Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.
Volume 9
Issue 1
Available Online: http://www.ejpau.media.pl/volume9/issue1/art-25.html


Mirosław Szczepkowski, Bożena Szczepkowska
Inland Fisheries Institute in Olsztyn, Poland



The possibility of using sturgeon as a stock component during the rearing of pike (Esox lucius L.) fry in tanks was determined. The experiment was conducted in two stages. In the first, pike fry with a body weight of 0.1 g were reared in monoculture and polyculture with a sturgeon component comprising 40 and 80% of the pike biomass. In the second phase, pike fry weighing an average of 3 g were reared in monoculture and polyculture with a sturgeon component comprising 10 and 20% of the pike biomass. The introduction of the sturgeon improved feed utilization and lowered feed conversion ratios from 1.4 to 0.8 in the older pike group (statistically significant difference at P < 0.05). In experiment stage II, the pike fry reared in polyculture with sturgeon attained statistically significant (P < 0.05) higher body growth in comparison with the monoculture variant. Pike survival was the lowest in the monoculture at 72.1 and 91.4% in stages I and II of the experiment, respectively. With regard to the smaller fry, this was due primarily to cannibalism with such losses comprising over 50% of the total losses throughout rearing. Survival in the polycultures was as much as 12% higher. The authors believe that the possibility of rearing these two species together stems from their different behavior and feeding strategy. Another benefit was that the labor-intensive removal of feed not consumed by the pike fry was lowered which meant that there was minimal interference in the tank during rearing.

Key words: pike, polyculture, recirculating systems, sturgeon.


Rearing fish in aquaculture is based on two basic systems – single-species stocks (monoculture) and multiple-species stocks (polyculture) [15]. The first method is applied during intense rearing, for example, in salmonid cultivation as it permits obtaining material of similar quality. Rearing in polyculture is successful in pond facilities where the natural feed base (zooplankton, benthos, small fish of little value) plays an important role. The introduction of additional stocking components permits taking fuller advantage of the existing feed base [3,7].

Rearing fish in recirculating systems is conducted almost exclusively in monoculture. Although fish of similar requirements, especially for water temperature and other physical and chemical parameters, are reared in one system, they are not reared together in the same tanks. This is mostly due to the conception that rearing should be as unified as possible, i.e., only one type of material of as uniform a size as possible should be reared on one type of feed. It is assumed that the feed supplied will be consumed to the fullest. However, in the case of many species of predatory fish (mainly larval and juvenile stages), the rearing technique applied involves feeding in excess so as to teach the fish quickly to consume artificial feed and prevent the phenomenon of cannibalism common during this period [1,19]. An additional problem is the fact that predatory fish will take feed almost exclusively from the water column and refuse to eat feed that has fallen to the bottom. In effect, a portion of the feed delivered during rearing goes unconsumed, and it pollutes the bottom of the tank and the environment of the recirculating system and becomes a source of nourishment for harmful bacteria. This also incurs economic losses as valuable protein, the most expensive component of fish feed, is wasted [21]. Unconsumed feed must be removed from the bottoms of tanks, which increases the labor intensity of rearing. The side-effects of tank waste removal include stress and the limitation of feeding time since fish do not normally feed during such interferences. An alternative method for removing feed remains might be the introduction of fish which would consume it without causing a negative impact on the main stock. It is possible that sturgeon might be able to play such a role as they are practically exclusive bottom feeders and are not carnivorous. The aim of the experiment was to study whether or not it is possible to use an additional stocking component of sturgeon during pike fry rearing and to determine how it impacted the results.


