Journal of Fish Biology (2014) 85, 509–515 doi:10.1111/jfb.12427, available online at wileyonlinelibrary.com
Planktonic or non-planktonic food in young-of-the-year European perch Perca fluviatilis in ponds M. Bláha*†, I. Šetlíková‡, J. Peterka§, J. Musil‖ and T. Policar* *Faculty of Fishery and Protection of Waters, South Bohemian Research Centre of ˇ Aquaculture and Biodiversity of Hydrocenoses, University of South Bohemia in Ceské Budˇejovice, Zátiší 728/II, 389 25 Vodˇnany, Czech Republic, ‡Faculty of Agriculture, ˇ ˇ University of South Bohemia in Ceské Budˇejovice, Studentská 13, 370 05 Ceské Budˇejovice, Czech Republic, §Biology Centre of the AS CR, v.v.i., Institute of Hydrobiology, Na Sádkách ˇ 7, 370 05 Ceské Budˇejovice, Czech Republic and ‖T. G. Masaryk Water Research Institute, Department of Aquatic Ecology, Podbabská 2582/30, 160 00 Prague, Czech Republic (Received 25 January 2014, Accepted 9 April 2014) Higher biomass especially of some aquatic macrophyte species offered a higher density of phytophilous zoobenthos, but did not increase the proportion of non-planktonic to planktonic prey in young-of-the-year perch Perca fluviatilis. Both abundance and biomass of non-planktonic prey dominated over planktonic prey in the pond with lower biomass of aquatic macrophytes and lower food. Survival of P. fluviatilis was lower (20%) in the pond with lower food than in the other pond (34%), however, specific growth rate (1⋅3% day−1 ) and final Fulton’s condition factor of P. fluviatilis were similar in both ponds. © 2014 The Fisheries Society of the British Isles
Key words: aquatic macrophytes; phytophilous zoobenthos; sediment zoobenthos; semi-intensive fish culture; zooplankton.
Young-of-the-year (YOY) perch Perca fluviatilis L. 1758 are planktivorous (Treasurer, 1990; Mehner et al., 1995) and switch from zooplankton to zoobenthos feeding at a total length (LT ) of 14–18 mm and at an age of 30–40 days (Guma’a, 1978; Berezina & Strel’nikova, 2001). Adámek et al. (2004), Okun & Mehner (2005) and Heynen et al. (2010) reported that YOY P. fluviatilis feed in littoral belts of aquatic macrophytes or in shallow water reservoirs, but they did not quantify aquatic macrophyte biomass and the phytophilous fauna used by P. fluviatilis. Both abundance and biomass of zoobenthos are much higher in communities of aquatic macrophytes than in open-water vegetation-free zones (Hargeby et al., 1994). Phytophilous (epiphytic) fauna in the diet of YOY P. fluviatilis was studied on Potamogeton pectinatus in the tail-water of a river (Dukowska et al., 2012), and by Boll et al. (2012) in artificial plant beds in a shallow lake. There has been no evaluation, however, of †Author to whom correspondence should be addressed. Tel.: +420 387 774 611; email: [email protected]
509 © 2014 The Fisheries Society of the British Isles
510
M . B LÁ H A E T A L.
