Corresponding author: Vlastimil Stejskal ( stejskal@frov.jcu.cz ) Academic editor: Predrag Simonović
© 2021 Vlastimil Stejskal, Jan Matousek, Roman Sebesta, Joanna Nowosad, Mateusz Sikora, Dariusz Kucharczyk.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Stejskal V, Matousek J, Sebesta R, Nowosad J, Sikora M, Kucharczyk D (2021) Stocking density effect on survival and growth of early life stages of maraena whitefish, Coregonus maraena (Actinopterygii: Salmoniformes: Salmonidae). Acta Ichthyologica et Piscatoria 51(2): 139-144. https://doi.org/10.3897/aiep.52.64119
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The maraena whitefish, Coregonus maraena (Bloch, 1779), is often considered a suitable candidate for intensive aquaculture diversification in the EU. However, only a few such farms in Europe are in operation. Rearing this species in recirculating aquaculture systems is a recent innovation, and optimisation is necessary to standardise aspects of larviculture. This 30-day study investigated the effect of stocking densities of 25/L, 50/L, 100/L, and 200/L on the survival and growth of maraena whitefish larvae in a recirculating aquaculture system. The four groups of larvae (initial weight = 7.4 ± 0.1 mg; initial total length = 13.0 ± 0.1 mm) in three repetitions were reared in a recirculating system. Larvae were fed fresh live brine shrimp metanauplii every 3 h at a rate converted to larval stocking density. After the experiment, 10 larvae from each tank (30 of each density group) were weighed on a digital microbalance (ABJ 220-4M KERN, Germany, readout = 0.1 mg) and measured manually on images taken with Leica MZ16 A stereomicroscope and a digital colour camera with 5-megapixel resolution for Leica DFC420 Image Analysis. No significant differences in final body weight, total length, size heterogeneity, condition factor, or survival were found among treatments (P > 0.05). The highest non-significant survival rate and growth parameters were observed in larvae reared at 25/L. On the contrary, it is possible to rear maraena whitefish larvae at high stocking density without any subsequent negative consequences for growth and survival. As no significant differences in any evaluated parameter were observed between groups of larvae at the highest and lowest stocking density, we conclude that it is possible to rear maraena whitefish larvae at high stocking density (and 200/L) without any subsequent negative consequences for growth and survival.
coregonids, fry, growth metrics, larviculture, recirculation systems
The maraena whitefish, Coregonus maraena (Bloch, 1779), is a promising species for inland freshwater aquaculture throughout east-central Europe (
Excessively high density can produce a stress response, particularly increased plasma cortisol level (
In Europe, the initial rearing of coregonid larvae in intensive indoor tanks is usually practised with stocking densities ranging from 5 to 100 larvae/L (
The optimal stocking density needs to be determined for each fish species and developmental/reproductive stage to facilitate survival and growth and enable efficient management to maximise production and profitability, as well as to provide proper conditions for fish. Information on stocking density effects on maraena whitefish larvae growth performance and survival is scarce. The goal of the presently reported study was to determine whether stocking density affects the survival and growth of maraena whitefish larvae reared in a recirculating aquaculture system (RAS).
Maraena whitefish were obtained from in the Szczecin Lagoon (the River Odra estuary), north-western Poland. The broodstock comprised 120 fish at a 1:1 sex ratio. Gametes of three-year-old 60 females (mean weight, 800.4 ± 80.1 g, mean ± SEM; mean total length, 30.2 ± 1.1 cm) and three-year-old 60 males (650.5 ± 49.7 g, mean ± SEM; mean total length, 26.4 ± 0.9 cm) were stripped manually (no hormone stimulation) by commercial fishermen in December 2016 shortly after fish capture and transported to local hatcheries for fertilization and incubation. Eggs (100 mg) were fertilized with 0.5 mL of milt mixed with 50 mL of hatchery water and incubated at the ambient water temperature of the river (2–3°C) with initial water inflow 3 L/min, oxygen saturation to 90%, and pH near 7.0. In February 2017, the eggs were taken to the Department of Lake and River Fisheries (Olsztyn, Poland) where they were distributed among five 8-L Zug jars (n = ~150 000 eggs/jar) in a recirculating system and incubated at 3.0–3.5°C with water inflow 3 L/min, oxygen saturation to 90%, and pH near 7.0. In total, ~750 000 eggs were incubated. After 60 days, eggs were transferred to the second set of 8-L Zug jars and incubated at 8–9°C to accelerate development and hatching. After 5 days, the temperature was increased to 10°C for mass hatching. Hatching success was estimated at 90%, and about 675 000 larvae were available for the experiment. Hatched larvae swam across to a tank (total volume 1 m3) underlain with 0.2 mm mesh. After 24 h, larvae were transferred to tanks in the RAS.
