Natural spawning and intensive culture of pejerrey Odontesthes bonariensis juveniles
L.A. Miranda1, G.E. Berasain2, C.A.M. Velasco2, Y. Shirojo1,2 and G.M. Somoza1
1 Laboratorio de Ictiofisiología y Acuicultura. Instituto de Investigaciones Biotecnológicas-Instituto Tecnológico de
Chascomús (IIB-INTECH), Chascomús (B7130IWA), Provincia de Buenos Aires.
2 Estación Hidrobiológica de Chascomús, Subsecretaría de Actividades Pesqueras, Ministerio de Asuntos Agrarios, Provincia
de Buenos Aires.
Address correspondence to: L.A. Miranda. Laboratorio de Ictiofisiología y Acuicultura. Instituto de Investigaciones Biotecnológicas - Insituto Tecnológico de Chascomús (IIBINTECH), Chascomús (B7130IWA), Provincia de Buenos Aires, ARGENTINA. E-mail: lmiranda@intech.gov.ar
Keywords: Aquaculture; Pejerrey; Reproduction; Seed production
The pejerrey Odontesthes bonariensis is an
atherinid fish native of the inland waters of Buenos Aires
Province (Argentina). This species has also been introduced
in other Argentinean provinces and some countries
due to the economic movement generated by
pejerrey game fish and aquaculture (Bonetto and
Castello, 1985; Grosman, 1995; Mituta, 2001).
Although pejerrey aquaculture is considered of regional
importance, this activity has not been fully developed
in Argentina. The culture of this species, either
in extensive or semi-intensive systems, can be productive
alternatives in the Argentinean Pampas where more
than 2 millions square hectometers of lagoons have been
described (Reartes, 1995; Espinach Ros et al., 1998;
López et al., 2001). However, some reports have demonstrated
the existence of problems in the feasibility of
pejerrey farming: low growth rates, high mortality in
the first stages and early sexual maturation before fish
reach market size (Luchini et al., 1984; Grosman, 1995;
Grosman and González Castelain, 1996; Gómez, 1998;
Berasain et al., 2000; Colautti and Remes Lenicov, 2001;
Miranda and Somoza, 2001). Then, it is necessary to
perform basic and applied studies in order to establish
pejerrey culture (Strüssmann, 1989; von Bernard et al.,
2002).
A main objective is to control reproduction in order
to obtain a massive production of embryos and larvae
and, if possible, almost all year round. Up to date,
pejerrey seed production in Argentina is being performed
only through the capture of wild fish by gill
nets and by artificial fertilization, according to traditional
methodologies (Ringuelet, 1943), which cause the
dead of all parent fish by manipulations.
In the present work we summarize the results of
our efforts to control pejerrey reproduction in captivity,
for the development of efficient, economically viable
and not pollutant techniques for the production of juveniles
in an intensive system.
Pejerrey broodstocks in captivity
Pejerrey embryos were obtained from the Kanagawa Experimental Station (Kanagawa, Japan) and transported to IIB-INTECH (Chascomús, Argentina) on November, 2001. These embryos are the progeny of an original stock of pejerrey from Chascomús Lagoon sent to Japan in 1965 and kept in captivity for approximately 37 generations. These fish were found to be easier to rear in captivity than those fish obtained from wild parents. The embryos were obtained from natural spawnings, incubated until the stage of "eyes with no pigment", kept in a special thermo box at 17 ± 1°C and transported to Argentina. After 45 h these embryos were immediately transfer to jars to finish the incubation process at the IIB-INTECH aquatic facilities. They were maintained in a close water flow system with a salinity of 0.4%, temperature oscillating between 20 and 23°C and natural photoperiod. The hatched larvae (around 75%) were immediately transferred to indoor 300 l tanks using an open water flow system, salinity of 0.4% and fed ad libitum with artemia nauplii and artificial food specially designed for pejerrey at the Tokyo University of Marine Science and Technology. After one month the larvae were transferred to indoor 3,000 l tanks and maintained at the same conditions.
Natural spawnings in captivity
On July 2003 two groups of fish were transferred
to outdoors 20,000 l tanks with and open water flow
system and a salinity of 0.7%. At the beginning of October,
all fish were separated by sex, measured (standard
length: 25.99 ± 2.14 cm; weight 226.29 ± 63.77g)
and distributed in a proportion of 1.5 male per female
in 2 tanks with 300 fish each. The gonadal condition of
females was evaluated using a catheter following established
techniques (Strüssmann, 1989) and in the case of
males running milt was verified by stripping.
The first group of eggs was observed on October
3rd (22 months after hatching [MAH]), and in a regular
form since October 17th up to December 14th. The eggs
were collected daily every morning using a collecting
bag at the end of a drain tube with no natural or artificial
substrates that may stress parent fish. Water temperature
oscillated between 16.2 and 18.1°C, and
599,000 eggs were collected with 52% of fertilization
rate.
The second spawning season began on August 17th 2004 (33 MAH). At the end of September all the fish
were separated by sex, measured (standard length 30.57± 2.2 cm; weight 400 ± 86.6 g) and distributed in a proportion
of 1.2 males per female using 2 tanks with 290
fish each. The animals were kept in the same conditions,
except that water salinity naturally increased up
to 1.5%. In this case the day length was artificially increased
up to 15 h (between 6 to 21 hs) because it was
already reported that under a long photoperiod regimen
the fish presented spawnings distributed uniformely
during the reproductive season independently of water
temperature (Strüssmann, 1989). In this case, the water
temperature oscillated between 17.5 and 18.3°C.
