Population structure and condition factor of Pseudotothyris obtusa (hypoptopomatinae) from three coastal streams in southern Brazil

Population structure and condition factor of Pseudotothyris obtusa (hypoptopomatinae) from three coastal streams in southern Brazil

Denise de Freitas Takeuti^I; José Roberto Verani^II; José Marcelo Rocha AranhaI, ^*; Márcia Santos de Menezes^I

^IDepartamento de Zoologia, Universidade Federal do Paraná, CP 19020, CEP 81531-990, Curitiba, Paraná, Brasil

^IIDepartamento de Hidrobiologia, Universidade Federal de São Carlos, CP 676, CEP 13565-905, São Carlos, São Paulo, Brasil

ABSTRACT

Population structure features and condition factor of Pseudotothyris obtusa were compared between three coastal streams in southern Brazil. Fishes were monthly collected through electric fishing and measured in the total length. Fifteen fishes from each stream were dissected to identify their sex. The structure in size, sex ratio and young/adults ratio of populations were analysed and the length-weight relationship was obtained. The condition factor (K₁) and the relative condition factor (K_n) were calculated for each stream. Fishes were grouped in 11 lenght classes of 3mm. The intermediate and bigger size classes were preponderant in the "Mergulhão" and "Colônia Pereira" streams, and the smaller and intermediate ones in the "Ribeirão" stream. Females prevailed in bigger size classes, reached bigger lengths than males, and were preponderant in all streams. The condition factors (K₁ and K_n) were different in all streams, indicating better condition and higher weight values in fishes from the "Mergulhão" and "Colônia Pereira" streams.

Key words: coastal streams, Pseudotothyris obtusa, Hypoptopomatinae, population structure, condition factor.

RESUMO

Características da estrutura da população e o fator de condição de Pseudotothyris obtusa foram comparados em três rios costeiros na região sul do Brasil. Os peixes foram coletados mensalmente através de pesca elétrica e medidos quanto ao comprimento total. Quinze peixes de cada rio foram dissecados e identificados quanto ao sexo. A estrutura da população em tamanho, a proporção sexual e a relação jovem/adultos foram analisadas e foi obtida a relação peso/comprimento. O fator de condição (K₁) e o fator de condição relativo (K_n) foram calculados em cada rio. Os peixes foram agrupados em 11 classes de comprimento de 3mm. As classes de tamanho maiores e intermediárias foram preponderantes nos rios Mergulhão e Colônia Pereira, e as classes menores e intermediárias no rio Ribeirão. Fêmeas prevaleceram nas maiores classes de comprimento, atingiram maiores comprimentos que os machos, e foram preponderantes em todos os rios. Os valores dos fatores de condição (K₁ and K_n) foram diferentes nos três rios, indicando melhor condição e maiores valores de peso total para os dos rios Mergulhão e Colônia Pereira.

INTRODUCTION

The bionomic strategies adopted by the species of fish can present tactical variations (Wootton, 1984), because fishes are capable of answering to the biotic and abiotic conditions in their environment. A certain degree of flexibility in the answers to the environment can be desirable in unstable places to make the survival of the species possible. In Brazil, variations in the life-history of fish species related to environment were found by many authors (Vazzoler, 1971; Garutti, 1989; Basile-Martins et al., 1986).

The population structure is an important aspect to be analysed in the biology of fish, because together with other aspects, they characterise the life strategy adopted by a species. The structure of a population can reflect the current and previous environmental conditions tried by the fish. On the same lines, the relationships between the structure of population and the structure of habitat were explored by Rakocinski (1988) with North American fish species. In Brazil, some authors studied the population structure of fish (e.g. Narahara et al., 1985; Basile-Martins et al., 1986) for the knowledge of the biology of a certain species.

The variations in the condition factor can indicate variations related to the fitness of the fish, development and fat accumulation (Le Cren, 1951). Then, it is possible that fish from different places, in different development phases and of different sexes present different values for these factors (Le Cren, 1951), indicating conditions peculiar to the place where the species inhabit.

There are many reports on the fish biology of the Loricariidae family (Agostinho et al., 1986; Menezes & Caramaschi, 1994). However, not much information is available Hypoptopomatinae.