Four groups of larvae in three replicates were transferred to the experimental aqua system consisting of twelve 2 L aquaria, 96 × 154 × 200 mm. The recirculating system (2300-L total water volume) included a series of filtration sections (total biofilter volume 1500-L), a settling tank (500-L water volume). Thirty fish were weighed and measured to obtain the initial values for weight and length. Maraena whitefish larvae (initial weight, 7.4 ± 0.1 mg, mean ± SEM; initial total length, 13.0 ± 0.1 mm) were placed into each aquarium at stocking density of 25/L (S25), 50/L (S50), 100/L (S100), and 200/L (S200). A biomass by litre (g/L) was 0.185 (S25), 0.370 (S50), 0.740 (S100), 1.480 (S200). A total of 2250 larvae were used in the experiment.
The oxygen level, water temperature, and pH were checked daily at 0800 and 1600 h. The pH range was monitored using an OxyGuard H04PP Handy pH meter (OxyGuard International, Denmark). The initial temperature without supplemental heat was 10°C. Water temperature ~19°C was regulated by a HAILEA HC-1000A cooler (China). The temperature was gradually elevated from 10°C to 19°C (3°C/day). Oxygenation was maintained using two SICCE Syncra 5.0 pumps (5000 L/h) (Italy). Ammonia, nitrate, and nitrite concentrations were analysed using HACH, LCK 304, LCK 339, LCK 341 (Germany) with a HACH DR5000 spectrophotometer (Germany). Disinfection used a 30 W UV MCT Transformatoren GmbH steriliser (Germany). NaCl was added at 1 g/L weekly to maintain a 16:1 chloride:nitrogen ratio. A constant inflow of 0.4 L/min was ensured. Dead larvae were removed and counted during daily cleaning. The level of organic matter remained low. A low CO2 level was maintained via aeration and keeping alkalinity stable. During the 30-day trial, basic physico-chemical parameters were following: temperature = 19.1 ± 0.0°C, pH = 8.7 ± 0.0, O2 saturation = 85.8 ± 0.9%, O2 concentration = 7.9 ± 0.1 mg/L, NH4+ = 0.1 ± 0.0 mg/L, NO2 = 0.8 ± 0.1 mg/L, NO3 = 21.2 ± 5.4 mg/L.
Larvae were fed fresh live metanauplii of brine shrimp, Artemia salina (Ocean nutrition, HE > 230 000 NPG, Belgium) (20–24 h old, 0.4–0.5 mm) four times daily at 3 h intervals during the light phase (0830 to 1730 h). The feeding level was fixed to the range of 500–700 Artemia sp. metanauplii per fish per day at a rate converted to larval stocking density (Table
Concentration of brine shrimp (Artemia salina) fed to larvae of maraena whitefish, Coregonus maraena (Bloch, 1779) in a 30-day trial.
Group | Whitefish stocking density | Artemia feeding dose | ||
---|---|---|---|---|
[larvae/L] | [larvae/2L] | [mL/L] | [mL/2L] | |
S25 | 25 | 50 | 2.5 | 5 |
S50 | 50 | 100 | 5.0 | 10 |
S100 | 100 | 200 | 10.0 | 20 |
S200 | 200 | 400 | 20.0 | 40 |
R opt = 4.89W–0.27
where Ropt = optimal daily feeding level, W = body weight [g].
After the experiment, 10 larvae from each tank (30 of each density group) were weighed on a digital microbalance (ABJ 220-4M KERN, Germany, readout = 0.1 mg) and measured manually from images taken with Leica MZ16 A stereomicroscope and a digital colour camera with 5-megapixel resolution for Leica DFC420 Image Analysis.
