Effect of photoperiod and feeding schedule on growth
and survival of larvae of the fighting conch Strombus pugilis Linné,
1758 (Mollusca, Gastropoda)
- División Académica de
Ciencias Agropecuarias (DACA) de la Universidad Juárez Autónoma de Tabasco
(UJAT), Km 25 carretera Villahermosa-Teapa R/A La Huasteca 2ª. Sección,
Villahermosa, Tabasco, C.P. 86260, Mexico
- CINVESTAV IPN Unidad Mérida,
Km 6 antigua carretera a Progreso, Mérida, Yucatán, C.P. 97310, Mexico
ABSTRAK
Pengaruh penggabungan antara jadwal pemberian makan
dan penyinaran dengan cahaya pada keong, Strombus
pugilis (Linné, 1758). Pertumbuhan larva dan kelangsungan hidup
diaplikasikan dengan menggunakan dua jadwal pemberian makan (12 jam dan 24 jam
pemberian pakan) dan dengan tiga fotoperiod (tanpa penerangan, 12 jam penerangan
cahaya dan 24 jam penerangan cahaya). Uji makan dan fotoperioda dilakukan dalam
tiga bulan (Mei, Juni dan Juli). Pengukuran panjang cangkang dilakukan setiap
dua hari untuk melihat hasil dari pertumbuhan untuk setiap perlakuan. Tiga
percobaan, kondisi tanpa cahaya terus-menerus dan pemberian pakan pada larva
terlihat efek pertumbuhan yang lebih tinggi (42 μm d− 1), sedangkan
dengan cahaya terus-menerus dan pemberian pakan pada larva memiliki efek yang negatif
pada pertumbuhan (29 μm d− 1) dan kelangsungan hidupnya (13%). Kelangsungan hidup
tertinggi didapat dari 12 jam pencahayaan dan 24 jam pemberian pakan,
kelangsungan hidupnya mencapai 44%.
Kata Kunci
Jadwal pemberian pakan, Photoperiod, Pertumbuhan, Strombus, Larva
1. Introduction
Although there is considerable
knowledge of the general life history and larval culture ofStrombus gigas (Linné
1758), the species Strombus pugilis has
rarely been studied (Bradshaw-Hawkins, 1982, Brito-Manzano et al., 1999 and Brownell, 1977). The fighting conch, S. pugilis, is one
of six species of conches distributed throughout the Caribbean inshore waters
on sandy bottoms ( Berg, 1976, Berg et al., 1983 and Brownell and Stevely, 1981). Conches are an important source
of protein of great economic and cultural significance to the inhabitants of
the Caribbean and Yucatan Peninsula, Mexico regions. Conches are considered new
marine aquarium organism. Aquacultured specimens are the alternative to wild
caught conches and it is the goal to ensure the future as well as conserve the
natural populations. For this reason why it is important research and produce,
through aquaculture, for the marine aquarium trade. Aquarium prices for conches
are in the range 4.5 to 15 Euros for a unit in the South East of Florida,
Brazil, Hawaii and West Indies. It is important to develop aquaculture
techniques to enhance production through private and public mariculture.
However, the use of this for the production of conch seeds have been proposed
as a basis for restoring depleted natural populations of this species, although
it has only been done for S. gigas and S. costatus ( Baqueiro-Cárdenas, 1997).
On the other hand, while studies on fisheries and mariculture are numerous,
those of specific larval preferences and the importance of feeding schedule for
the success of larviculture are limited. To maximize spat production in
hatcheries it is necessary to understand the environmental preferences of the
larvae. Optimization of these parameters and achieving the correct balance can
result in improved growth and survival rates, a reduction in the larval rearing
period and a subsequent reduction in production costs.
Little is known of the larval
development, dispersal, nutrition, photoperiod and settlement of S. pugilis. The
effect of photoperiod on growth has been studied in molluscs, but with
contradictory results. Dodd (1969) reported that light had no effect on
the absolute rate of growth measured as calcium deposition in Mytilus edulis and M. californianus, although a reduction in shell growth
was noted. Strömgren
(1976) also showed that darkness encouraged
length growth of M. edulis, and Strömgren
(1976) found that Modiolus modiolus increased its growth rate
significantly during continuous darkness, while no such effect was found for Cerastoderma edule. Nielsen (1985) has shown that in juvenileM. edulis grown
in dim day-light there is a linear relationship between shell length growth and
ash-free dry weight growth. Barilé et al. (1994) found that larvae of S. gigaspresented
strong positive phototaxis and negative geotaxis during early stages and that
positive phototaxis decreased as a function of age. No information is available
on the effects of photoperiod on Strombus larvae.
