Acta Scientiarum. Biological Sciences ISSN: 1679-9283 [email protected] Universidade Estadual de Maringá Brasil

Figueiredo Lacerda, Carlos Henrique; Hayashi, Carmino; Martins Soares, Claudemir; Bento Fernandes, Carlos Eduardo Influence of aquatic plants on the predation of Piaractus mesopotamicus larvae by flavescens Acta Scientiarum. Biological Sciences, vol. 32, núm. 2, 2010, pp. 147-151 Universidade Estadual de Maringá .png, Brasil

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Influence of aquatic plants on the predation of Piaractus mesopotamicus larvae by

Carlos Henrique Figueiredo Lacerda1, Carmino Hayashi2, Claudemir Martins Soares3 and Carlos Eduardo Bento Fernandes3

1Laboratory of Ecology and Management of Estuarine and Coastal Ecosystems, Departamento de Oceanografia, Universidade Federal de Pernambuco, Cidade Universitária, Av. Arquitetura, s/n, 50740-550, Recife, Pernambuco, . 2Instituto de Pesca, Secretaria de Agricultura e Abastecimento do Estado de São Paulo, São Paulo, São Paulo, Brazil. 3Departamento de Biologia, Universidade Estadual de Maringá, Maringá, Paraná, Brazil. *Author for correspondence. E-mail: [email protected]

ABSTRACT. The experiment aimed to study the influence of the aquatic plants E. najas, P. stratiotes and S. auriculata on the predation of P. mesopotamicus larvae by P. flavescens. One hundred and twenty larvae of P. mesopotamicus and 24 larvae of P. flavescens were placed in 24 aquariums with capacity of 12 L, with one Odonate per aquarium. Treatments were different regarding the species of aquatic plants E. najas, S. auriculata and P. stratiotes, with one control treatment without aquatic plants. One aquarium (12 L) containing one Odonate and 30 P. mesopotamicus larvae was considered one experimental unit. After 18 hours, the Odonates were removed from the aquariums and fish larvae left (alive) were counted in each experimental unit. The survival rate of P. mesopotamicus larvae in the treatment without aquatic plants (control) was significantly lower than in the treatment with E. najas. However, the survival rates in the aquariums with floating aquatic plants did not differ from the control. The morphological characteristics of E. najas promoted higher structural complexity in the environment, offering more protection to the fish larvae, and increasing their survival. We concluded that the presence of the submerged aquatic plant E. najas promoted the reduction of predation of P. mesopotamicus larvae by Pantala flavescens. Key words: larvae, Piaractus mesopotamicus, Pantala flavescens, predation, aquatic plants.

RESUMO. Influência de macrófitas aquáticas na predação de de Piaractus mesopotamicus por Pantala flavescens. O experimento teve como objetivo estudar a influência de macrófitas aquáticas na predação de larvas de peixe P. mesopotamicus por larvas de P. flavescens Foram utilizadas 720 larvas de P. mesopotamicus e 24 larvas de P. flavescens, distribuídas em 24 aquários com volume útil para 12 L, sendo colocada uma de por aquário. Os tratamentos diferiram quanto à espécie de macrófita E. najas (E), S. auriculata (S) e P. stratiotes (P) sendo mantido um tratamento controle (C) sem macrófitas. Um aquário contendo uma larva de Odonata e 30 larvas de P. mesopotamicus foi considerado uma unidade experimental. Após 18 horas do início do experimento, as Odonatas foram retiradas dos aquários e foi realizada a contagem das larvas de peixe remanescentes (vivas) em cada unidade experimental. A taxa de sobrevivência das larvas de P. mesopotamicus no tratamento sem macrófita (controle) foi significativamente menor quando comparada ao tratamento contendo a macrófita submersa E. najas. Entretanto o valor de sobrevivência nos aquários com macrófitas flutuantes não diferiu do controle. As características morfológicas da E. najas promoveram uma maior complexidade estrutural no ambiente, gerando um maior numero de abrigos para as larvas de peixe, aumentando assim a sobrevivência das mesmas. Conclui-se que a presença da macrófita aquática E. najas promove redução na predação das larvas de P. mesopotamicus por larvas de P. flavescens. Palavras-chave: larvas, Piaractus mesopotamicus, Pantala flavescens, predação, macrófitas aquáticas.