feeding on non-planktonic food originating from the littoral (mostly emergent) aquatic macrophytes by YOY P. fluviatilis in fishponds. It could be assumed that the intake of this food will increase with increasing aquatic macrophyte biomass, but Diehl (1988) and Diehl & Eklöev (1995) reported that YOY and 1+ year P. fluviatilis fed less in a complex habitat with high macrophyte abundance than they did in open water. The aim of this study was to evaluate the growth and diet of YOY P. fluviatilis from April to September 2005, in relation to the origin of particular prey items in two ponds (South Bohemia, Nové Hrady) with different littoral macrophyte cover. Both planktonic and non-planktonic foods were included. The areas of the ponds were 0⋅88 and 0⋅39 ha and mean water depths at the outlet were 1⋅5 and 1⋅7 m in the LM pond (low macrophyte cover) and in the HM pond (high macrophyte cover), respectively. At the end of April, ponds were stocked with free swimming P. fluviatilis larvae (median LT = 7 mm; 120 000 individuals ha−1 ), and the ponds were harvested on 30 September 2005. The respective mean water temperatures (measured at 2 h intervals) were 16⋅5∘ C (minimum and maximum: 6 and 23∘ C) and 17⋅5∘ C (5 and 25∘ C) in LM and HM, respectively, during the experiment. The temperature sum (defined as the cumulative sum of daily mean temperature during the experiment) was 2602∘ C (i.e. 16⋅7 degree days) and 2687∘ C (i.e. 17⋅2 degree days) in LM and HM, respectively. Other abiotic factors are given in the study of Bláha et al. (2013). Monthly sampling of P. fluviatilis (on average 103 and at least 20 individuals for diet analysis at each sampling date), zooplankton, sediment zoobenthos, phytophilous zoobenthos and aquatic macrophytes were conducted according to standardized methods reported in the study of Bláha et al. (2013). Rotifera, Hydracarina, Copepoda and planktonic Cladocera (excluding benthic Cladocera: Acroperus, Alona and Chydorus) in the gut were considered as planktonic prey. Fishes were treated separately from other non-planktonic prey. Specific growth rate of P. fluviatilis was estimated as SGR = 100 (ln LT1 − ln LT0 ) t−1 , where LT1 and LT0 represent means of P. fluviatilis LT0 at the beginning of the survey (28 April) and LT1 at the end of survey (30 September), and t is the duration of the study. Fulton’s condition factor (K) was calculated as K = 100 M B LT −3 , where M B is body mass in g and LT is in mm. Normality was tested using the Kolmogorov–Smirnov test (Zar, 1984) in the Statistica for Windows (9.1) programme (www.statsoft.com). Box–Cox transformation was used to normalize the data. Either a t-test or the non-parametric Mann–Whitney rank sum test was used for comparison of the ponds. Significance level was set at P < 0⋅05. Normalized data (density of zooplankton, sediment zoobenthos and phytophilous zoobenthos) and other data are presented as mean ± s.d. and median with the lower and upper quartiles. Water temperature differed significantly between the ponds and was lower in LM than in HM (Mann–Whitney U = 152 716, P < 0⋅001). The vegetated area represented 14 and 33% of the total area of LM and HM ponds, respectively. Mean dry biomass of aquatic macrophytes was significantly lower in LM (208 ± 103 g m−2 of vegetated area) than in HM (399 ± 217 g m−2 of vegetated area) (t-test, t16 = 2⋅4, P < 0⋅05). Not only the density of aquatic macrophytes, but also the biomass m−2 of the total pond area were significantly lower in LM (29 ± 14 g m−2 ) than in HM (132 ± 72 g m−2 ) (t-test, t16 = 4⋅2, P < 0⋅01). Typha latifolia, Sparganium emersum, Warnstorfia fluitans, Glyceria fluitans and Carex sp. had highest mean biomasses in LM. Glyceria fluitans, Eleocharis acicularis, Alisma plantago-aquatica, T. latifolia and Alopecurus aequalis
© 2014 The Fisheries Society of the British Isles, Journal of Fish Biology 2014, 85, 509–515
T Y P E S O F F O O D I N YOY P E R C A F L U V I AT I L I S
511
