Reproductive performance of
carpet-shell clam, Ruditapes decussatus, under experimental
conditions
Aquaflow Technical Leaflet 2002-109
European Network for the Dissemination of Aquaculture
RTD Information (Q5CA-2000-30105) and previously FAIR-3837, URL: http://www.aquaflow.org/
The influence of food ration and water flow on the
rate of gonadal development and spawning during hatchery conditioning of the
carpet-shell clam was assessed. Broodstock was conditioned for spawning at
20ºC in sand-filtered seawater enriched with a diet of Skeletonema
costatum over a 12-week period. Three dietary rations (dry weight of
algae/initial dry meat weight of clams) at three flow rates were tested: 6%
at 11/min (S1), 3% at ½ l/min (S½) and 1.5% at ¼ l/min (S ¼). An unfed
group (U) was used as control. The condition index, gonadal development and
gross biochemical composition (total lipids and glycogen content) were
examined with a four-week interval. Attempts to induce the clams to spawn
were made after 12 weeks.
The S1 and S½ treatments had the higher condition
indices at the end of the experiment (170.77 and 170.30 respectively)
compared with S ¼ and U treatments (110.77 and 60.80 respectively). The
glycogen appears to be a suitable indicator of the reproductive state of the
animals: each time the glycogen values were close to zero, the clams spawned
spontaneously and then a new phase of renewed gametogenesis occurred.
Attempts to induce the clams to spawn should have been made much earlier. At
the end of the experiment all clams spawned except the unfed control group.
The number of eggs (in millions per female ranged from 0.344 to 5.538 (S1),
from 0.390 to 4.961 (S½) and from 0.175 to 2.335 (S¼), with a mean value
of 2.4426, 2.237 and 1.346 million respectively.
The great similarity of the obtained results for
treatments S1 and S ½ for all the parameters studied can result from a
better use of the feed in S ½, due to a slower water flow rate in the
tanks. The percentage of particles filtered from the water increased as the
flow rate decreased (45% for S1, 73% for S ½ and 86% for S ¼), so the
number of algae filtered were not a real reflection of the rations fed,
expressed as percentage. This study seems to indicate that the circulation
rate has a significant impact in the optimisation of microalgae diets that
are provided during the conditioning period.
* This work is a thesis done by Alexandre Dâmaso in
the CICEM of Huelva, Spain, in cooperation with the CRIPA and the Faculty of
Sciences of Lisbon, under the joint supervision of Dr. Royo Rodriguez, Dr.
Moreno and Dr. Matias.
For more information, contact
MATIAS
Domitília
CRIPA-IPIMAR
Av. 5 de Outubro
8700 Olhão
Portugal
Phone : + 351 289 700500
Fax : +351 289 700535
e-mail :
amatias@ualg.pt