(c) Placunidae order
33 Placuna sp. + +
XI Gastropoda class
(a) Potamididae order
34 Cerithidea sinensis (Gmelin) + +
(3) Organic humus
Disintegrate animals + plants + +
Table 6 The accumulation of fat degree by giant trevally age group.
Age group
Fat levels Total
0 I II III
IV
n % n % n % n % n % n %
0 + 3 6 2 4 4 8 4 8 2 4 15 30
1 + 0 0 0 0 5 10 4 8 6 12 15 30
2 + 0 0 0 0 0 0 5 10 7 14 12 24
3 + 0 0 0 0 0 0 1 2 7 14 8 16
Total 3 6 2 4 9 18 14 28 22 44 50 100
Table 7 The fat ration of giant trevally.
Age group Fulton ratio (1902) Clark ratio (1928) N
n %
0 + 3,317.7 10-6 2,843.23 10-6 15 30
1 + 2,175.2 10-6 2,027.66 10-6 13 26
2 + 1,595.3 10-6 1,526.18 10-6 14 28
3 + 1,390.4 10-6 1,341.16 10-6 8 16
was the most 14% in level IV, and at this age there
was not fat in stage 0, I, and II. In the age group 0 +,
the fat was caught at all stages from 0-IV, and in
group 1 +, the fat was not caught in stages 0 and I.
Thus, it can be concluded that the fat levels of fish
species with giant trevally is very high. Thus, it can be
concluded that the fat levels of fish species with giant
trevally is very high. Table 7 showed that there are
relationships between ages and fat accumulation by
Fulton ratio (1902) and Clark ratio (1928) with
percentages of fish grow-up 3 +, they can have mature
soon gonads in culture stages in cages.
Biological Features and Distribution of Giant Trevally (Caranx ignobilis Forsskal, 1775)
in Tam Giang-Cau Hai Lagoon Systems, Vietnam
557
3.5 Reproductive Characteristics
Only a small number of fish species differ in
outside appearance between males and fingerlings
(stingrays, sharks), and some species have differences
in spawning time (salmon males have a longer snout
in female children during reproduction). Many fish
species have distinctive characteristics of sex and can
be identified through the external morphological
characteristics, such as the level of micro-smooth
chest in carp, big belly and protruding genital growth.
However, for some wild fish species, identification of
sex based on outside shape is difficult, especially for
not sexually mature fish.
For individuals of giant trevally, some giant trevally
fish have eggs with size > 3.5 kg/head. At the same
time, a survey on fishing capture on lagoon and sea
was done, but not found yet any fishes having eggs.
Besides, the gonads of giant trevally fish were only
identified in phase I, II, III of aquaculture farming
with cages and was observed clearly in Fig. 7 on
phase III.
Phase I: For individuals with gonads in stage I, it
can not distinguish between male and female gonad
when observed with the naked eye (Figs. 7 and 8).
The back of gonads has a lot of fat clinging to, if not
carefully observe it very easy to mistake for a part of
gonads, as it is the same color as the gonads and also
vascular distribution. Gonads have the distribution of
blood vessels, but small numbers, very small diameter
and no ramifications. Gonads have very small volume
and cell attributes were observed at ovarian in phase I;
under the microscope, the acolytes appeared in
synthetic period and also gonad cells developed, so
the next, the ratio between the gonad diameter and the
body diameter of the fish species was compared with
other fish species. Results showed that the ratio of
gonad in Giant trevally was slowly and smaller.
Phase II: TSD has become larger, but still not goes
to mature as expecting, when observed with the naked
eye, except in cases of ovarian at late phase II by this
time, some small eggs had formed as beads. Yellow is
the first period of growth in nutrition which can be
seen by naked eye. Blood vessels are distributed in
more gonads, and small blood vessels branch run
around gonad to make gonad white roses. Due to the
increase of protoplasm, egg cells become larger and
uneven due to the tension of the plasma membrane to
the cell polygon-shaped eggs. The relationship
between egg diameter and sex cell diameter was
deflected to a corner.
Besides, there are interstitial spaces for many gonad
cells still in synthetic period. The size and weight of
the ovaries increased significantly, so that the naked
eye can distinguish the males and females. Ovaries
occupy two-thirds of the volume of the abdominal
cavity. Ovaries have a lot of blood vessel distribution,
along the ovaries are the major blood vessel diameter
and they are divided into smaller blood vessels
surrounding the ovary. Use the hand to stroke along
belly, there is egg to flow out (Fig. 9).
Phase III: In ovary of giant trevally, a big difference
of size and different development phases of the
oocytes can be seen in the nutritional growth period.
Fig. 7 The gonad of giant trevally.
Fig. 8 Ovarian of fish at phase I.
Biological Features and Distribution of Giant Trevally (Caranx ignobilis Forsskal, 1775)
in Tam Giang-Cau Hai Lagoon Systems, Vietnam
558
Fig. 9 Ovarian of fish at phase II.
Fig. 10 Ovarian of fish at phase III.
There are larger cells inaccumulated yolk phase, they
were smaller than the unsaturated cells that is storage
stage the nutrition of oocytes for the next round of
mature. However, the egg cells of small size are also
different with each another (Fig. 10).
4. Discussion
Giant trevally fish is widely distributed in tropical
seas and subtropics of the Indian Ocean and the
Pacific, ranging along the coast of three continents
and hundreds of small islands and archipelagos. In the
Indian Ocean, the easternmost range of the species is
the coast of the African continent, which is distributed
from the Southern to South Africa, North along the
East coast of Africa to the Red Sea and Persian Gulf.