(ordered according to mean biomass) were the dominant aquatic macrophyte species in HM. Zooplankton, and both sediment and phytophilous zoobenthos densities did not differ significantly between ponds (t-test, t16 = 1⋅1, t16 = 0⋅3, t16 = 1⋅7, respectively, P > 0⋅05). This may be because of the large variation in density of the communities, as the abundances of all prey types were lower in LM than in HM. Mean density of zooplankton in LM (193 ± 146 individuals l−1 ) was c. half of that in HM. Furthermore, LM exhibited only one third of the mean density of the sediment zoobenthos in HM (658 ± 885 individuals m−2 ). In spite of the different densities of aquatic macrophytes, mean total density of phytophilous zoobenthos m−2 of vegetated areas did not differ significantly between ponds (t-test, t16 = 1⋅7, P > 0⋅05). The reason may be that chironomid larvae massively colonized (13 individuals g−1 ) the inner area of S. emersum leaves in LM. Specific mass of S. emersum was lower than that of other aquatic macrophytes present due to its aerenchymatous tissue. As a result, this species offered more habitat space g−1 dry mass than the other macrophytes present. Nevertheless, phytophilous zoobenthos in HM was about three times more numerous than in LM (214 v. 67 individuals m−2 of total pond area). Perca fluviatilis originating from LM fed on significantly (Mann–Whitney U = 9002, P < 0⋅001) fewer individuals [28 individuals fish−1 (5–78 individuals fish−1 )] than from HM [90 individuals fish−1 (17–195 individuals fish−1 )] throughout the experiment. Perca fluviatilis (7 mm LT ) fed exclusively on zooplankton, especially nauplii and copepodids of cyclopoid copepods during the first 13 days after stocking. Abundance of prey items did not differ significantly (Mann–Whitney U = 631, P > 0⋅05) between LM [0 individuals fish−1 (0–3 individuals fish−1 )] and HM ponds [1 individual fish−1 (0–5 individuals fish−1 )] in this period. On 10 May, most P. fluviatilis in LM (11 mm LT ) preferred Polyarthra sp. and nauplii. At this time, P. fluviatilis (13 mm LT ) fed on Eudiaptomus gracilis, Cyclops strenuus and Daphnia pulicaria in HM. Perca fluviatilis began to feed on non-planktonic prey from early June (34 mm LT ), i.e. 41 days after stocking (7 June). Non-planktonic prey was represented by Hirudinea, Aranea, Ostracoda, Isopoda, Collembola and Insecta (Ephemeroptera, Odonata, Plecoptera, Hemiptera, Megaloptera, Trichoptera, Diptera and Coleoptera). Mean number of prey consumed by each P. fluviatilis was significantly lower in LM than in HM [53 individuals fish−1 (20–104 individuals fish−1 ) in LM and 119 individuals fish−1 (58–284 individuals fish−1 ) in HM] (Mann–Whitney U = 4018, P < 0⋅001). Nevertheless, the mean share of non-planktonic prey abundance [83% (63–96%) and biomass 48 mg fish−1 (27–92 mg fish−1 )] was significantly higher in LM than in HM [56% (13–87%) and 37 mg fish−1 (19–66 mg fish−1 )] (both Mann–Whitney U = 4855 and 11 619, both P < 0⋅001). Contrary to expectations, mean abundance of non-planktonic prey [19 individuals fish−1 (0–54 individuals fish−1 )] was significantly higher than the abundance of planktonic prey [3 individuals fish−1 (0–54 individuals fish−1 )] in LM (Mann–Whitney U = 11 035, P < 0⋅01). These abundances [planktonic: 18 individuals fish−1 (2–110 individuals fish−1 ) and non-planktonic: 24 individuals fish−1 (1–64 individuals fish−1 )] did not differ significantly (Mann–Whitney U = 10 866, P > 0⋅05) in HM. In both ponds, abundance of non-planktonic prey dominated over planktonic prey in the middle of the growing season (29 June to 25 July). This prevalence persisted until 24 August in LM (Fig. 1). In the mesocosm experiment by Berezina & Strel’nikova (2001), non-planktonic prey (larvae of chironomids and other insects) comprised
© 2014 The Fisheries Society of the British Isles, Journal of Fish Biology 2014, 85, 509–515
512
M . B LÁ H A E T A L.
Prey abundance (%)
(a)
(b)
100 80 60 40 20
12 September
24 August
25 July
29 June
7 Junuary
12 September
24 August
25 July
29 June
7 Junuary
0
Date
Fig. 1. Abundance of planktonic ( ) and non-planktonic prey ( ) in Perca fluviatilis diet in (a) low macrophyte cover (LM) and (b) high macrophyte cover (HM) ponds from the time of the first appearance of non-planktonic prey.
