RESULTS OF STOCKING EXPERIMENT WITH VIMBA BREAM (VIMBA VIMBA L.) REARED ON EITHER LIVE ZOOPLANKTON OR PREPARED FOOD

Robert Czerniawski, Józef Domagała, Tomasz Krepski, Łukasz Sługocki, Małgorzata Pilecka-Rapacz
Department of General Zoology, University of Szczecin, Szczecin, Poland

ABSTRACT

The effect of using live zooplankton in the hatchery for the survival and growth of hatchery-reared vimba bream in the wild was examined. A hypothesis that the fish fed on live zooplankton (LFG) during rearing would reach greater survival and faster growth rates in the wild than fodder-fed fish (PFG) was assumed. In the hatchery, from the first week of rearing the LFG achieved higher values of the length than the PFG. After the capture of the fish from the stream, the mean survival rate of the LGF (9.6%) was higher than those from the PFG (3.2%). The results of this study show that the live food given for hatchery-reared vimba bream affect their higher survival rate in the wild.

Key words: foraging skills, cyprinids, larvae rearing, fish restitution.

INTRODUCTION

Pollution, regulation of river beds and river dams in Europe led to adverse changes causing the disappearance of some anadromous and riverine fish species, e.g. sturgeon, Atlantic salmon, trout, vimba bream, grayling or nase carp [1, 9, 11, 21, 24]. Recently, the main way of restoration of the valuable river species of ichthyofauna is artificial reproduction and the rearing of larvae and fry prior to stocking in the wild [2, 4, 5, 6, 7, 8]. One of these species that requires artificial rearing prior to stocking is the vimba bream (Vimba vimba) [9, 22]. Despite the stocking of the rivers of Central Europe with hatchery-reared larvae and fry of vimba bream, in the last years the abundance of this species is still low [9, 13, 14, 20, 24]. Hence, it is necessary to search for a new way that will increase the survival and the abundance of vimba bream in the wild.

It is generally known that the larvae of cyprinids, at the beginning of an exogenous diet, mainly eat the smallest plankton such as the crustaceans nauplii and rotifers. Therefore, in their rearing, the nauplii of Artemia salina are very often used [4, 10, 11]. These nauplii are a rich source of protein and vitamins [10]. However, after a relatively short time of rearing on brine shrimp nauplii, the larvae are reared on prepared food [11]. From an economic and commercial point of view this is clear and understandable, because the new fodder offers more proteins and vitamins than the nauplii of Artemia. However, the artificially prepared food given to larvae as stock does not develop the foraging skills needed for the capture of live food in the wild. The stocking experiments with the use of the live zooplankton and their influence on the survival and growth of hatchery-reared salmonids completed a success [4, 5]. Supplementation with live food or a supplement of natural elements in rearing can positively affect the survival of fish released into the wild [2, 18, 26]. It is caused by shaping such foraging skills necessary to live in the wild. Hence, the use in rearing of vimba bream larva as the stock of live zooplankton could lead to better results of stocking. The longer time of rearing on fodder and the releasing of the older fish to the wild should improve the survival rates too, but the longer time of rearing raises the cost of the entire restoration project. Thus, we have to find such ways of rearing the larvae of vimba bream as stock that reduces the costs and improves the effectiveness of stocking.

The aim of this study was to determine the effect of using live zooplankton in the hatchery for the survival and growth of hatchery-reared vimba bream in the wild. We assumed a hypothesis that the fish fed on live zooplankton during rearing would reach greater survival and faster growth rates in the wild than fodder-fed fish.

MATERIALS AND METHODS

The hatchery-reared fry of the vimba bream (Vimba vimba) were used for the stocking experiment. The fish were from the hatchery of Polish Angling Association in Goleniów. The larvae were reared for seven weeks in six tanks (three replicates for each variant), and then released into the wild. The volume of water in the tanks was 55 L. The water temperature was kept between 14ºC (at the beginning of rearing) and 18ºC (at the end of rearing) by a cooling device. Every week the temperature in stream (designed for stocking) was checked and any changes in temperature were then changed in the hatchery. The density of fish in each tank was 500 fish. The rearing was performed in a closed recirculation system in two variants: the live-fed group (LFG) – larvae fed on live nauplii of Artemia salina and live rotifer Brachionus pictilatus, and the pellet-fed group (PFG) – larvae fed on prepared food (Skretting, Gemma Micro 300 pre starter, contents: 55% protein and 15% fat, pellet size 200–400 µm). Live food was received from the culture of zooplankton. The food for the LFG and PFG was given ad libitum on the waters’ surface.