The experiment was conducted in spring 2004 at the Dgał Experimental Hatchery in Pieczarki in a recirculating system equipped with tanks made of artificial material with a volume of 1000 dm3 ST 12-10 (from SDK Ostróda). The experiment was conducted in two stages. Pike hatchlings with an average weight of 113 ± 5 mg were used in the first. The stock in each tank numbered about 1,000 pike. Three rearing variants were applied: without additional sturgeon stock (group S) and the addition of 125 and 250 Siberian sturgeon (Acipenser baeri Brandt) fry with an average body weight of 0.38 ± 0.04 g, which accounted for 40 and 80% of the pike biomass, respectively (groups J40 and J80). Each variant was conducted in two replicates. In the second stage, pike fry weighing 3.1 ± 0.1 g was used, while the stock addition was comprised of Siberian sturgeon fry weighing 9.6 ± 0.9 g. Rearing was conducted in monoculture (group J0) and with the addition of sturgeon at 10% (J10) and 20% (J20) of the pike biomass. Each variant was conducted in three replicates. Each of the two stages of the experiment was 14 days long. The fish stock in each tank was counted by hand. Measurements of fish weight and length were taken in vivo at the beginning and end of the experiment after the fish had been anesthetized with Propiscin [5]; each time, twenty specimens each of pike and sturgeon fry were taken from each tank. Mortality was noted daily in each tank, and all the fish were counted at the experiment’s conclusion. These figures were used to calculate survivorship and losses caused by cannibalism.

During the rearing period, the fish were fed with automatic band feeders for 21 hours per day beginning at 19:00. Nutreco commercial salmonid feed was used; Nutra Amino Balance 3.0 and 2.0 was used in experiment stage I, while Nutra Amino Balance 0 and Nutra T were used in experiment stage II. The ration size was calculated based on the pike biomass (the sturgeon was disregarded) using results from earlier experiments [10,12,13]. The feed conversion ratio (FCR) was calculated according to the formula:

FCR = F / B

F – amount of feed delivered (kg);
B – fish biomass increase (sturgeon and pike) (kg).

According to the preceding formula, the feed conversion ratio of rearing pike fry was also calculated in which biomass increase was only taken for pike fry growth. The specific growth rate (SGR) was also calculated according to the formula:

SGR = (ln Wk – ln Wp) D-1 100

Wk and Wp – initial (g) and final body weight;
D – number of rearing days (day).

The physical and chemical parameters of the water during the experiment are presented in Table 1. Measurements of oxygen content and pH were taken with a Cyber Scan 5500 (Eutech Instruments). Ammonia and nitrite contents were measured with the direct Nesslerization method using a Carl Zeiss 11 spectrophotometer for colorimetric measurement. Light intensity at the water surface was determined with a L-100 luxometer (Sonopan). The Statistica 5.0 Pl program was used for the statistical analyses of the data.

Table 1. Physical and chemical parameters during experimental rearing of pike (Esox lucius L.) fry with an additional sturgeon stock


First stage

Second stage

Average water temperature (°C)

20.7 ± 0.3

20.6 ± 0.3

Oxygen content (mg dm-3) – minimum




8.23 ÷ 8.47

7.88 ÷ 8.01

Water flow (dm3 min-1)



Light intensity (lx) – range

14.3 ÷ 34.0

92.8 ÷ 486.6

Ammonia concentration (NH3 + NH4+) – maximum



Nitrites (NO2-) – maximum




In the first stage of the experiment, the increase of pike fry body weight and length was similar (Table 2), and differences were not statistically different (P> 0.05). In the second stage of rearing, the highest body weight (6.70 g) was achieved by the older pike in group J20, and the difference with regard to the two other groups was statistically significant (P < 0.05). By the end of the experiment, the fish in this group had also achieved the longest body length (Table 3). In both stages of the experiment, the pike survival rates were the lowest in the monoculture at 72.1 and 91.4%, respectively (Tables 2 and 3). In the first stage, an important factor that contributed to fish losses was cannibalism. In the monoculture, losses due to this comprised 16.6% of the initial stock density and over 50% of all losses. Cannibalism was markedly lower in polyculture and losses caused by it were 8.9 and 4.5% of the initial stock for the J40 and J80 groups, respectively. In older fry, cannibalism did not play such an important role in any of the groups with maximum losses not exceeding 1.1% of the initial stock (group J20). The highest feed conversion ratios calculated for the whole stock, both pike and sturgeon, were obtained in the monoculture variants (groups S and J0) of both stages (Fig. 1 and 2). Differences between the values of feed conversion between groups J0 and J20 were statistically significant (P < 0.05). When only the increase in pike fry biomass is considered, the highest feed conversion values were also obtained in monoculture. The survival of sturgeon fry in the first stage of the experiment was 92.8 ± 2.3% in group J40 and 96.0 ± 2.8% in group J80, and in the second stage 90.0 ± 5.0% in group J10 and 96.7 ± 2.9% in group J20.