maximally half of the total prey abundance in YOY P. fluviatilis (33 mm LT ). The relative content of non-planktonic food would be higher (as in the present experiment), however, if benthic Cladocera are considered separately from planktonic prey. Furthermore, as reported in other studies (Guma’a, 1978; Persson & Greenberg, 1990; Okun et al., 2005) low abundance of zooplankton (
Planktonic or non-planktonic food in young-of-the-year European perch Perca fluviatilis in ponds M. Bláha*†, I. Šetlíková‡, J. Peterka§, J. Musil‖ and T. Policar* *Faculty of Fishery and Protection of Waters, South Bohemian Research Centre of ˇ Aquaculture and Biodiversity of Hydrocenoses, University of South Bohemia in Ceské Budˇejovice, Zátiší 728/II, 389 25 Vodˇnany, Czech Republic, ‡Faculty of Agriculture, ˇ ˇ University of South Bohemia in Ceské Budˇejovice, Studentská 13, 370 05 Ceské Budˇejovice, Czech Republic, §Biology Centre of the AS CR, v.v.i., Institute of Hydrobiology, Na Sádkách ˇ 7, 370 05 Ceské Budˇejovice, Czech Republic and ‖T. G. Masaryk Water Research Institute, Department of Aquatic Ecology, Podbabská 2582/30, 160 00 Prague, Czech Republic (Received 25 January 2014, Accepted 9 April 2014) Higher biomass especially of some aquatic macrophyte species offered a higher density of phytophilous zoobenthos, but did not increase the proportion of non-planktonic to planktonic prey in young-of-the-year perch Perca fluviatilis. Both abundance and biomass of non-planktonic prey dominated over planktonic prey in the pond with lower biomass of aquatic macrophytes and lower food. Survival of P. fluviatilis was lower (20%) in the pond with lower food than in the other pond (34%), however, specific growth rate (1⋅3% day−1 ) and final Fulton’s condition factor of P. fluviatilis were similar in both ponds. © 2014 The Fisheries Society of the British Isles
Key words: aquatic macrophytes; phytophilous zoobenthos; sediment zoobenthos; semi-intensive fish culture; zooplankton.
Young-of-the-year (YOY) perch Perca fluviatilis L. 1758 are planktivorous (Treasurer, 1990; Mehner et al., 1995) and switch from zooplankton to zoobenthos feeding at a total length (LT ) of 14–18 mm and at an age of 30–40 days (Guma’a, 1978; Berezina & Strel’nikova, 2001). Adámek et al. (2004), Okun & Mehner (2005) and Heynen et al. (2010) reported that YOY P. fluviatilis feed in littoral belts of aquatic macrophytes or in shallow water reservoirs, but they did not quantify aquatic macrophyte biomass and the phytophilous fauna used by P. fluviatilis. Both abundance and biomass of zoobenthos are much higher in communities of aquatic macrophytes than in open-water vegetation-free zones (Hargeby et al., 1994). Phytophilous (epiphytic) fauna in the diet of YOY P. fluviatilis was studied on Potamogeton pectinatus in the tail-water of a river (Dukowska et al., 2012), and by Boll et al. (2012) in artificial plant beds in a shallow lake. There has been no evaluation, however, of †Author to whom correspondence should be addressed. Tel.: +420 387 774 611; email: [email protected]
509 © 2014 The Fisheries Society of the British Isles
510
M . B LÁ H A E T A L.