A sample size of ten larvae per tank, 30 larvae per treatment, was used as in a number of studies (
The survival rate (SR), size heterogeneity (SH), and condition factor (K) and specific growth rate (SGR) were assessed as follows:
SR (%) = 100 × (Nf/Ni)
in which Ni and Nf = initial and final number of larvae, respectively;
SH (%) = 100 × (SD/Wm)
in which SH = size heterogeneity; SD = mean standard deviation of weight of 10 randomly selected larvae/tank; Wm = mean weight [mg] of 10 larvae/tank.
K = 100 000 × W × (TL3)–1
in which W = mean weight [g] of 10 larvae/tank; TL = mean total length [mm] of 10 larvae/tank
SGR (%) = 100 × [(lnWt – lnW0)/d]
in which Wt and W0 are final and initial weight of larvae, respectively [g]; d = duration of the experiment [days].
Statistical analyses were performed using STATISTICA 12.0 (StatSoft, Praha, Czech Republic). Data are presented as mean ± SEM. The effects of stocking density on W, TL, SR, K, SH, and SGR were analysed by one-way ANOVA with stocking density as a fixed variable. Differences were considered significant at P < 0.05. Prior to ANOVA, SR, K, SH, and SGR were arcsine-transformed. All data were tested for homogeneity of variance using the Cochran, Hartley, and Bartlett test, and for normality with the Shapiro–Wilk normality test. The parametric Tukey test was used for assessing differences among groups in W, TL, SR, SH, K, and SGR (Table
One-way ANOVA results for the factor stocking density on total length (TL), body weight (W), size heterogeneity (SH), condition factor (K), survival rate (SR), and specific growth rate (SGR) of larvae of maraena whitefish, Coregonus maraena (Bloch, 1779).
Parameter | Source of variation | SS | DF | F | MS | P |
---|---|---|---|---|---|---|
TL | SD | 0.9 | 3.0 | 0.3 | 2.3 | 0.2 |
W | SD | 466.3 | 3.0 | 155.4 | 2.7 | 0.1 |
SH | SD | 22.7 | 3.0 | 7.6 | 0.2 | 0.9 |
K | SD | 0.0 | 3.0 | 0.0 | 2.2 | 0.2 |
SR | SD | 3.6 | 3.0 | 1.2 | 0.2 | 0.9 |
SGR | SD | 0.0001 | 3.0 | 2.1 | 0.00005 | 0.2 |
At the conclusion of the trial, no significant (P>0.05) differences among treatments were observed in SR, W, TL, SH, K, or SGR (Table
Effect of stocking density on growth and survival of larvae of maraena whitefish, Coregonus maraena (Bloch, 1779), in a 30-day growing trial.
Group | SR [%] | TL [mm] | W [mg] | SH [%] | K | SGR [%] |
S25 | 92.7 ± 2.4 | 30.7 ± 0.3 | 147.9 ± 5.8 | 22.5 ± 4.3 | 0.51 ± 0.01 | 0.50 ± 0.003 |
S50 | 91.3 ± 1.5 | 30.4 ± 0.2 | 135.7 ± 1.6 | 20.3 ± 3.6 | 0.48 ± 0.01 | 0.49 ± 0.001 |
S100 | 91.33 ± 1.1 | 30.4 ± 0.1 | 135.1 ± 3.5 | 21.1 ± 4.9 | 0.48 ± 0.00 | 0.49 ± 0.003 |
S200 | 91.8 ± 1.0 | 30.0 ± 02 | 131.3 ± 5.2 | 18.7 ± 2.3 | 0.49 ± 0.01 | 0.49 ± 0.004 |
The fact that growth–weight parameters did not differ significantly means that maraena whitefish growth was not influenced by stocking density at the tested levels. Slightly lower (non-significant) growth was found with increasing stocking density. It is important to sustain uniformity of fish size in aquaculture (
Stocking density can influence mortality rate, with survival often negatively correlated with stocking density as shown for silver perch, Bidyanus bidyanus (Mitchell, 1838) (see
Stocking density has been reported to be an important factor in fish growth (
No significant differences in any evaluated parameter were observed between groups of larvae at the highest and lowest stocking density. It is possible to rear maraena whitefish larvae at high stocking density with no subsequent negative consequences for growth and survival. This study examined fry and early-stage larvae, but a further study, focusing on juvenile and adult maraena whitefish, is warranted. The effects of stocking density on stress hormone response, body composition, and haematological and biochemical parameters of maraena whitefish should be studied.
The study was financially supported by the Ministry of Agriculture of the Czech Republic and NAZV project (QK1810296).