Table 2. Results of rearing pike (Esox lucius L.) fry in the first experimental stage


Experimental groups

without additional stock of sturgeons

additional stock of sturgeon 40% biomass of pike

additional stock of sturgeon 80% biomass of pike

Body weight (g)

1.33 ± 0.13

1.39 ± 0.25

1.27 ± 0.03

Body lenght (cm)

5.51 ± 0.09

5.53 ± 0.40

5.41 ± 0.04

Survival (%)

72.1 ± 7.4

84.0 ± 0.2

81.7 ± 5.0

Specific Growth Rate (% d-1)

17.76 ± 0.50

17.85 ± 1.31

17.30 ± 0.16

Condition Factor of Fulton

0.80 ± 0.02

0.81 ± 0.03

0.79 ± 0.00

Table 3. Results of rearing pike (Esox lucius L.) fry in the second experimental stage


Experimental groups

without additional stock of sturgeons

additional stock of sturgeon 10% biomass of pike

additional stock of sturgeon 20% biomass of pike

Body weight (g)

6.07 ± 0.64a

5.97 ± 0.44a

6.70 ± 0.60b

Body lenght (cm)

8.77 ± 0.28ab

8.66 ± 0.24a

8.97 ± 0.28b

Survival (%)

91.4 ± 1.2

95.0 ± 0.0

93.2 ± 6.2

SGR (% d-1)

4.82 ± 0.58

4.64 ± 0.79

5.32 ± 1.13

Condition Factor of Fulton

0.89 ± 0.01

0.91 ± 0.02

0.92 ± 0.01

Fig. 1. Feed conversion ratios during pike (Esox lucius L.) fry rearing in monoculture and polyculture with sturgeon in the first phase of the experiment

Fig. 2. Feed conversion ratios during pike (Esox lucius L.) fry rearing in monoculture and polyculture with sturgeon in the second stage of the experiment

There was considerable difference in the growth of pike and sturgeon fry in polyculture between the two stages of the experiment: in the first the growth of pike biomass exceeded that of sturgeon, while in the second, sturgeon growth was higher than that of pike. As a result, by the end of stage one of the experiment, sturgeon biomass had fallen in comparison to that of pike to 29.7% in group J40 and to 55.9% in group J80 (Fig. 3). The share of sturgeon had decreased by 26.3 and 27.4%, respectively, in groups J40 and J80. In the second stage of the experiment, the sturgeon biomass increased in comparison to that of pike and was 14.2% of the pike biomass in group J10 and 31.7% in group J20. In this instance, the weight share of sturgeon increased during the experiment by 45.9 and 45.6% in groups J10 and J20, respectively.

Fig. 3. Changes in the share of sturgeon fry biomass in relation to that of pike during rearing in polyculture


Fish from the family Acipenseridae are often used in pond polyculture, and advantageous results have been obtained when these species are used as an additional stock component in pond culture with herbivorous fish [8,9] or Wels catfish, Silurus glanis [16]. Studies conducted by the present authors have indicated that positive results can also be achieved in tank culture. The possibility of applying polyculture in this instance depends mostly on the differences in the behavior and feeding strategies of the species that are to be reared together. Throughout rearing, the pike fry occupied the upper water layer, while the sturgeon remained almost exclusively in the bottom zone. This meant that they did not compete directly for food. The pike fry consumed feed floating in the water column, while that which settled on the bottom was consumed by the sturgeon. The different behavior of these two species can also explain the differences in the level of cannibalism noted during the rearing of the smaller pike (experiment stage 1). In the monoculture, the authors observed that pike cannibals moved toward the bottom where they occupied a separate position. In polyculture, they did not assume this position as the presence of sturgeon agitated them thus limiting opportunities for them to attack other fish.