The goal of this work was to determine the effect under photoperiods and
feeding schedules on growth, settlement and survival on larvae of S. pugilis in laboratory culture.
2.
Materials and methods
The
fertilized egg mass used for the experiment was collected in May, June and July
at Seyba Playa, in Yucatan Peninsula Mexico. It was collected by scuba diving
from a depth of 4 m from under a female conch to ensure species identity
and egg freshness. Afterwards, it was transported to the laboratory, where
epibionts and sand particles were removed. The egg mass was cleaned with 10-μm
filter and UV-sterilized seawater. The cleaned egg mass was placed over a
300 μm mesh and kept immersed in a 25-L aquarium with seawater filtered
through 2 μm cotton filters and UV-sterilized. Temperature was maintained
at 29 ± 1 °C. Each month one single egg mass was used to avoid
variability among egg masses from different parents.
For the three experimental cultures,
larvae were reared according to the method described by Brito-Manzano
et al. (1999). Larvae were reared from hatching to
settlement in three photoperiods (0 L, 12 L and 24 L) and two
feeding schedules (12 F and 24 F), as shown in Table 1.
For sets A (0 L/12 F) and B (12 L/12 F) the change of water
was 12 h each, while for the sets C (0 L/24 F), D
(12 L/24 F) and E (24 L/24 F) each 24 h. For each set,
there were three replicates. Larvae were stocked in 4-L container with a
density of 200 larvae L− 1. Larvae
of each treatment were fed of fresh algae Tetraselmis suecica at
a concentration of 1000 cell mL− 1 (Garcia
Santaella and Aldana Aranda, 1994). There was a single
addition of food at the beginning of each feeding schedule. Every two days, 30
larvae were collected at random from each replicate for the observation of
growth. Three light bulbs with tungsten filament (Phillips 60 w), placed above
water surface, were used as light source. The light was turned on at 06:30.
Darkness was obtained by covering the container with black plastic covers. Each
morning veligers were transferred to new containers with fresh seawater
filtered through 10 and 2 μm cotton filters. It took approximately
5 min for these procedures; therefore, 0 light had a five minutes light
phase per day.
Table 1.
Feeding schedules and
photoperiods used for larvae culture of Strombus pugilis.
Photoperiods
(Light hours)
|
Feeding schedules
(h)
|
|
12
|
24
|
|
0
|
0/12 (set A)
|
0/24 (set C)
|
12
|
12/12 (set B)
|
12/24 (set D)
|
24
|
–
|
24/24 (set E)
|
For each month, growth was assessed
recording increments of siphonal length. Larvae were measured using a compound
microscope with a calibrated ocular micrometer to the nearest 0.10 μm.
Differences between means were tested by ANOVA and Tukey tests. Significance
was assumed when P < 0.05. With the target of not altering
the results of survival, a subsamples of 10 larvae were sampled at random every
48 h from each of three replicates (n = 30).
Growth rate was calculated according to Garcia Santaella and Aldana Aranda
(1994) as:
average growth rate in μm d− 1 = (average
shell length at the end of the experiment − average shell length at
the beginning)/total growth period in days. Settlement was examined by
reabsorption of velar lobes, outward migration of eyes, foot and adult
operculum claw appears and swim–crawl behavior. Survival in the culture for the
three months was calculated using the number of living larvae at the beginning
and end of the experiment. ANOVA and Tukey tests were used to determine if
settlement and survival were significantly different for veligers in different
treatments. Significance was assumed when P < 0.001 for settlement and P < 0.0001
for survival.
3.
Results
At 29 days of
culture the larvae of May and June were competent for settlement, 100% of the
larvae, was recorded in sets C and D while sets A, B and E had only 97%, 80%
and 84%, respectively had settled at 31 days (Table 2).
Settlement does not exhibited significant differences between months (P < 0.001).
Table 2.