feeding on non-planktonic food originating from the littoral (mostly emergent) aquatic macrophytes by YOY P. fluviatilis in fishponds. It could be assumed that the intake of this food will increase with increasing aquatic macrophyte biomass, but Diehl (1988) and Diehl & Eklöev (1995) reported that YOY and 1+ year P. fluviatilis fed less in a complex habitat with high macrophyte abundance than they did in open water. The aim of this study was to evaluate the growth and diet of YOY P. fluviatilis from April to September 2005, in relation to the origin of particular prey items in two ponds (South Bohemia, Nové Hrady) with different littoral macrophyte cover. Both planktonic and non-planktonic foods were included. The areas of the ponds were 0⋅88 and 0⋅39 ha and mean water depths at the outlet were 1⋅5 and 1⋅7 m in the LM pond (low macrophyte cover) and in the HM pond (high macrophyte cover), respectively. At the end of April, ponds were stocked with free swimming P. fluviatilis larvae (median LT = 7 mm; 120 000 individuals ha−1 ), and the ponds were harvested on 30 September 2005. The respective mean water temperatures (measured at 2 h intervals) were 16⋅5∘ C (minimum and maximum: 6 and 23∘ C) and 17⋅5∘ C (5 and 25∘ C) in LM and HM, respectively, during the experiment. The temperature sum (defined as the cumulative sum of daily mean temperature during the experiment) was 2602∘ C (i.e. 16⋅7 degree days) and 2687∘ C (i.e. 17⋅2 degree days) in LM and HM, respectively. Other abiotic factors are given in the study of Bláha et al. (2013). Monthly sampling of P. fluviatilis (on average 103 and at least 20 individuals for diet analysis at each sampling date), zooplankton, sediment zoobenthos, phytophilous zoobenthos and aquatic macrophytes were conducted according to standardized methods reported in the study of Bláha et al. (2013). Rotifera, Hydracarina, Copepoda and planktonic Cladocera (excluding benthic Cladocera: Acroperus, Alona and Chydorus) in the gut were considered as planktonic prey. Fishes were treated separately from other non-planktonic prey. Specific growth rate of P. fluviatilis was estimated as SGR = 100 (ln LT1 − ln LT0 ) t−1 , where LT1 and LT0 represent means of P. fluviatilis LT0 at the beginning of the survey (28 April) and LT1 at the end of survey (30 September), and t is the duration of the study. Fulton’s condition factor (K) was calculated as K = 100 M B LT −3 , where M B is body mass in g and LT is in mm. Normality was tested using the Kolmogorov–Smirnov test (Zar, 1984) in the Statistica for Windows (9.1) programme (www.statsoft.com). Box–Cox transformation was used to normalize the data. Either a t-test or the non-parametric Mann–Whitney rank sum test was used for comparison of the ponds. Significance level was set at P < 0⋅05. Normalized data (density of zooplankton, sediment zoobenthos and phytophilous zoobenthos) and other data are presented as mean ± s.d. and median with the lower and upper quartiles. Water temperature differed significantly between the ponds and was lower in LM than in HM (Mann–Whitney U = 152 716, P < 0⋅001). The vegetated area represented 14 and 33% of the total area of LM and HM ponds, respectively. Mean dry biomass of aquatic macrophytes was significantly lower in LM (208 ± 103 g m−2 of vegetated area) than in HM (399 ± 217 g m−2 of vegetated area) (t-test, t16 = 2⋅4, P < 0⋅05). Not only the density of aquatic macrophytes, but also the biomass m−2 of the total pond area were significantly lower in LM (29 ± 14 g m−2 ) than in HM (132 ± 72 g m−2 ) (t-test, t16 = 4⋅2, P < 0⋅01). Typha latifolia, Sparganium emersum, Warnstorfia fluitans, Glyceria fluitans and Carex sp. had highest mean biomasses in LM. Glyceria fluitans, Eleocharis acicularis, Alisma plantago-aquatica, T. latifolia and Alopecurus aequalis
© 2014 The Fisheries Society of the British Isles, Journal of Fish Biology 2014, 85, 509–515
T Y P E S O F F O O D I N YOY P E R C A F L U V I AT I L I S
511