The second factor providing an impetus to seek possibilities of applying polyculture in systems of intense culture is the limitation of the negative impact of rearing on the water environment. Attempts to steer polyculture stocks appropriately have been made for many years. They are usually based on using species from different trophic levels, such as fish and algae or crustaceans [17], with algae most frequently used to remove nutrients from the water [2]. Substantially lower levels of ammonia nitrogen can be achieved in systems with this method [6]. Although the current study did not take into consideration the impact the addition of sturgeon had on water quality, feed utilization was substantially better, which meant that feed unconsumed by the pike did not have to be removed from the tanks. Obviously, the fact that the sturgeon consumed the feed on the bottom of the tank had a direct impact on the improvement of water quality. However, it should be borne in mind that the additional sturgeon stock can also negatively impact the environment of the closed system with its metabolic products and oxygen consumption [4,11,14]. Thus, further studies are required to determine the overall impact of the additional sturgeon stock on water quality.

In addition to the advantages listed above, the utilization of the sturgeon stock also meant that far less interference in the tank was necessary during rearing. In the current experiment, cleaning the tanks of unconsumed feed was necessary daily in the monoculture, while it was only required sporadically in polyculture. This is especially significant with regard to fish that are particularly sensitive to any kind of tank manipulation, as is the case with pike hatchling and fry [13].

Naturally, the simultaneous rearing of two species can also have its drawbacks, such as the necessity of sorting the species at the end of the rearing period. Currently, there is a lack of data necessary for the appropriate application of polyculture such as the optimal size of the additional stock or the size of the fish that can be reared together. The results of the current study seem to suggest that at least the biomass of the additional stock can vary within a relatively wide range. This was indicated by the fact that in both the first and second stages of the experiment, the ratio of the sturgeon to pike biomass share remained the same regardless of the initial addition of sturgeon. This indicates that, with the applied biotechnology of pike fry rearing, the pool of unconsumed feed is constant and, depending on the initial sturgeon biomass size, larger or smaller fry of this species is obtained.

The primary advantage of applying an additional stock was the improved consumption of high-protein feed. The results of stage I of the experiment indicated that the addition of sturgeon at almost 80% of the pike stock biomass permitted lowering the feed conversion ratio substantially in comparison to that in the monoculture even though the feed conversion ratios obtained during its rearing were similar to those from the rearing of other predatory fish, such as Wels catfish or zander (Sander lucioperca) [18,20]. Moreover, the economic effects of rearing are improved since, without the additional use of feed, a second valuable fish is produced. The third advantage of this method is the reduction in the labor required to clean the tanks and the indirect improvement of water quality. It appears that these bode well for the use of sturgeon in the rearing of pike fry, and possibly with other species in intensive tank rearing.


  1. The possibility of polyculture sturgeon and pike fry in tanks culture depends mostly on the differences in the behavior and feeding strategy of the species: the pike fry consume feed floating in the water column, while that unconsumed by the pike settled on the bottom of the tank and is consumed by the sturgeon.

  2. The introduction of the sturgeon as a stock component during the rearing of pike fry in tanks makes the possibilty of better feed utilization, lower feed conversion ratios and reduction in the labor required to clean the tanks.

  3. Cannibalism in pike fry was lower in polyculture and survival was as much as 12% higher than in monoculture.


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Mirosław Szczepkowski
Inland Fisheries Institute in Olsztyn, Poland
“Dgał” Experimental Hatchery in Pieczarki
Pieczarki 50, 11-610 Pozezdrze, Poland
phone: +48 87 428 36 66
email: szczepkowski@infish.com.pl

Bożena Szczepkowska
Inland Fisheries Institute in Olsztyn, Poland
“Dgał” Experimental Hatchery in Pieczarki
Pieczarki 50, 11-610 Pozezdrze, Poland
phone: +48 87 428 36 66

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