Settlement, average
size at settlement, growth rate, larval survival for each feeding schedule and
photoperiods conditions for the veliger of S. pugilis, fed T. suecica and reared at 29 ± 1 °C,
for three months.
Treatment
A
|
Treatment
B
|
Treatment
C
|
Treatment
D
|
Treatment
E
|
|||||||||||||
May
|
Jun
|
Jul
|
May
|
Jun
|
Jul
|
May
|
Jun
|
Jul
|
May
|
Jun
|
July
|
May
|
Jun
|
Jul
|
|||
Settlement
|
Days
|
31
|
30
|
31
|
31
|
31
|
31
|
29
|
29
|
28
|
29
|
29
|
30
|
31
|
31
|
31
|
|
%
|
97n.s
|
97n.s.
|
96n.s.
|
80*
|
80*
|
76*
|
100n.s
|
100n.s.
|
98n.s.
|
100n.s.
|
100n.s.
|
99n.s.
|
83*
|
85*
|
83*
|
||
Growth
|
Average
(μm) |
933
|
937
|
933
|
1023
|
1028
|
1025
|
1496
|
1501
|
1499
|
1117
|
1117
|
1119
|
912
|
910
|
913
|
|
Rate
(μm d− 1) |
23n.s
|
24n.s.
|
23n.s.
|
26n.s.
|
27n.s.
|
26n.s.
|
41*
|
42*
|
42*
|
22n.s.
|
22n.s.
|
23n.s.
|
29n.s.
|
29n.s.
|
29n.s.
|
||
Survival
|
%
|
26*
|
25*
|
25*
|
34*
|
34*
|
34*
|
22*
|
20*
|
22*
|
44*
|
46*
|
44*
|
13*
|
10*
|
11*
|
|
The asterisk indicates
significant difference between treatments, n.s. indicate no significant
difference.
Fig. 1 shows that average shell
length was reduced in larvae in sets A (0 light conditions and 12 h
feeding) and E (24 light and feeding conditions) with 912 and 933 μm (P < 0.001), respectively, in the
three months evaluated, otherwise in set C (under 0 light conditions and
24 h feeding) growth was significantly higher with an average of
1499 μm (P < 0.001).
Fig. 1.
Curves of average growth of siphonal shell length of the larvae of Strombus pugilis reared under five different
treatments with three photoperiods and two feeding schedules. L, hours of light
and F, hours of food. a) Experimental larval culture, May; b) experimental
larval culture, June; and c) experimental larval culture, July. Each average
point was established with n = 30
larvae measured.
Settlement day and percentages,
average size at settlement, growth rates and survival for cultures realized in
May, June and July are shown in Table 2,
for the five treatments. The ANOVA and Tukey tests showed significant
difference (P < 0.001). Larvae in sets B (12 light
conditions and 12 h feeding) and D (12 light conditions and 24 h
feeding) had an average growth rate of 26 and 22 μm d− 1, respectively. Larvae under 0 light
conditions and 24 h feeding (set C) showed the fastest growth rate during
the experiment and it was significantly higher than for the others sets, but
survival tended to be lower compared with other treatments. The highest
survival was attained under set D with 44%, which was significantly higher than
for set E and C with 11 and 21 %, respectively. ANOVA test showed a significant
difference between treatments (P < 0.0001).
Moreover ANOVA does not demonstrate a significant difference between months.
4.
Discussion
The three experimental
series demonstrated that the optimal photoperiod and feeding schedule for
maximal growth of larvae of S. pugilis was
0 L/24 F. The darkness had a direct influence on growth with
continuous feeding, but with a lower survival. Shell lengths of larvae were
consistently lowest for treatments A and E regardless of culture month. The
growth of the larvae presented the same behavior reported by Lucas
et al. (1986) with
larvae of Mytilus edulis, and Garcia
Santaella (1992) and Garcia
Santaella and Aldana Aranda (1994) with larvae of S. gigas. These
authors reported endotrophy and exotrophy phases in the growth; the first
depends directly on the egg reserves and exotrophy phase depends directly on
the quality and quantity of food supplied and the effect of environmental
factors. In this study, the growth of 0–15 days did not differ between
treatments compared to the growth obtained during 16–31 days. The effect
of photoperiod and feeding schedule were more evident after 21 culture days,
when larvae exhibited a positive geotropism behavior. This behavior was
observed by Gorrostieta-Hurtado
et al. (2009) with
the abalone, Haliotis corrugata. Brito-Manzano
and Aldana-Aranda (2004) studied 17 developmental
characteristics, growth and survival of S. gigaslarvae for several months (March to
September). They found for all larvae reared during these months that developmental
characteristics were the same. The only differences found were in rate of
kinetic development. It was attributed to the differences in biochemical
composition of the egg masses ( Brito-Manzano,
2004). Brito-Manzano
et al. (2006) did
not found significant differences in settlement and survival between months
with larvae from S. gigas during
May–July (1997–2000) .