After seven weeks of rearing, (27th June 2012), the fish were released into the upper section of the small stream Trawna. This stream is ca. 7 km long, with a mean width of 2 m, a mean depth of 0.15 m and ending in the Płonia River. The bottom is predominantly covered with sand. The water temperature in summer does not exceed 20ºC. The water discharge on stocking day was 0.24 m³·s^-1. On stocking day the water temperature was 18ºC. The fish were transported to the stocking place in plastic bags saturated with oxygen. The distance between the hatchery and the stocking place was 10 km and the transport lasted 0.5 hour. The mortality of fish while being transported was not observed.

Fish survival was checked on the 29th September 2012, when they were captured with the use of electric fish gear. On capture day the water temperature was 15ºC. The fish were caught along the whole length of the stream. The fish were caught by three people: two people were collecting the fish, while the third person walked 50 meters behind them to check if the stunned fish which were left were not carried down the river. No other predatory species were caught because any other predatory fish had been caught with the use of an electric fish gear prior to stocking the stream with the hatchery-reared vimba.

Before releasing into the wild, the fry from the LFG were marked using fluorescence immersion on the second day following the completion of hatching. This was done by immersion for 3 hours in an alizarin red pigment solution at a concentration of 100 ppm. This method is effective and safe for fish growth and survival [19,23]. All the fish were killed by an overdose of MS-222. The otoliths of each captured fish were observed using an UV-light microscope, in order to check to which feeding group the fish belonged to.

The condition factor (K) was calculated by K = 105×M×L^-3, where: M – mass; L – total length. The statistical significance of the differences in the rate of survival of reared fish was tested by the non parametric Kruskall-Wallis test. While the statistical significance of the differences in the total length, mass and condition factor of the reared and captured fish was tested by the ANOVA and Duncan post-hoc test (P < 0.05).

RESULTS

Between replicates of the same groups a significant differences in the survival, total length and mass were not observed (P > 0.05).After rearing, the LFG achieved a significantly higher mean survival (95%) than the PFG (83%) (P < 0.05) (Tab. 1). The dead fish had been observed during each week of rearing, but their highest number was observed in the first three weeks (70%). From the first week of rearing the LFG achieved higher values of the length than the PFG (Fig. 1). Almost in each week of rearing significant differences in values of this parameter between the LFG and PFG were observed (P < 0.05). Only in the first and last week of rearing were the differences insignificant (P > 0.05).

Table 1. Mean ± SD total length, mass and condition factor of hatchery-reared vimba bream fry (LFG and PFG) captured from the wild

	n	Total length [mm]	Mass [g]	Condition factor
LFG	144	27.39 ± 2.18	1.909 ± 0.516	0.92 ± 0.10
PFG	48	27.07 ± 2.36	1.858 ± 0.635	0.91 ± 0.11

Fig. 1. Weekly changes of total length of vimba bream larvae reared on live food –– LFG and pellet food – PFG

After the capture of the fish from the stream, the survival rate of the LGF (9.6%) was higher than those from the PFG (3.2%) (Tab. 1). So, the results of the survival rate in the wild could be affected by the way of rearing. In the wild the LFG obtained higher mean values of length, mass and condition factor than the PFG; however, these differences between them were not significant (P > 0.05).

DISCUSSION

In the hatchery
The larvae of most of the cyprinids need to be fed initially with a natural diet, before weaning to a starter; otherwise their growth and survival may not be satisfactory [11]. The live diet in cyprinid larval feeding is considerably better than any dry diets. In rearing, the use of the nauplii of Artemia had a positive impact on the growth of the juvenile vimba bream, their increase of mass was significantly higher than larvae that were fed with a dry commercial diet [25].  Kamler and Wolnicki [11] reported that for the vimba bream larvae the live diet is especially important. The use of the starter as the first food for this species is wrong because they growth is impaired.

Hamackova et al. [9] obtained similar results in vimba bream larvae rearing. The greatest total length, mass and specific growth ratio was reached by the larvae of the vimba bream fed over the whole period with brine shrimp nauplii. While the lowest values of average length, mass and SGR were found in larvae fed during the whole period of rearing with the starter feed, the group fed live brine shrimp nauplii also achieved the higher survival rate compared to larvae fed starter, but insignificantly [9].

According to Hamackova et al. [9], from a biological point of view it is more suitable to rear the larvae of the vimba bream using live food up until the time of the final stages of the larval period of development. However, these authors say, that from an economic-technical point of view it seems to be the most suitable to rear larvae exclusively on a dry diet, that is, immediately after exogenic food to be taken. Moreover, the dry diet does not affect foraging skills of the larvae that will be needed by them to live in the wild. Nevertheless, in any given stage of development, larvae are fully able to accept both dry prepared food and live food, to grow intensively and to survive well [9, 11, 25].

