Tench (Tinca tinca L.) larvae rearing under controlled conditions: density and basic supply of Artemia nauplii as the sole food
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- Celada, J.D., Carral, J.M., Rodríguez, R. et al. Aquacult Int (2007) 15: 489. doi:10.1007/s10499-007-9116-z
After artificial reproduction of tench, larvae must be maintained indoors, and studies on rearing conditions are needed, focussing on the reduction of labour and costs. Three experiments on larvae (5th day post-hatch) were conducted for 25 days using Artemia nauplii as the sole food in order to determine basic feeding and density conditions during the first rearing period. Tench were maintained in 25 l fibreglass tanks, supplied with an artesian water flow throughout of 0.2 l min−1. Water temperature was 22.5 ± 1°C, and the photoperiod was natural. Larvae fed on a restricted amount of nauplii reached high survival rates, even with the minimum of 50 nauplii larva−1 day−1. This amount of food may be sufficient at least for the first 25 days of exogenous feeding if fast growth is not the priority, and high densities can be maintained with good survival rates (over 90% up to 160 larvae l−1 and 77% with 320 larvae l−1). When food was supplied in excess once a day, high survival rates were achieved (91–97%), without differences among the densities tested. Animals at a density of 100 l−1 reached the highest length (15.57 mm) and individual weight (46.8 mg). This growth is greater than those reported in studies feeding several times a day. It could be deduced that, while live food remains available for tench, it is not necessary to feed so frequently. Considering the relationship among the initial number of animals, final survival and growth and ration supplied, the new data reported here are useful to establish suitable stocking densities under both culture and experimental conditions.
KeywordsTinca tincaTenchLarvae rearingFeedingLive foodDensity
The tench (Tinca tinca L.) is a Eurosibirian freshwater fish and, therefore, endemic in those parts of Europe, where pond culture has developed since the Middle Ages (Steffens 1995). The species is well adapted to the climatic conditions of central and southern Europe, where it is much appreciated, creating great interest for enhanced tench culture. In this way, artificial reproduction techniques have been investigated and, at present, the major aim is the development of larvae rearing systems until these animals are large enough for grow-out or restocking purposes.
The optimal conditions at first feeding are not well established, and one of the main drawbacks is to provide food appropriate for their small mouth gape and nutritionally adequate. The studies carried out on feeding of tench larvae under natural conditions have shown selectivity in the uptake of zooplankton, which depends on the ability of swallowing live prey (Šestáková et al. 1988, 1989). Pyka (1996) concluded that tench larvae fed mostly on cladocerans and, according to Lukowicz et al. (1986), the first food organisms must be very small, from 50 up to 100 μm, and mainly consist of protozoa and rotifers such as Brachionus. Afterwards, they can ingest bigger rotifers (e.g., Asplanchna) and small Cladocera (e.g., Moina). As tench grow, Ostracoda, bigger Cladocera, Copepoda, water mites and larvae of chironomids are consumed (Steffens 1995). The study of Pyka (1997) showed that intensity of feeding is highest in morning hours.
Under controlled conditions, several authors have studied the possibility of feeding tench larvae using live food caught in ponds. Šestáková et al. (1989) noticed that at the onset of feeding, they were able to consume rotifers (Brachionus and Asplanchna) and small waterfleas (Bosmina and Chydorus). In a 25-day experiment, started the 5th day post-hatch at a density of 200 larvae l−1, Hamáčková et al. (1995) tested zooplankton smaller than 160 μm size (Rotatoria, Copepoda and Bosmina) during the first three days, whereas zooplankters smaller than 300 μm size (Rotatoria, Copepoda, Bosmina and small Daphnia) were fed to fish after this date, obtaining a final survival rate near 27%. Using the same food types with lower density (66 larvae l−1), Hamáčková et al. (1998) achieved higher survival rates (around 70%).
The studies carried out by Szlamińska et al. (1998, 1999) proved that Artemia nauplii (>400 μm) can be swallowed by larvae aged 14–22 days. Using this live food in trials carried out on 5-day post-hatch larvae at a density of 60 l−1, other researchers achieved survival rates around 85% (Wolnicki and Korwin-Kossakowski 1993) and 93% (Wolnicki and Górny 1995) after 15 days. In a 20-day trial at a density of 45 larvae l−1, Wolnicki et al. (2003) reported survival rates around 90%.