The fish spawned regularly until December 29th,
and during that time 2,136,952 eggs with a fertilization
rate of 35% were collected. The lower fertilization rate
observed in this second compared to the first reproductive
period could have been caused either by the lower
male:female ratio or by the higher water salinity in the
second period. First, it is important to note that pejerrey
sperm volume obtained by stripping either in natural
conditions or in captivity is scarce (Strüssmann, 1989;
Miranda et al., 2001), then it is possible that several
males are nedded to fertilize the eggs produced by a single female as already shown in a related species
Menidia menidia (Conover and Kynard, 1984) and suggested
in pejerrey (Calvo et al., 1977). Another possibility
is that the increase in salinity altered the pejerrey
sperm motility, because it was already demonstrated that
pejerrey spermatozoa are motile in hypoosmotic to
slighty hyperosmotic media in relation to the seminal
fluid (Renard et al., 1994). It is important to consider
that in our study the osmotic pressure of pejerrey seminal
fluid was around 320 mOsm/kg and the osmotic
pressure of the water was around 480 mOsm/kg.
In Buenos Aires Province, pejerrey shows an intense
natural spawning period during the spring, from
the end of August to the beginning of December (Calvo
and Morriconi, 1972). This data are in accordance with
the reproductive season observed in captivity, though
we observed that the breading season can be extended
in captivity.
During the two breeding seasons reported in this
study the mortality rate was almost negligible, showing
that it is possible to control pejerrey reproduction in
captivity. However, it is important to work on the synchronization
of spawning and to get higher fertilization
rates by the manipulation of environmental clues such as photoperiod, salinity and/or through hormonal treatments.
Juveniles production
Groups of pejerrey embryos obtained at the IIBINTECH aquatic facilities were transferred to the "Estación Hidrobiológica de Chascomús" (EHCh) in order to set up the production of juveniles in an intensive system. This activity was performed in two phases: one indoor phase lasting for approximately 36 days and an outdoor phase of 25 days.
Indoor phase
In this phase, 25,000 larvae hatched between November
16 and 22 and 14,000 larvae hatched between
November 22 and 28, were seeded in two 1,800 l tanks
(1 and 2 respectively). During the first 10 days a close
water flow system was used with a salinity adjusted to
1%. Then, the system was changed to an open water
flow system and the salinity was lowered to 0.3%.
Larvae were fed with nauplii of Artemia sp., pelleted
artificial food and zooplankton (rotifers Bracchionus
spp., filtered from a previously fertilized pond) following the schedule shown in Table I. During this period
the total amount of Artemia eggs offered was 4,850 g
(hatching rate around 90%) from 5 g to 250 g. Rotifers
were 9,753,194 individuals for tank 1, and 4,378,848
individuals for tank 2. From this total amount of nauplii and rotifers, 64% was offered to tank 1 and 36% to
tank 2 due to the differences in pejerrey number in each
tank. Since day three, 250 mm pelleted food (Kyowa,
Co, Japan) was also supplied; 969 g to tank 1 and 635 g
to tank 2. During this phase water temperature oscillated
between 18.5 and 20.8°C.
Table I. Feeding schedule during the indoor phase
After 39 days after hatching (DAH) in tank1 and 36 DAH (tank 2) all juveniles were counted and measured (Table III). During this phase the survival rate was 84.5% in tank 1 and 82.8% in tank 2 (Table IV).
Outdoor phase
After the indoor phase, 32,400 juveniles were transferred from tanks 1 and 2 to an outdoor 20,000 l tank with and open water flow system and a salinity of 10 g/ l. Juveniles were fed with nauplii, artificial food (Kyowa, Co, Japan) and zooplankton. The total quantity of nauplii supplied was obtained from 7,535 g of Artemia eggs (mean hatching rate 75%). During the first 13 days 400mm pelleted food (a total of 1,275 g) was offered to the fish and then changed to 700 mm until the end of the period (3,790 g, Table II). In this case, the zooplankton supplied was mainly composed by cladocerans (16,867,387 individuals) and copepods (18,843,220 individuals). The water temperature oscillated between 18.7 and 23.7°C. After 25 days in outdoor conditions (61-64 DAH), juveniles were counted and measured (Table III). The survival rate during this phase was 73% (Table IV) and the overall survival rate during the 61-64 days was obtained 60.76%. However, it is important to note that the mortality rate was increased by the transfer of fish from indoor to outdoor tanks, probably caused by manipulation stress.
TABLE II.
Frequency and feeding schedule during the outdoor phase
TABLE III. Pejerrey measures during indoor and outdoor phases
TABLE IV. Density, survival rate and production during indoor and outdoor phase
The data obtained for standard length in this study (Table III) was similar with those obtained by Berasain et al. (2000) using an intensive system, and higher than those obtained by Colautti and Remes Lenicov (2001) using a cage system, and those obtained by Grosman and González Castelain (1996) using a combination of natural and artificial food (Fig. 1). However, the weight values obtained in this study (Table III) were lower than those obtained by Reartes (1995) and Berasain et al. (2000), both using lower densities.
FIGURE 1. Comparison of standard length (L st)
obtained in different studies
The survival rate obtained in this study (60.7%) is
higher to those reported using different methodologies
and systems (Luchini et al., 1984; Grosman and
Gonzalez Castelain, 1996; Berasain et al., 2000; Colautti
and Remes Lenicov, 2001) and it was lower than the
obtained by Reartes in 1995 (89.2%). However, it should
be pointed that in all cases the initial densities were significantly
lower than the one used in this work (see
Berasain et al., 2000).
Taking together all these data show that it is possible
to get massive productions of pejerrey fingerlings
(Table IV) starting from a high initial density using an
intensive system. However, it is necessary to develop
cheaper ways of production by replacing both the nauplii of Artemia and the artificial food by the use of natural
zooplankton.
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Received on April 1, 2005.
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