Its scope extends to the East along the coast of Asia,
including Pakistan, India and Southeast Asia,
Indonesian Archipelago and Northern Australia.
Elsewhere in the Indian Ocean, the species has been
recorded from hundreds of small island groups,
including the Maldives, Seychelles, Madagascar and
the Cocos (Keeling) Islands. Sometimes, immature
fish live in the estuaries, upstream river and coastal
lakes in some places, including South Africa,
Solomon Islands, Philippines, India, Taiwan, Thailand,
North of Australia and Hawaii. Through surveys of
households who exploited and lived around Tu Hien
(Vinh Hien) and Thuan An estuaries (Thuan An town),
it is found that hatch of fish (Giant trevally) is in sea,
and larvae growing to fingerlings is under the water
going into the lagoon through two estuaries (Thuan
An and Tu Hien). Most fingerlings are primarily
concentrated in October to April every year, and every
year just has one or two batches in raining seasons,
often slipping into pre-season floods and storms.
Every night, one bottom corral can catch hundreds of
fingerlings, and sizes of fingerlings are around 3-10
cm of length according to Refs. [1, 7, 8].
Biological Features and Distribution of Giant Trevally (Caranx ignobilis Forsskal, 1775)
in Tam Giang-Cau Hai Lagoon Systems, Vietnam
559
Based on the morphological analysis of the body,
results showed that there are some differences among
the lower part on the lateral dorsal, lateral area of the
body, the part near the tail fin fish scales, but
generally fish scales are relatively large with oval, and
bears some general characteristics of bone fish species.
Giant trevally has thin scale, and is oval, central
development, so the growth is flourishing in both the
front and the back of the scales. In different areas of
the body, fish scales, shapes and different sizes were
observed in the study. The larger scales are in the
lateral head of the body, and the front flounce of
larger size is at rear area. Head part of fish has an
abdomen paler, and contains less pigment than the
body part, however, the larger head is not clear; the
growth rings close to the lateral middle have the
largest distance, the color equivalent between belly
parts of fish body is not explicit compared with the
lateral body. Therefore, the length of scabs in the body
on either side of the road was used to determine the
age of fish. According to the results of some previous
studies, the habitat of giant trevally has extensive
salinity, from brackish to marine water environment,
estuaries, bays and lagoons, while the immature live
in the deeper reefs and offshore atolls. In the same
period, the authors lived in a very low salinity waters,
such as coastal regions and rivers upstream, and
tended to prefer turbid waters, as research done by
Smith and Parrish updated by Ref. [9].
Fingerlings were fed crustaceans and small fishes
every day in the culture cages. For individuals
collected and caught from lagoon and sea, it was
showed their diets in Table 4 with 80% of the stomach
of fish and mostly they are small species combined, as
shown in Refs. [5, 10-12]. Fig. 5 showed the growing
rate of body weight and length with significant (P <
0.05) correlation, and the body weight will be
expected to 4-5 kg after three years feeding in lagoon
conditions with dietary composition as in Table 4. Many
fish species have distinctive sex characteristics and
can be identified through the external morphological
characteristics. However, wild fish species are
difficult to identify based on outside sex shape,
especially for not sexually mature fish. For individuals
of giant trevally collected from wild condition, they
have eggs size weighing over than 3.5 kg/head.
Meanwhile, individuals raised in culture condition
showed mature sooner, inducing gonad stage, vascular
distribution. At phase II, gonad becomes larger, but
still not goes to mature as expecting, when observed
with the naked eye, except in cases of ovarian at late
phase II; and mature can reach at phase III with ovary
of giant trevally for oocyte in the nutritional growth
period. The larger ovarian cells are accumulated more
yolk and stored the nutrition of oocytes for the next
round of mature [9].
5. Conclusions
The giant trevally (Caranx ignobilis) is large fish,
big mouth, mouth under thrown up on and inside
mouth contains sharp teeth, flat body, with a total
body length in 3.13 times of body height and in 4.19
times of head length (TL/BH = 3.13, TL/HL = 4.19)
and head length in 4.14 times of eye diameter (HL/ED
= 4.14), pectoral fin rays, dorsal and anal yellow, gray
dorsal, and ventral surface is silver white.
The research results showed correlation between
length and weight of fish Vau is: W = 0.0252 L2.898
and R2 = 0.987, and this is correlated with age
structure of giant trevally groups (0 +, 1 +, 2 +, 3 +).
Composition of food in the digestive tube lugs fish
includes three groups: phytoplankton, animals
(zooplankton and small size animals) and specific
organic humus containing 14 species of phytoplankton
and 19 species of animals. The average correlation
coefficient between gut length and body length of
giant trevally (RLG) is 0.468 < 1, and it can be
concluded that the feeding of giant trevally was
inclined to animal.
Of the 50 samples studied, it could not distuinguish
yet between sexes clearly, may be due to that the time
of sampling does not coincide with the breeding
Biological Features and Distribution of Giant Trevally (Caranx ignobilis Forsskal, 1775)
in Tam Giang-Cau Hai Lagoon Systems, Vietnam
560
season of giant trevally in Tam Giang-Cau Hai lagoon
system. However, only mature female fish for eggs
and male fish for spermatorrhoea were detected.
Results showed that in slice of fish samples, some
gonads were identified in phase I, II, III and the sex
cells and gonads were continuing to grow.
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