conclude that under generally favourable rearing conditions, egg size has no direct implications for larval survival of Siberian sturgeon. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Siberian sturgeon; Acipenser baeri; Larvae; Mortality; Growth; Egg size
1. Introduction
Sturgeon fingerling production is considered to be one of the most difficult phases of hatchery rearing. Egg size and development may affect their quality, ability to produce
viable larvae, and to some extent directly determine growth and survival of young fish Ž
. Heming and Buddington, 1988; Kjorsvik et al., 1990 . Under artificial conditions, once
larvae hatch from the egg and deplete their intraembryonic yolk sac reserves, their survival depend on multiple factors, such as the nutritional input, rearing system design
Ž .
and hatchery management Conte et al., 1988 . Early life stages of development are some of the most important phases of fish development, which include the replacement
Ž of embryonic adaptations and functions e.g., yolk sac nutrition and cutaneous respira-
. Ž
. tion
by definitive ones e.g., exogenous feeding and branchial respiration . Such
Ž adaptations alter the relationship of the developing fish with the environment Dettlaff et
. al., 1993 , and these changes can directly affect growth and survival of young speci-
mens. Mortality of acipenserids during embryonic and larval development is of considerable
Ž importance Buddington and Christofferson, 1985; Gisbert and Williot, 1997; Bardi et
. al., 1998 . As a result, substantial efforts were focused on the early life developmental
stages of this group of fishes in order to understand how to increase their survivorship and improve hatchery efficiency. While there are several studies on growth and survival
Ž of Siberian sturgeon larvae under different experimental conditions Evgrafova et al.,
1982; Semenkova, 1983; Dabrowski et al., 1985; Charlon and Bergot, 1991; Gisbert and .
Williot, 1997 , little information is available on larval mortality and whether larger egg and newly hatched larvae sizes provide any advantage for growth and survival of young
fish. This information would be useful to fish farmers for estimating fingerling produc- tion, to improve rearing techniques and for hatchery management and evaluation of the
Ž .
quality of fish produced Krasnodembskaya, 1993 . The objective of the study was to examine the relationships between egg and newly
hatched larvae sizes, growth and survival of young Siberian sturgeon.
2. Materials and methods
2.1. Supply and maintenance of sturgeon larÕae This experiment was carried out in a flow-through freshwater system at the Centre de
Ž .
Recherche Aquacole C.R.E.A., Cemagref, France during 1997 and 1998. Siberian sturgeon larvae were obtained by induced spawning of 20 13–14 years old cultured
Ž .
females according to already described methods Williot et al., 1991 . Females were
Ž .
randomly chosen from those with the highest reproductive potential Williot, 1997 . In the study, parental fish of the same strain and geographic location were used to avoid
Ž .
difficulties in interpreting results Springate and Bromage, 1985 . After eliminating egg Ž
. adhesiveness Conte et al., 1988 , eggs were incubated in a closed thermoregulated and
UV-treated freshwater system at 138–158C. After 7 days of incubation, the fish hatched. Ž
In each case, a group of 2700 newly hatched Siberian sturgeon larvae 1 day .
Ž
3
post-hatch were randomly distributed into two grey plastic troughs 1.5 = 0.5 = 0.07 m .
Ž .
deep at a density of 30 larvaerl 1350 larvaertrough according to Gisbert et al. Ž
. 1999 . Troughs used in the study were approximately half the size as those used in
commercial hatcheries. Siberian sturgeon larvae were initially fed at the age of 9 days Ž
. Ž
after hatching at a feeding rate of 15 body weight BW per day Gisbert and Williot, .
1997 . This feeding rate was reduced to 10 when fish were 15 days post-hatch and Ž
. maintained at this level until the end of the rearing period 20 days post-hatch . The fish
Ž were fed a dry commercial diet
‘‘Lansy A2 and W3’’, Artemia Systems, Gent, .
Ž Belgium . Feed was delivered during the day by automatic feeders conveyor belt
. system , and only interrupted during cleaning times. Initiation of feeding was deter-
mined by means of visible indications of feeding such as distended stomachs and Ž
characteristic internal coloration associated with the dry commercial diet used Lutes et .
al., 1990 . Troughs were cleaned three times daily, at 0800–0900, 1400–1500 and 1900–2000 h
to remove uneaten food and faeces. Fish were inspected daily for abnormal behaviour Ž
. Ž .
Ž and mortality. Water temperature, dissolved oxygen DO
YSI model 57 , pH Schott .
Ž .
Gerate model CG817T , conductivity WTW LF 196 and flow rate were measured daily throughout the rearing period. Water temperature, DO, pH, conductivity and flow rate
Ž were 18.0 0.38C, 8.7 0.2 mgrl, 7.7 0.1, 367 0.6 mSrcm, 3.9 0.4 lrm mean
. S.E. , respectively. Fish were exposed to a 12-h light–dark photoperiod using
overhead fluorescent lights. 2.2. Egg size, larÕae growth and surÕiÕal measurements
Ž .