Introduction aquatic macro- and microinvertebrates (LANSAC- TÔHA et al., 2003; TAKEDA et al., 2003), and Aquatic plants play an important role in the biomass, cover or diversity of aquatic plants. structure and functioning of aquatic ecosystems (THOMAZ et al., 2005). Recent studies in Brazilian Aquatic have been considered important reservoirs showed a positive relationship between predators of fish larvae in natural environments the diversity of fish species (AGOSTINHO et al., (McCORMICK; POLIS, 1982; LOUARN; 2003; PELICICE et al., 2005) and the richness of CLOAREC, 1997). Young Odonates have an Acta Scientiarum. Biological Sciences Maringá, v. 32, n. 2, p. 147-151, 2010 148 Lacerda et al. important role in the dynamics of aquatic Material and methods ecosystems and are considered one of the main The experiment was conducted at the predators of the littoral zone of lakes (SOTO; Aquaculture Laboratory of the Biology Department FERNÁNDES-BADILLO, 1994; LOUARN; at State University of Maringá (UEM), from CLOAREC, 1997; MARCO JR. et al., 1999), acting December 2005 to February 2006. as predators of other and fish larvae We used 720 larvae of pacu (P. mesopotamicus) (SOARES et al., 2001). obtained from regional fingerling producers by According to McGrinty (1980), Odonate larvae artificial fertilization, in the pre-flexion phase. of Pantala sp. were responsible for the consumption Twenty-four larvae of Odonate (P. flavescens) were of all catfish larvae (Ictalurus punctatus), when stored also used. To obtain the Odonate larvae, we used seven in tanks without chemical control. However, in fiberglass pools (six with 120 L volume and one with tanks with chemical treatment, the survival of a 1,000 L volume) installed outside for adults of Ictalurus punctatus larvae was around 85%. Odonate to lay eggs. The pools were washed, Few studies assessed the influence of Odonates supplied with water and fertilized with chemical in fish larvae survival, especially with Brazilian fertilizer (NPK-7:14:8), and were also inoculated species. Since predation and starvation are with plankton to promote the availability of food for considered the main agents of larval mortality, the developing larvae. Forty days after fertilization, predation can act as a determinant mechanism on Odonate larvae were collected with the help of a net the recruitment of many fish species (GERKING, with 1 x 1 mm mesh size and a hand net with a 1994; PARADIS et al., 1996). diameter of 25 cm and 1 mm mesh. The Odonates There are many variables that can influence the were selected according to size and separated into predation of fish larvae by predators. Turbidity, food homogeneous lots to be used in the experiment. availability, eyes and swimming capacity, nutritional We used 24 larvae of Odonates, measures of condition of larvae, water flow and growth rate of ocular lens, and selected individuals with sizes the larvae are among the factors considered between 12.83 and 14.33 mm. The size of Odonates important to ensure high survival rates used was based on the results found by Soares et al. (NORCROSS; BECK, 1984; NAKATANI et al., (2001) and their availability. Larvae were distributed 2005). The habitat complexity, often related to in 24 aquariums with 12 L water volume, one increasing diversity, may influence the survival of Odonate per aquarium. The experiment was some species of fish in the early stages of conducted in a randomized design with four development, during which many species use the treatments and six replications. The treatments coastal region as the main area of residence. differed in species of aquatic plants (E. najas, P. Van De Meutter et al. (2004) called attention to stratiotes and S. auriculata) and their presence or the areas occupied by aquatic plants where, absence. The aquariums were installed in two iron according to the authors, the density of Odonate shelves, supplied with water from an artesian well larvae and the total predation rates per unit area can and under constant lighting with fluorescent lamps be higher than in open water. Therefore, greater of 25 watts at 45 cm from the bottom of the understanding of the various biotic and abiotic aquarium. An aquarium containing one Odonate factors is necessary. and 30 fish larvae (P. mesopotamicus) was considered Fish larvae represent the most critical phase to an experimental unit. the success of the species, and are different from the The pH, electrical conductivity and dissolved oxygen were measured at the beginning and end of adults in regards to their ecological requirements. the experiment by means of Bernauer digital Thus, knowledge of this phase is essential to devices. A mercury thermometer was used to understanding self-ecology and population measure temperature. dynamics (NAKATANI et al., 2001), which can The Odonates were placed in aquariums one assist in the implementation of measures for hour before the pacu larvae; this moment was management and conservation of the fauna under considered the beginning of the experiment. After anthropological impacts. 18h, the Odonates were removed from the The objective of this study was to evaluate the aquariums and fish larvae remaining (alive) in each influence of aquatic plants Egeria najas, Pistia stratiotes sampling unit were counted. As control, we used and Salvinia auriculata on the predation of Piaractus four aquariums, each representing a treatment, but mesopotamicus larvae by Pantala flavescens. without the presence of Odonates. Acta Scientiarum. Biological Sciences Maringá, v. 32, n. 2, p. 147-151, 2010 Aquatic plants on fish larvae predation by Odonate 149