However, commercial cysts are expensive, and Artemia harvest is subjected to crisis and fluctuating prices, as Leger (1999) reported. Therefore, an estimation of the amount of nauplii required could be useful for optimising the use of Artemia. In addition, when live food is used, feeding practices call for higher labour costs that could be reduced by providing food less frequently and/or increasing stocking densities. The present study aims to establish basic feeding and density conditions during the first period of larval rearing, focusing on the possibility of reducing the amount of Artemia and labour costs.
Materials and methods
Three experiments were carried out using tench hatched under laboratory conditions by means of artificial reproduction techniques performed according to Rodríguez et al. (2004). Experiments began on the 5th day post-hatch, when tench larvae were counted one by one and distributed in semi-translucent 0.50 × 0.25 × 0.25 m fibre-glass-tanks containing 25 l of water. According to Hamáčková et al. (1998), we assumed that 5 days after hatching the larvae have a mean of 5.1 mm and 0.58 mg. The trials lasted 25 days. In order to avoid the escape of both larvae and live food, each tank was provided with a 250 μm mesh filter outlet. Aerated artesian well water was used in a flow through system of 0.2 l/min in each tank. The parameters of water quality were: pH = 8.1; hardness = 5.2°d (calcium: 32.3 mg l−1); dissolved oxygen about 9 mg l−1; total dissolved solids = 108.5 mg l−1 and total suspended solids = 39.7 mg l−1. Water temperature was maintained at 22.5 ± 1°C, and the photoperiod was natural. Freshly hatched Artemia nauplii (cysts of INVE Aquaculture Nutrition, High HUFA 430 μm, Dendermonde, Belgium) were supplied from the onset of exogenous feeding. After verifying mean hatching rates, which coincided to data provided by the supplier (250,000 nauplii g−1 of cysts), feeding ration assessment was performed from known amounts of nauplii hatched in determinate water volumes, which were distributed manually into the corresponding replicates. Feeding once a day was made in the morning, and twice a day in the morning and in the evening. Tank bottoms were cleaned twice a week.
Total length (TL) was measured with digimatic caliper (to the nearest 0.01 mm) and the individual weight was determined by means of precision balance (to the nearest 0.1 mg).
All experimental groups were in triplicate. Results were examined by analysis of variance, using the computer programme STATISTICA 4.5 (StatSoft, Tulsa, OK, USA). Arc-sine transformation of survival percentages was made. Newman–Keuls test was applied to compare difference among treatments using a significance level of P < 0.05.
7,500 tench larvae were distributed among 15 tanks with a stocking density of 20 l−1. Five feeding treatments were tested: (1) starvation—to determine the survival period with endogenous feeding, no food was supplied; (2) 50 Artemia nauplii larva−1 day−1 supplied twice a day; (3) 50 Artemia nauplii larva−1 day−1 supplied once a day; (4) 50 and 100 Artemia nauplii larva−1 day−1 in the first 13 days and from day 14 to day 25, respectively, supplied once a day; and (5) 50, 100, 200 and 250 Artemia nauplii larva−1 day−1 in the first 7 days, from day 8 to day 14, from day 15 to day 21 and from day 22 to day 25, respectively, supplied once a day.
During the first 3 days of the experiment, a sample of tench larvae was taken after food was supplied in order to observe the presence of food in the gut. At the end of the experiment, survivors were counted and the length of a fish sample (10 per replicate, 30 per treatment) was registered.
Taking into account the results obtained, the most restricted amount of nauplii (50 larva−1 day−1) was supplied twice a day to 46,500 tench larvae distributed among 15 tanks. Five density treatments were tested: 20, 40, 80, 160 and 320 larvae l−1.
At the end of the experiment, survivors were counted and the length of a fish sample (30, 45, 60, 75 and 90 per treatment of 20, 40, 80, 160 and 320 larvae l−1, respectively) was registered.
Artemia nauplii were supplied in excess once a day to 24,000 tench larvae distributed among nine tanks. Three density treatments were tested: 20, 100 and 200 larvae l−1.