As Siberian sturgeon eggs have an ovoidal shape Dettlaff et al., 1993 , the egg Ž
. diameter mm was calculated as the arithmetical mean between the maximum and
minimum egg diameters. Egg diameter was determined under a dissection microscope Ž
. with a micrometer eyepiece Leica Wild MPS 52 . A sample of 100 eggs from each
female after stripping was used per observation. At hatch, 30 larvae were randomly sampled from each batch of eggs and their BW
Ž .
and total length TL were measured to the nearest milligram and millimeter, respec- tively. Length measurements were performed by means of a dissection microscope with
Ž
3
. a micrometer eyepiece. The volume mm
of the ellipsoidal larval yolk sac at hatching Ž
. was calculated using the following formula Heming and Buddington, 1988
V s 0.1667p LH
2
where H is the height and L is the length of the yolk sac mass. In order to measure growth during early developmental stages, a sample of 20
specimens were randomly sampled from each experimental trough every 4 days of
Ž .
rearing. TL and BW were measured. Specific growth rate SGR was calculated for Ž
. different developmental stages using the following formula Dabrowski et al., 1985
SGR day
y1
s 100 = ln W y ln W rt ;
Ž .
Ž .
t o
where W and W represent final and initial mean BWs and t the growing period in days.
t o
Mortality was recorded daily and final survival was determined by hand-counting all Ž
. surviving fish at the end of the trial 20 days post-hatch for each experimental trough.
2.3. Statistical analysis Ž
. Survival and SGR with arcsin square root transformed data of larvae, and BW, TL
and yolk sac volume of Siberian sturgeon larvae from different females were subjected Ž
. to the analysis of variance variables normally distributed, Kolmogorov–Smirnov test
Ž .
Ž .
Zar, 1974 . When a significant difference was detected P - 0.05 , the ANOVA was followed by a Turkey’s multiple-range test to identify which treatments were signifi-
cantly different. Variables were correlated initially by means of the Pearson product Ž
. moment correlation SigmaStat, 1995 . When a statistically correlationship was detected
between two variables, data were analysed by means of linear regression.
Table 1 Egg diameter and TL, BW and yolk sac volume of newly hatched larvae, and age at first feeding of Siberian
sturgeon larvae obtained from different females Data are meanS.E. of the two replicates for each treatment. Within columns, treatment means followed by
Ž .
different letters are significantly different P - 0.05 . Ž
. Ž
. Egg diameter
TL mm BW mg
Yolk sac Age of first
3
Ž .
Ž .
Ž .
mm volume mm
feeding days Female 1
3.80.1 b 12.50.3 ab
28.61.7 a 22.81.7 a
11 Female 2
3.10.1 abc 10.50.2 d
17.01.2 ik 13.01.2 k
9 Female 3
3.30.1 ac 11.70.3 b
17.81.6 fhi 15.10.8 j
10 Female 4
3.00.1 abc 10.50.2 d
14.91.7 k 12.40.8 k
10 Female 5
3.80.1 b 12.41.7 ab
26.71.7 b 23.01.7 a
11 Female 6
3.30.2 ac 11.40.3 bc
18.32.1 egh 15.60.5 ij
10 Female 7
3.70.2 b 11.70.3 b
24.61.5 m 16.61.5 gh
10 Female 8
3.50.2 abc 11.00.3 c
17.50.2 hij 18.00.7 e
10 Female 9
3.40.2 abc 11.00.2 c
17.31.1 hi 17.11.2 fg
9 Female 10
3.50.2 abc 11.00.2 c
17.00.9 il 18.20.5 cde
10 Female 11
3.50.2 abc 11.20.5 c
18.00.9 egi 18.10.9 de
10 Female 12
3.40.2 abc 11.30.3 bc
16.70.3 jkl 16.11.1 hi
10 Female 13
3.90.2 b 12.60.5 ab
27.61.6 ab 23.40.5 a
11 Female 14
3.60.2 bc 11.60.5 b
19.70.9 cd 19.01.4 bc
10 Female 15
3.50.2 abc 11.80.4 b
20.71.3 c 18.11.3 de
10 Female 16
3.50.2 abc 11.30.4 bc
18.71.8 dfg 18.90.9 b
9 Female 17
3.40.2 abc 11.30.5 bc
20.61.2 c 17.00.8 f
9 Female 18
3.50.2 abc 11.00.4 c
18.91.2 de 17.50.7 ef
10 Female 19
3.70.2 abc 11.40.4 b
22.80.9 n 19.31.3 b
10 Female 20
3.50.2 abc 11.20.4 b
20.21.1 c 17.61.1 ef
10
3. Results
