2. Materials and methods
Pueruli of J. edwardsii were collected from experimental collectors located at Bicheno on the east coast of Tasmania. They were maintained in a recirculating system
at 188C before the commencement of the trials. Trials were conducted in a flow-through system consisting of 4 = 280-l reservoir
Ž .
tanks and 12 = 33-l black fibreglass tanks diameter 430 mm, depth 300 mm . Incoming water was filtered to 400 mm before entering the reservoir tanks. The reservoir tanks
were maintained at precise temperatures of 18, 20, 22 or 248C using 1.2–2.4 kW titanium heaters. Temperatures in the tanks were monitored at 10-min intervals by a
Ž .
Vemco minilog data logger TR data loggers . Temperatures were also manually
checked each day. Each heated reservoir tank was connected to three replicate experi- mental tanks. The flow to each tank enabled a complete water exchange every 30–40
minutes. An 8-h light:16 h dark photoperiod was maintained with light intensity of 1 mmol s
y1
m
y2
at the water surface. Ž
. Thirteen post-pueruli initial mean weight SE s 0.99 0.01 g were stocked into
each 33-l tank and they were temperature-acclimatised from 188C over 5 days before the first weight measurement. During the first week after the initial weight measurement,
mortalities were replaced with temperature-acclimatised animals of similar weight. These mortalities were assumed to be due to stresses associated with handling and were
not included in the final mortality data.
The juvenile lobsters were fed once daily with either freshly opened mussels cultured Ž
. Ž
. Mytilus edulis planulatus or dry growout pellets for penaeids Penaeus japonicus .
Previous studies indicated that fast growth and high survival could be achieved on a Ž
. mixed diet of fresh mussels and dry pellets Crear et al., 1999 . An estimation of daily
food consumption was obtained via a visual estimate of food remaining in the tanks before morning cleaning. Food was provided slightly in excess and was based on the
previous days’ consumption. Feed consumption was calculated on dry matter consumed per wet weight biomass and expressed as a percentage of wet lobster body weight per
day. Samples of mussels and the dry diet were dried to give an estimate of moisture content. To take into account mortalities, the number of lobster days of feeding was
Ž .
calculated based on survivors at each weighing and used to calculate daily weight gain Ž
. and feed intake for each lobster. Food conversion ratios FCR were calculated as the
Ž . estimated dry weight of feed consumed per day g per lobster wet weight increase per
Ž . day g .
Lobsters were weighed to the nearest 0.01 g at days 0, 29, 59 and 92. Animals were dried on absorbent paper for 30 s to remove excess water before weight measurement.
Ž .
Ž .
Specific growth rate SGR , percentage weight gain WG , moult increment and moult interval were used to evaluate growth. Moult interval and moult increment
calculations were based on data collected between the second and third weight measure- ments, as there were no mortalities during that period. These parameters were defined
Ž .
Ž as: SGR s ln final weight y ln initial weight
100rnumber of days; WG s final .
weight y initial weight 100rinitial weight; moult increment s mean WGrmean
moults per lobster; moult interval s number of daysrmoults per lobster.
At the completion of the growth trial, lobsters were starved for a period of 60 h before oxygen consumption trials at the experimental temperatures. The experimental
system described above was supplied with 0.2 mm filtered seawater. A total of 48 Ž
. animals 12 per treatment in the intermoult stage were selected and weighed and placed
Ž .
into brown glass BOD bottles 755 ml . Animal weights ranged between 2.4 and 7.8 g. Ž
. Twelve respirometers three per treatment had no animals and served as controls.
The respirometers were immersed in the experimental tanks that acted as temperature baths. High oxygen saturation levels within the respirometers were maintained during
the 16-h acclimatisation period by providing flow-through filtered seawater. An initial oxygen concentration measurement was recorded before the respirometers were sealed.
Oxygen concentration was recorded after 60 min. The respirometers were then provided with flow-through water for 3 h to reoxygenate the water before the experimental
procedure was repeated. During the measuring period, the oxygen concentration did not
y1
Ž
y1
. fall below 4.0 mg l
. Standard oxygen consumption M mg min
was determined
O
2
by the equation: P
y P V
Ž .
O O
2 i 2 f
M s
O
2
T Ž
y1
. where P
and P are the final and initial oxygen levels, respectively mg l
, V is
O O
2 f 2 i
Ž .
the volume of water in respirometer ml and T is the elapsed time in minutes. At the completion of the oxygen consumption trial, 20 ml water samples were taken
Ž from the respirometers and stored at y188C until total ammonia nitrogen TAN s NH
3 q
. q NH
analyses were conducted. Water from the control respirometers was used to
4
determine initial ammonia concentration. TAN was measured using the phenol–hypo- Ž
. chlorite method using procedures outlined by Parsons et al. 1984 . Ammonia excretion
Ž
y1 y1
. TAN y mg TANrg
h was determined from the following equation:
TAN y TAN V
Ž .
f i
TAN s W T
where TAN is the ammonia as nitrogen in the sample at the end of the measuring
f
period in mg l
y1
, TAN is the ammonia as nitrogen in the sample at the beginning of the
i
sampling period in mg l
y1
, V is the volume of water in the container in litres, W is the weight of the lobster in grams and T is the time of the measuring period in minutes.
Q values for oxygen consumption and ammonia excretion were determined using
10
the following equation:
10rT yT
2 1
M
2
Q s
10
ž
M
1
where M and M s oxygen consumption at temperatures T and T , respectively.
1 2
1 2
All data were tested by ANOVA with comparisons of means following ANOVA using the Scheffe post-hoc test. Survival data were arcsine-transformed before analysis
Ž .
Sokal and Rohlf, 1995 . The growth and survival data were plotted and curvilinear regressions were fitted to obtain the temperature response curves. Least-squares regres-
sion was used to assess relationships between body weight and oxygen consumption or
ammonia excretion. Regressions were tested for significance by analysis of variance. The optimal response to temperature was predicted as the upper or lower asymptote of
Ž .
the best-fitting quadratic response curve Lellis and Russell, 1990 .
3. Results
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