At the end of the experiment, survivors were counted, and length and weight of a fish sample (30, 45 and 75 per treatment of 20, 100 and 200 larvae l−1, respectively) was registered. Specific growth rate (SGR) was expressed as SGR = 100 (lnWt − lnW0)/t, where Wt is the mean final weight, W0 is the mean initial weight, and t is the duration of experiment (days). Fulton’s coefficient (K) was used to determine the fish condition factor with K = 100(Wt/TL3).
Observation of the larval guts proved that brine shrimp nauplii were consumed starting on the first day of the experiment. In all cases, the percentage of animals with visible deformities was under 0.5%.
Survival rate and final length of tench larvae in experiment 1 (mean ± mean standard error)
Nauplii supply (n° larva−1 day−1)
Survival rate (%)
Twice a day
93.7 ± 1.3a
9.58 ± 0.7a
Once a day
93.6 ± 2.9a
9.42 ± 0.7a
Once a day
50 (1–13 days), 100 (14–25 days)
92.6 ± 3.6a
9.86 ± 0.9a
Once a day
50 (1–7 days), 100 (8–14 days), 200 (15–21 days), 250 (22–25 days)
94.5 ± 3.1a
11.16 ± 0.14b
Final length of the animals fed with the highest amount of nauplii (11.16 mm) was significantly higher than those recorded in the other treatments (around 9.6 mm).
Survival rate and final length of tench larvae in experiment 2 (mean ± mean standard error)
Stocking density (larvae l−1)
Survival rate (%)
95.4 ± 1.7a
9.48 ± 0.08a
95.4 ± 1.6a
9.46 ± 0.19a
94.0 ± 1.5a
9.49 ± 0.11a
95.0 ± 1.8a
9.24 ± 0.13a
77.0 ± 2.5b
9.25 ± 0.13a
Final length did not show significant differences among groups (around 9.4 mm).
Survival rate, length, weight, specific growth rate (SGR) and Fulton’s coefficient (K) in experiment 3 (mean ± mean standard error)
Stocking density (larvae l−1)
Survival rate (%)
96.2 ± 2.2a
15.42 ± 0.26a
44.9 ± 2.6a
17.18 ± 0.25a
1.18 ± 0.02a
97.0 ± 1.5a
15.57 ± 0.12a
46.8 ± 1.1a
17.49 ± 0.10a
1.23 ± 0.01b
91.4 ± 3.8a
13.37 ± 0.12b
28.6 ± 1.0b
15.46 ± 0.13b
1.17 ± 0.01a
Animals at a density of 100 l−1 reached the highest length (15.57 mm), individual weight (46.8 mg) and specific growth rate (17.49%), without significant differences with the density of 20 l−1. These values were lower at a density of 200 l−1. The greatest fish condition (1.23) was obtained with 100 larvae l−1.
At present, formulated dry food supplied as the only food for tench larvae seems to be unsuitable, and poor survival rates have been reported after short experimental periods (15 days) even when food was added frequently (Wolnicki and Korwin-Kossakowski 1993; Wolnicki and Górny 1995). As tench larvae were able to catch and swallow free-swimming Artemia nauplii on the first day of the experiment (5th day post-hatching), this live prey is adequate to begin external feeding. In this way, Lukowicz et al. (1986) asserted that the first food organisms must be very small (50–100 μm), and Hamáčková et al. (1995) feed on zooplankton smaller than 300 μm. Our results and others (Wolnicki and Korwin-Kossakowski 1993; Wolnicki and Górny 1995; Wolnicki and Myszkowski 1998; Fleig et al. 2001; Wolnicki et al. 2003) show that the tench larvae mouth gap and the digestive system are big enough to ingest and digest nauplii with a size of 430 μm.