This paper aims to characterise the structure in size, the sex ratio, the young/adult ratio, and to compare the condition factor of the populations of Pseudotothyris obtusa (Ribeiro, 1911), in three coastal streams of Paraná state: "Mergulhão", "Colônia Pereira" and "Ribeirão" streams.

MATERIAL AND METHODS

Samples of P. obtusa were monthly collected from March/1995 to March/1996, using electric fishing in an extension of approximately 50 m. For each sample, fifteen fishes were separated and measured for the total lenght (mm) and the total weight (mg). In laboratory, fishes were dissected, and their sex was identified.

Bimonthly samples were collected in order to obtain the large number of fishes, which were measured in terms of total length and returned to the stream.

Data referring to medium temperatures and precipitation were supplied by metereologic stations near the streams.

We adopted 11 classes of total length obtained from the Sturges formulation (Silva & Souza, 1987). In each stream the size class, the sex ratio and the young/adult ratio were analysed by the distribution of frequencies of the whole sample and the differences were tested by the χ ² test (α = 0.05). The length-weight relationship was initially obtained for males and females separately. The straight lines estimated for males and females were compared to each other by the interval of confidence of the straight line (95% of confidence) estimated for the whole data. This straight lines were obtained by the logarithmic transformations of the data.

According to this methodology, it was analysed if the straight line obtained for males and females separately were contained in the interval of confidence for the straight line obtained for both sexes together.

The condition factor (K1), excluding the weight of the gonads, and the relative condition factor (Kn) were calculated (Le Cren, 1951) for the females of each stream, and the test of Kruskal-Wallis was applied (Siegel, 1975) to verify differences. In case those differences were significant, the Dunn test of multiple comparison was applied, in order to verify in which streams the difference was significant.

STUDY SITES

The climate in the area is subtropical, without a dry season. The highest precipitation levels occurred from November/1995 to March/1996. The highest medium temperatures happened from March to April/1995 and from November/1995 to March/1996.

The "Mergulhão" stream (approximately 25º17'S; 48º44'W; Fig 1) is located in the municipality of Antonina and its head-waters are located at an altitude of 1,700m. The "Colônia Pereira" stream (approximately 25º41'S; 48º35'W; Fig 1) is located close to the municipality of Paranaguá and its head-waters are located at an altitude of 650m. The "Ribeirão" stream (approximately 25º36'S; 48º37'W; Fig 1) is 10 Km far from the "Colônia Pereira" stream. Its head-waters are located at an altitude of 766m.

A detailed characterisation of the sampled stretches is shown in the Table 1. In the three streams changes during periods of high precipitation occurred, such as the flash floods, which decreased the transparency of water, increased its speed, and cause the elevation of its level and the physical disturbance of the habitats.

RESULTS

In the studied streams P. obtusa was usually collected under litter, logs, branches and close to the vegetation in the palisades. We collected 1499 fishes (305 in "Mergulhão" stream, 549 in "Colônia Pereira" stream and 645 in "Ribeirão" stream) and adopted 11 classes of total length (Table 2).

In the three streams, the length amplitude varied from the class 12 to 14 mm to the class 42 to 44 mm (classes 1 to 11), except in the "Ribeirão" stream, where class 11 did not occur. We considered frequent classes those equal or superior to 20%. In the "Mergulhão" stream classes 8 and 9 were the most frequent; in the "Colônia Pereira" stream, classes 7, 8 and 9; and in the "Ribeirão" stream, class 5.

Males presented higher frequencies in the classes 7 and 8 in all the streams, whereas females presented higher frequencies in the classes 8 and 9 in the "Mergulhão" stream, in the classes 9 and 10 in the "Colônia Pereira" stream, and in the class 8 in the "Ribeirão" stream. The largest length reached by males was 39 mm in the "Mergulhão" stream (class 10), whereas in the "Colônia Pereira" and "Ribeirão" streams it was 35 mm (class 8). Females reached up to 43 mm of total length, except in the "Ribeirão" stream whose larger length was 40 mm.