The aquatic plants used in the experiments were submerged, submerged species grow fully into obtained from the floodplain of Parana river and water, often occupying the entire water column and kept in water tanks, with a volume of 1000 L, in the thus may have more structural complexity in the Laboratory. To be used in treatments, the aquatic environment they are found. plants was selected by size, washed in running water The lower survival rate of P. mesopotamicus larvae and weighed, to ensure each replication produced in the absence of aquatic plants (control), when similar biomass of aquatic plants species. In each compared to the values found with the presence of experimental unit, the area occupied by aquatic E. najas, is probably related to the fact that this plants for each treatment was approximately 50% of species occupy the water column and provides more the aquarium, and was defined by visual criterion. shelters for the fish larvae, hindering the The analyzed variable was the number of prey visualization of P. mesopotamicus larvae by Odonates, consumed. reducing the frequency of occurrence of encounters Data of fish larvae consumption by larvae of between predator and prey. Odonates and the physical and chemical parameters According to Boyd (1971) and Barko et al. of water were tested by statistical analysis using (1986), aquatic plants act as important components Multivariate analysis of variance (MANOVA) and of lakes, rivers and other water bodies, providing analysis of variance (ANOVA) by protected shelter for spawning and protection of young stages ANOVA protocol. In cases of statistical difference, of aquatic organisms. Van De Meutter et al. (2004) the Tukey test was used at 5% probability. remember that the density of Odonate larvae can be greater in environments with aquatic plants, making Results and discussion the total predation rates per unit area larger than in open water. In this study, under experimental The average values of physical and chemical conditions, with the same space and density of prey variables of water showed no statistical difference and predators, the presence of aquatic plants had a (p > 0.05) between them, and remained in an positive impact on the survival of prey. appropriate range for the development and Pacu larvae consumed by Odonates in the metabolism of organisms used in this experiment control treatment (mean = 16.4 ind) was higher (EGNA; BOYD, 1997) (Table 1). than that found by Soares et al. (2001) studying the Table 1. Mean values of physical and chemical variables of water predation of Simocephalus serrulatus larvae by Pantala in the aquariums with different aquatic plants and control. sp., even with the use of a density five times higher,

Treatment Dissolved Electrical pH Temperature but with two predators per experimental unit. Oxygen condutivity (oC) According to Houde (2002), predation is the main -1 -1 (g L ) (μS mS ) factor controlling the population growth rate of beginning 5.44 0.15 7.24 24.00 Control end 5.14 0.14 7.32 23.75 most species of fish that have high fertility. This beginning 5.36 0.15 7.23 24.00 E. najas author argues further that even small changes in end 4.02 0.14 7.29 23.75 beginning 4.18 0.14 7.25 24.00 mortality in the larval stage can cause changes of S. auriculata end 4.15 0.14 7.28 24.00 great magnitude in the recruitment of populations. beginning 4.16 0.14 7.24 24.00 P. stratiotes end 3.83 0.15 7.21 24.00 Thus, according to data obtained in the experiment, aquatic environments with the presence of E. najas can influence positively the survival of fish larvae, The survival rate of P. mesopotamicus larvae in the reducing predation by Odonate larvae and control treatment (without aquatic plants) was encouraging the recruitment of the fish species. significantly lower (p < 0.05), compared to the Although P. mesopotamicus larvae of treatments treatment containing the submerged species E. najas with E. najas and P. stratiotes had survival values 15.8 (Figure 1). However, the value of survival in and 8.0% respectively (Figure 1), higher than those aquariums with floating species (P. stratiotes and S. found in the control treatment, no statistically auriculata) did not differ (p > 0.05) from the control. significant difference (p > 0.05) between the results No significant differences (p > 0.05) were observed was found. A possible explanation for the lack of between the values of survival in the treatments with significantly different results between the treatments submersed and floating species. is the high variance found in the data, which must Being submerged, E. najas has differentiated be related to the biology of the Odonate larvae, with morphology in relation to other species (S. auriculata changes in food consumption during development, and P. stratiotes), classified as floating. While the as reported by Soares et al. (2001). Thus, individuals floating species present only the root system with the same size can have a wide variation in Acta Scientiarum. Biological Sciences Maringá, v. 32, n. 2, p. 147-151, 2010 150 Lacerda et al. consumption rates by the proximity of the exchange Ecologia e manejo de macrófitas aquáticas. Maringá: of the exoskeleton (molt). Eduem, 2003. cap. 13, p. 261-279. BARKO, J. W.; ADAMS, M. S.; CLLESCERI, N. L. 68 Environmental factors and their consideration in the 66 Me an Mean Mean Mean Mean Mean+ stand + +standard standard ard error error error management of submersed aquatic vegetation. Journal of 64 F =F 2,9209= 2,9209 F = 2,9209p =p 0,0605= 0,0605 62 p = 0,0605 Aquatic Plant Management, v. 24, n. 1, p. 1-10, 1986. 60

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