(ordered according to mean biomass) were the dominant aquatic macrophyte species in HM. Zooplankton, and both sediment and phytophilous zoobenthos densities did not differ significantly between ponds (t-test, t16 = 1⋅1, t16 = 0⋅3, t16 = 1⋅7, respectively, P > 0⋅05). This may be because of the large variation in density of the communities, as the abundances of all prey types were lower in LM than in HM. Mean density of zooplankton in LM (193 ± 146 individuals l−1 ) was c. half of that in HM. Furthermore, LM exhibited only one third of the mean density of the sediment zoobenthos in HM (658 ± 885 individuals m−2 ). In spite of the different densities of aquatic macrophytes, mean total density of phytophilous zoobenthos m−2 of vegetated areas did not differ significantly between ponds (t-test, t16 = 1⋅7, P > 0⋅05). The reason may be that chironomid larvae massively colonized (13 individuals g−1 ) the inner area of S. emersum leaves in LM. Specific mass of S. emersum was lower than that of other aquatic macrophytes present due to its aerenchymatous tissue. As a result, this species offered more habitat space g−1 dry mass than the other macrophytes present. Nevertheless, phytophilous zoobenthos in HM was about three times more numerous than in LM (214 v. 67 individuals m−2 of total pond area). Perca fluviatilis originating from LM fed on significantly (Mann–Whitney U = 9002, P < 0⋅001) fewer individuals [28 individuals fish−1 (5–78 individuals fish−1 )] than from HM [90 individuals fish−1 (17–195 individuals fish−1 )] throughout the experiment. Perca fluviatilis (7 mm LT ) fed exclusively on zooplankton, especially nauplii and copepodids of cyclopoid copepods during the first 13 days after stocking. Abundance of prey items did not differ significantly (Mann–Whitney U = 631, P > 0⋅05) between LM [0 individuals fish−1 (0–3 individuals fish−1 )] and HM ponds [1 individual fish−1 (0–5 individuals fish−1 )] in this period. On 10 May, most P. fluviatilis in LM (11 mm LT ) preferred Polyarthra sp. and nauplii. At this time, P. fluviatilis (13 mm LT ) fed on Eudiaptomus gracilis, Cyclops strenuus and Daphnia pulicaria in HM. Perca fluviatilis began to feed on non-planktonic prey from early June (34 mm LT ), i.e. 41 days after stocking (7 June). Non-planktonic prey was represented by Hirudinea, Aranea, Ostracoda, Isopoda, Collembola and Insecta (Ephemeroptera, Odonata, Plecoptera, Hemiptera, Megaloptera, Trichoptera, Diptera and Coleoptera). Mean number of prey consumed by each P. fluviatilis was significantly lower in LM than in HM [53 individuals fish−1 (20–104 individuals fish−1 ) in LM and 119 individuals fish−1 (58–284 individuals fish−1 ) in HM] (Mann–Whitney U = 4018, P < 0⋅001). Nevertheless, the mean share of non-planktonic prey abundance [83% (63–96%) and biomass 48 mg fish−1 (27–92 mg fish−1 )] was significantly higher in LM than in HM [56% (13–87%) and 37 mg fish−1 (19–66 mg fish−1 )] (both Mann–Whitney U = 4855 and 11 619, both P < 0⋅001). Contrary to expectations, mean abundance of non-planktonic prey [19 individuals fish−1 (0–54 individuals fish−1 )] was significantly higher than the abundance of planktonic prey [3 individuals fish−1 (0–54 individuals fish−1 )] in LM (Mann–Whitney U = 11 035, P < 0⋅01). These abundances [planktonic: 18 individuals fish−1 (2–110 individuals fish−1 ) and non-planktonic: 24 individuals fish−1 (1–64 individuals fish−1 )] did not differ significantly (Mann–Whitney U = 10 866, P > 0⋅05) in HM. In both ponds, abundance of non-planktonic prey dominated over planktonic prey in the middle of the growing season (29 June to 25 July). This prevalence persisted until 24 August in LM (Fig. 1). In the mesocosm experiment by Berezina & Strel’nikova (2001), non-planktonic prey (larvae of chironomids and other insects) comprised
© 2014 The Fisheries Society of the British Isles, Journal of Fish Biology 2014, 85, 509–515
512
M . B LÁ H A E T A L.
Prey abundance (%)
(a)
(b)
100 80 60 40 20
12 September
24 August
25 July
29 June
7 Junuary
12 September
24 August
25 July
29 June
7 Junuary
0
Date
Fig. 1. Abundance of planktonic ( ) and non-planktonic prey ( ) in Perca fluviatilis diet in (a) low macrophyte cover (LM) and (b) high macrophyte cover (HM) ponds from the time of the first appearance of non-planktonic prey.
maximally half of the total prey abundance in YOY P. fluviatilis (33 mm LT ). The relative content of non-planktonic food would be higher (as in the present experiment), however, if benthic Cladocera are considered separately from planktonic prey. Furthermore, as reported in other studies (Guma’a, 1978; Persson & Greenberg, 1990; Okun et al., 2005) low abundance of zooplankton (