Artemia cysts had to be hatched daily and the possibility of reducing the supply frequency may save on labour, overall costs and time. In experiments carried out for more than 15 days under laboratory conditions, authors add live food with high frequency and different results. In the study of Hamáčková et al. (1998), larvae at a density of 66 l−1 were fed on live zooplankton caught in ponds eight times for 14 h a day during 25 days at 22.8°C, achieving a weight of 27.8 mg. Wolnicki and Myszkowski (1998) reported a weight of 40 mg reached by larvae at a density of 30 l−1 fed on Artemia nauplii in excess seven times for 13 hours a day during 20 days at 23°C, and Fleig et al. (2001) supplied nauplii continuously for 14 h a day during 26 days at 26°C with a final growth of 24.7 mg. In a 20-day trial performed by Wolnicki et al. (2003), the weight achieved by larvae at a density of 45 l−1 fed on Artemia nauplii in excess six times for 12 h a day at 28°C was 31.7 mg. In the present study, larvae at a density of 100 l−1 reached 46.8 mg (15.5 mm) on the 25th day supplying Artemia nauplii in excess only once a day at 22.5°C, in spite of this temperature may be lower than the optimum for feeding and growth of this species. In our experimental facilities, we have observed repeatedly that freshly hatched Artemia nauplii are living and swimming for at least 12 h at 22°C in artesian well water. This fact was one of the bases for the present experimental design, considering that, while live food remains available for tench, it is not necessary to feed so frequently, and thus feeding labour can be reduced, at least at temperatures around 22°C. These considerations and the present results suggest that the assertion that the Artemia die after 30 and 60 min in freshwater (FAO 1996) should not be applied to nauplii stage.
In the laboratory, it seems possible to accelerate growth by extending the daily feeding period. For instance, Wolnicki et al. (2003) observed the fastest growth (17.6 mm and 88.8 mg) for larval tench stocked at 45 l−1 when nauplii were supplied manually in excess ten times throughout 24 h a day at 28°C and continuous artificial lighting during 20 days. In culture, with a view to commercial scale, all the related results must be evaluated in terms of labour, cost, space availability and application possibilities.
When feeding was restricted, the amount of 50 nauplii larva−1 day−1 was in excess only during the first 5 days of experiment and allowed high survival rates even at the highest density (360 larvae l−1), but the growth was low. So that, this amount of food may be sufficient at least for the first 25 days of exogenous feeding (at 22.5°C) if fast growth is not the priority. When feeding was in excess, this initial amount was increased progressively up to reach around 450 nauplii per larva and day at the end of the experiment. In these treatments, small amounts of dead nauplii were always observed in the tank bottoms, and also nauplii swimming during daylight hours. In fact, the greatest growth was with nauplii supply in excess, but the cost of Artemia cysts and the difficulties of maintaining high densities must be considered.
In this period of fish culture, different densities under controlled conditions are recommended according to the species: 50 larvae l−1 for the carp, Cyprinus carpio, (Billard 1995), 60 l−1 for the turbot, Scophthalmus maximus, (Menu and Person-Le Ruyet 1991), and 100 l−1 for the gilt-head seabream, Sparus aurata, the seabass, Dicentrarchus labrax, (Barnabé 1991) and the sole, Solea vulgaris, (Menu and Person-Le Ruyet 1991). In tench, larvae have been maintained at different densities under controlled conditions, but only Billard and Flajshans (1995) mention a specific experiment on density where mortality after 20 days at 16 larvae l−1 was higher than those recorded at 8 and 12 larvae l−1. In our experiments, greater densities were tested with good survival rates, and results show that a density of 100 l−1 is suitable for an acceptable growth during at least the first 25 days of exogenous feeding, supplying nauplii in excess once a day.
When food amount was restricted, there were not statistical differences from 20 up to 160 larvae l−1. Only when 320 larvae l−1 were stocked survival was significantly lower (77%), but final mean length did not show differences with the other densities. If the final number of larvae is considered, 246 animals l−1 were obtained for the highest density and only 19 l−1 for the lowest. In the same way, when feeding was in excess, at a density of 20 larvae l−1 the growth (44.9 mg) was much higher than the one recorded with 200 l−1 (28.6 mg), but the weight obtained per litre was around 0.8 and 5 g, respectively. Considering the relationship among the initial number of animals, final survival and growth and ration supplied, the new data reported here are useful to establish suitable stocking densities under both culture and experimental conditions.
To the Plan Nacional de I+D+i, Spain. Research Projects AGF97-0602 and ACU01-06.