In routine laboratory
and hatchery techniques Strombus larvae
are fed for 24 h with a change of water after 24 h. In Strombus larvae, growth rates and time to
settlement are known to vary with temperature, nutrition and density of
cultures ( Boidron-Metairon, 1990 and Davis, 1994). For
instance, the onset of settlement for S. pugilis larvae
can occur in between 27 and 31 days, Bradshaw-Hawkins
(1982) reported
settlement in 30–31 days and a maximal size of 1180 μm, while Brito-Manzano
et al. (1999) obtained
the settlement in 30–31 days and a maximal size of 1022 μm, in the
same conditions of larval density, algal concentration, culture containers and
temperature. In contrast, Brito-Manzano
et al. (2000) reported
for S. pugilis, fed
larvae for 12 h during daylight reached settlement in 29–31 days and
a maximal size of 1024 μm. Results of growth were obtained in this study:
larvae fed for 24 h in darkness reached the settlement in 27–29 days
with a maximal size of 1496 μm, while larvae fed at daylight for 24 h
reached it in 31 days and a maximal size of 912 μm. For settlement
and survival, the highest yield was obtained with 12 h light and 24 h
feeding. Treatment of 12 h light and 12 h feeding resulted in a greater
number of days to reach the highest yield in settlement and survival. Worth
larvae feed continuously as you get a reduction of about 48 h to reach the
settlement, increased by 20% the gain of the population that settled and the
survival increased by 8%. Even though the treatment 12 h light and
24 h feeding was the best, the gain is only 7% in production of seed than
treatment 12 h light and 12 h food. Several authors have found that
photoperiod affects growth; Nielsen
(1985) has
shown that in juvenile Mytilus edulis grown
in dim day-light, there is a linear relationship between shell length growth
and ash-free dry weight growth, also within a short time scale. This implies
that there may be a dark enhancement effect also for tissue growth. Nielsen
and Strömgren (1985) with M. edulis larvae showed clearly that as long as
food is not severely limiting, growth is enhanced by darkness. They found that
growth in darkness was 20% greater than that in natural sunlight. Light
probably reduces growth rate by inhibiting ingestion rate. Salaün
(1994) found
that larvae of Pecten maximus ate
less food during daylight and less in the superficial layer of the water in
comparison with larvae in deep water. Hurley
et al. (1987) studied
the formation of growth lines in sea scallop shells larvae (Placopecten magellanicus) and found that photoperiod
did not affect the rate of shell deposition. These authors suggested an
endogenous control of growth-line formation in this bivalve. In this study,
0 L/24 F conditions encouraged settlement and growth, while in
24 L/24 F, growth and settlement were reduced. Continuous light
caused negative effects on larval survival (11%). These results could be
related with strong positive phototaxis and negative geotaxis present during
early stages of Strombus larvae
described by Barilé
et al. (1994). Gorrostieta-Urtado
et al. (2009) studied
postlarvae of the abalone Haliotis corrugata under
two illumination conditions (constant light and darkness) found highest grazing
rate, survival and growth in darkness than in constant light. Higher grazing
and growth rates in darkness reinforce the hypothesis that the nocturnal habits
of abalone develop soon after metamorphosis. In this work, light made the
difference. The optimal photoperiod and feeding schedule for maximal growth of
larvae of S. pugilis was
0 L/24 F and the lowest was 24 L/24 F. Such was also
observed for settlement and survival. It would be interesting to further study
positive phototaxis and negative geotaxis during early stages and positive
geotaxis in the latest stages in S. gigas larvae
to ameliorate the culture larvae. The results obtained during this
investigation strongly indicated that photoperiod itself is of importance for
development, growth and survival of larvae.
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