ESTIMATING AGE AT RECRUITMENT OF GLASS EELS (Anguilla bicolor pasifica)
FROM MALUNDA WATERS, WEST SULAWESI,
AS REVEALED BY OTOLITH MICROSTRUCTURES
Faisal Amir1) , Achmar Mallawa1), Budimawan1), Joeharnani Tresnati1)
1)
Fakultas Ilmu Kelautan dan Perikanan Unhas Makassar
ABSTRACT
The purpose of this research was to determine the early life history of the tropical eel, glass
eel Anguilla bicolor pasifica in Malunda waters, West Sulawesi. Otolith microstructure of glass eel
of A. bicolor pasifica was examined. The samples were collected from the Malunda Waters, West
Sulawesi, since 2008. Based on nine months sampling (April to December) by triangular scoop nets,
the mean duration of metamorphosis (mean±SD) was 18 to 25 d (21.7±2.0 d) and ages at recruitment
were 111 - 162 days (133.3 ± 15.5 d). The hatching period was estimated occurring almost at the
entire year. Based on the time and the age of recruitment of A. bicolor pacifica at the Malunda
waters, it was suggested that hatching season of the species occurred yearly. Positive linear
relationships were found between age at metamorphosis and age at recruitment. This evident
demonstrated that the early metamorphosis of recruited glass eel were the early age.
Key words: Age at recruitment, glass eel of Anguilla bicolor pasifica, otolith microstructure
INTRODUCTION
Eel is an important commercial fish species and potentially cultivated. In the world, there are
19 species or subspecies of fish discharge is known, 10 species of which inhabit the tropical
region (Tesch, 1977), with 7 species in the western Pacific, namely in the waters around
Indonesia. Eel is catadromous fish, grow on the waters of estuaries or inland fresh waters
until sexually mature adult and then returned to the area pemijahannya oceanic waters to
spawn once during his life before dying. Prediction of migration patterns of eel larvae from
spawning areas to estuarine waters is very difficult to observe in practice. The use of tagging
techniques to determine the route of migratory fish is very difficult to apply in eel larvae are
very small. Thus, by using signs that a lot of internal naturally reflected in the otolith (one of
them) may explain some of the questions about the life history of fish, such as time of birth
and age of the first seed to the estuary waters that will affect the success of the regeneration
of fish stocks in the eel river waters. Otolith has been used to determine age of fish by experts
in many countries due to accretion annuli depicted circle-based daily, so that critical
information about age and growth can be determined in each individual fish.
METHOD
Eel Anguilla bicolor pasifica seeds collected by seser (triangular scoop nets) in the coastal
waters of West Sulawesi Malunda with latitude and longitude position of the LS 02o58'37, 4
"and BT 118o51'25, 8", in April to December 2008. Eel are caught with sero (triangular
scoop nets) preserved in 70% alcohol after sampling. For the purposes of observation and
early-life stadia tropical eel age, number of samples collected and given a raised its otolith
apoxi liquid resin glue and dried for 24 hours at room temperature. Otolith smoothed with
fine sandpaper no. 1500 and 2000 to appear central otolith core. Next otolith polished by
using diamond paste size of 3 micrometers or no. 3000 to otolith core pins. Before the end of
the observation with a microscope serial Olympus BX-50 brands with up to 1000 times
magnification, the otolith aquades subsequently cleaned with a solution of 5% were given
EDTA (Ethylene Diamine Tetra Acetate) for 45 seconds (Budimawan, 1997). The aging of
fish seed discharge is based on a reading of the image magnification 1000 times. Daily circle
who captured image is calculated one by one from start to hatch until age caught from the
results print out. To reduce the bias of the reading age, each image sample daily growth rings
were counted 2 times.
RESULTS AND DISCUSSION
Otolith microstructure.
Otolith oval, transparent, with a black circle in the center (nucleus). Around the core there is
a strong circle daily as a sign that indicates the time when the first hatch and the larvae eat the
circle that is very clearly seen in around the core. Daily circle pattern formed on the tropical
eel species (Fig. 1.) Same shape as that of temperate eel, Anguilla species such as the A.
anguilla (Mallawa, 1987; Poole et al., 2004), A. rostrata (Wang and Tzeng, 1998; Jessop et
al., 2008), A. australis (Arai et al., 1999c), A. marmorata (Budimawan, 1997; Kuroki et al.,
2005), A. bicolor pacifica (Arai et al., 1999b), A. celebesensis, A. marmorata and A. bicolor
bicolor (Arai et al., 1999a), A. dieffenbachi (Marui et al., 2001), and A. rostrata (Wang and
Tzeng, 2000).