With regard to our and the above-mentioned authors’ results, it can be concluded that in the rearing of the vimba bream larvae even an expensive and modern dry diet is less efficient than live diet.

In the wild
According to Morrison [16], live zooplankton is readily accepted as food because its continuous motion stimulates the interest of the fish and provokes them to attack. It seems that in the present study the important factor shaping the foraging skills of the vimba bream larvae during rearing was the motion of live zooplankton. Hence, as show in the present study results, the live zooplankton used during rearing could have a positive impact on the survival rates of hatchery-reared fry of the vimba bream in the wild. However, the survival rates were not high both for of the groups; it seems that the survival rate of the LFG was significantly higher than for the PFG. Moreover, usually vimba bream prefers larger stream for spawning. This is perhaps reported to low survival rates and foraging resources due to relatively high mortality of experimental fish, it is possible that conditions were  not suitable in the selected section of the stream. The suitable conditions could be more favorable in the larger stream or river where natural spawning of vimba bream takes place.

It should be noted that the absence of predators in the stocked stream also had an impact on the results of hatchery-reared vimba bream survival. According to Kennedy and Strange [12], survival and growth of stocked fish may be limited by the presence of predatory fish. In the stream, there were no predators. The possibility of fish migrating to the Płonia River was excluded. First, 80% of the fish were caught in the section located close the stocking section and far from the mouth of the stream to the Płonia River, and secondly, the first fish was caught at a place located 2.5 km before the mouth of the stream to the river.

Unfortunately, there are no studies on the stocking effectiveness of streams stocked with the hatchery-reared fry of the vimba bream. Therefore, we are forced to compare our results with those of restocking with hatchery-reared salmonids fry. Similar high results of the survival of hatchery-reared salmonids in the wild were observed by Czerniawski et al. [3, 5]. The live zooplankton was used as the significant factor in shaping the foraging skills of these fish. The survival rates of hatchery-reared one-year old Atlantic salmon, brown trout and sea trout reared on live zooplankton were even over 50% higher than those reared on pellet diet [3, 5]. The general conclusion of the studies was that the live zooplankton and live chironomidae larvae-diet supplied in the rearing has a positive impact on hatchery-reared trout survival in the wild. These authors reported that the live food used during rearing had a positive effect on foraging skills, survival rates and the growth of sea trout parr in the wild. The pellet diet used in rearing had a worse impact on fish behaviour in the wild. The results of young salmonids survival, noted by the other authors, who, prior to stocking into the wild, reared these fish on pellet-fodder, are also similarly low [7, 8].

CONCLUSIONS

Ecosystem-centred restitution programmes include, among others, captive breeding and restocking, based on genetic analysis, in order to sustain genetic diversity of the species [17]. In Poland, the vimba bream were previously an important fishery subject; [17] however, recently the natural population of this species is disappearing [20]. The critical state of V. vimba is the consequence especially of river pollution, damming rivers and overfishing in the past [15]. It is well known that natural spawning of fish is the best way to obtain a good condition of clutch larvae and their high survival rates. Nevertheless, Lusk et al. [15] believe that small, geographically-limited stocks can guarantee species genetic diversity, and therefore effort should be aimed at preserving them. Thus, restocking programmes based on local, native fish as a broodstock offer greater chances of success than programmes based on non-native hatchery stocks. [20]. In regard to the above statements and results of the present study, it seems that the best way to obtain satisfactory results of restocking with the vimba fry could be their rearing on live diet prior stocking to the wild. Larvae fed with live zooplankton during rearing, had already shaped the foraging skills and effectiveness of prey capture that influenced their survival and growth in the wild. The results of this study show that the live food given during rearing can contributed to increasing the survival of the vimba bream fry in the wild.

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Accepted for print: 23.09.2014

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Robert Czerniawski
Department of General Zoology, University of Szczecin, Szczecin, Poland
Z. Felczaka 3C
71-412 Szczecin
Poland
phone: +48 91 444 16 24
email: czerniawski@univ.szczecin.pl

Józef Domagała
Department of General Zoology, University of Szczecin, Szczecin, Poland
Z. Felczaka 3C
71-412 Szczecin
Poland
phone: +48 91 444 16 24
email: jozef.domagala@univ.szczecin.pl

Tomasz Krepski
Department of General Zoology, University of Szczecin, Szczecin, Poland
Z. Felczaka 3C
71-412 Szczecin
Poland

Łukasz Sługocki
Department of General Zoology, University of Szczecin, Szczecin, Poland
Z. Felczaka 3C
71-412 Szczecin
Poland

Małgorzata Pilecka-Rapacz
Department of General Zoology, University of Szczecin, Szczecin, Poland
Z. Felczaka 3C
71-412 Szczecin
Poland
phone: +48 91 444 16 24

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