ZM
ZL
C
FF
Figure 1. Daily circle pattern formed on the otolith Anguilla bicolor pasifica (TL = 44 mm
with W = 0.08 g, ID = 7, May 3, 2008). Description: C = Cor, ZL = Zone
Leptocephalus, FF = First feeding, ZM = Zone Metamorphosis (scale X10)
Daily circle is formed starting from its core that has accumulated outward from the
core. Circle marks the first time the larvae begin eating fish marked with a fairly clear. The
calculation of the daily cycle starts from the sign toward the outer core of the otolith. Daily
rate of formation of the circle in the early stadia discharge pattern appeared different. This
difference has to do with the individual growth process consisting of various stadia of life and
perhaps also the influence of environmental changes. Change the width of the circle formed
daily reflecting the development of stadia stadia leptochepalus toward glass eel or elver in the
process in the natural habitat of many changes. Beginning with the stadia leptocephalus living
flowing and drifting. In this phase of larval fish can not swim actively for the body structure
of a rudimentary form.
Age
Age and duration of Metamorphosis
The average age in the early phases of metamorphosis of Anguilla bicolor pasifica ranged
from 89 to 139 days (111.6 ± 15.46 days) with an average duration of the phase of
metamorphosis ranged from 18 to 25 days (21.7 ± 2.0 days). Age and duration of phases of
metamorphosis remained throughout the year. Leptocephalus will take approximately 3 to 5
months to reach a phase of metamorphosis after birth. Individuals with a time of birth earlier
and faster growth rate started earlier metamorphosis, therefore, age at metamorphosis may
change as the result of differences in spawning time.
Umur Rekrutment (hari)
Age at recruitment
The average age at recruitment Anguilla bicolor pasifica ranged from 111 to 162 days (133.3
± 15.5 days). Linear relationship between age at metamorphosis and recruitment age shown
in Figure 2. The same observation temperate fish eel Anguilla japonica (Tsukamoto and
Umezawa, 1994), A. australis (Arai et al., 1999c), A. Anguilla and A. rostrata (Arai et al.,
2000) and A. dieffenbachi (Marui et al., 2001). Age recruitment remains throughout the year.
Age differences in recruitment among species related to differences in age at the beginning of
metamorphosis of each species.
200
Anguilla bicolor pasifica
y = 0.997x + 21.93
R² = 0.988
N = 15
150
100
50
0
0
20
40
60
80
100
120
140
160
Umur Metamorphosis (hari)
Figure 2. Metamorphosis and the age old relationship of glass eel recruitment is caught in the waters
Malunda, 2008
By incorporating the flow velocity (V) maximum Makassar Strait, Sulawesi Sea,
Mindanao currents, and North Equatorial currents, respectively 0.12; 0.25; 0.75, and 0.5 m /
dt in the equation S = V xt, and the current direction (Wyrtki, 1961) affecting ruaya the
location of anadromous larval eel spawning area A. bicolor pasifica Malunda that recruitment
into the waters is at an average distance of 3166 km or 1709 nautical miles.
Eels are semelparous, reproducing only once on the high seas before dying. Eel fish
eggs are planktonis and will hatch after 2 days (Satoh et al., 1992; Aoyama, 2009). Newborn
larvae (preleptocephalus), live from the egg yolks until supplies were 8 days prior to the use
of food from outside sources (Tanaka et al., 2001). When the eel larvae have been taking
food from the outside and grow, the larvae are drifting toward the shoreline south of the
eastern part of Filipinos, is deflected by the flow of Mindanao to the south towards the
Sulawesi Sea (Arai et al., 2001 and Kuroki et al. , 2006 in Aoyama, 2009), which is then
entered into the Makassar Strait. In phase leptocephalus eel fish will enter the waters of
continental shelf, the larvae underwent metamorphosis with a duration
average of 21 days. Larvae that enter the phase of metamorphosis is not eating (Tesch, 1977),
later changed to the glass eel phase (transparent) to get caught in estuary waters Malunda
Majene District of West Sulawesi.
From the analysis of fish eel recruitment age of 133.3 ± 15.5 days showed that the
seeds of eel Anguilla bicolor pasifica that will do ruaya anadromous to freshwater is
generally a young age. It is associated with the perfection of the formation of organs of eel
fish, which in turn will greatly affect an individual's ability to pass fish eel strong factor in the
estuary of the river water flow in the circuit anadromousnya migration for individual growth
into the river upstream. The success of fish seed discharge is passed through the transition
from saltwater to freshwater will affect the strength of the success in the regeneration of the
discharge of existing fish populations.
Birth Time
Time of the alleged birth of the calculations behind (back calculated) of the sampling time
and age were found, indicating that larval fish eel recruitment to estuaries Malunda waters
distributed throughout the year from December 2007 until June 2008. Glass eel spawning
season of this species have been found throughout the year in the waters of estuaries
Malunda, with the initial parameters such as duration of life cycle phases and age of
recruitment leptocephalus be fixed throughout the year. Thus, the spawning season A. bicolor
pacifica can occur throughout the year.
CONCLUSION
Age of eel Anguilla bicolor pasifica that recruitment into the estuary waters of West Sulawesi
Malunda range 111 to 162 days (133.3 ± 15.5 days) with the distance from the spawning
ground it migrates around 3166 km or 1709 miles. Spawning season occurs throughout the
year with remain age of recruitment.
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