The sex ratio was significantly different from 1:1, prevailing females in all streams, in the total samplies and in the majority of bimonthly ones (Figure 2).

Figure 3 presents the sex ratio for the length classes. It can be observed that there was prevalence of females in the largest size classes, in the three streams. In general, there was balance between sexes or males prevailed in classes from 1 to 4 and 7.

In the "Mergulhão" and "Colônia Pereira" streams, the young fishes were present in March-April and from September-October to March of 1996. In the "Ribeirão" stream the young were present during, all bimonthly periods. They were in larger proportion than adults from November-December to March of 1996.

The straight lines estimated for males and females separately were partially out of the interval of confidence of the straight line for all data. Therefore, they indicated differentiated relative growth for sexes. The expressions for males and females for the length-weight relationship were: males lnWt = -4.420 + 2.920 lnLt; and females lnWt = -5.355 + 3.204 lnLt.

We used the females relative growth constant (3.204) in the condition factor (K1) and the relative condition factor (Kn). Statistically significant differences between streams were found for the values of K1 (H=26.6; p <0.05) and Kn (H=29.1; p <0.05). The values of K1 were different in the three streams, being higher in the "Mergulhão" and "Colônia Pereira" streams and smaller in the "Ribeirão" stream (Table 3). The same was observed for the Kn values (Table 3).

DISCUSSION

P. obtusa was considered a frequent species in the sampling sites of the stream where the samples were collected, except in the "Mergulhão" stream, in which the species, in spite of frequent, was in smaller number (305 fishes captured in 13 samplings). Branches and under water roots made it very difficult the access to the left edge in this stream, and it could explain the smallest number of sampled fishes.

An important characteristic of many coastal streams is the degree of instability, related to high precipitation levels. During periods of high rain levels, individuals can be taken alone by the flow, and it can influence the sampling. P. obtusa has a morphologic structure that gives it adhesive capacity in the substrate, and it is associated with the vegetation in the edges, where the water speed was lower. It makes possible the permanence of the species in a certain extension of the stream during the floods. In the "Mergulhão" stream in January, when the rain levels were very high, only 4 fishes of P. obtusa were collected. Two hypotheses are suggested in order to explain the small occurrence of the species in this month: a) the transport of specimens down by the floods, or b) the individuals' displacement for another area of the stream.

The length amplitude of the species was the same in the three streams, yet in the "Ribeirão" stream individuals belonging to the biggest size class were not registered (class 11). Besides this, in the "Ribeirão" stream, a larger occurrence of small and intermediary sizes of fishes was observed, whereas in the other two streams, larger individuals prevailed. It is possible that the larger individuals occupy different sites from the ones sampled. São Thiago (1990) verified for Schizolecis guntheri (other Hypoptopomatinae) extensive home range in the "Parati-Mirim" stream (RJ), observing different structures in size of the population in three sampling streches. Basile-Martins et al. (1986), studying Pimelodus maculatus in three sections of the "Jaguari" and "Piracicaba" rivers (SP), reported that young concentrated in a section moved to other sections as they grew. M. S. Menezes (personal communication) reported the differentiated occurrence of young and adults of Hypostomus punctatus along the "Ubatiba" stream (RJ) and suggested that the young move stream up with the growth. Regardless of fishing method used (because the same method was used in the three sampling points no difference was in stretches of the same extension) observed that did not justify the capture of bigger individuals' in the "Mergulhão" stream.

The females of P. obtusa reached bigger lengths than the males and they were in larger number in the classes of bigger size in the three streams similar findings have been reported by other authors also (Narahara et al., 1985; Basile-Martins et al., 1986; Moraes et al., 1988). A bigger body can present advantages in relation to the individuals' fecundity and, therefore, for the population as a whole. Differentiated growth rates in sexes can explain the biggest size reached by females, as well as its prevalence in the biggest size classes (Vazzoler, 1971). This way, it is believed that males would have smaller growth rate than females, the latter reaching superior lengths. The results of the sex ratio for length classes of P. obtusa seem to suggest a differentiated growth.

The sex ratio, considering the bimonthly and the total sampling, was significantly different from 1:1. Considering the ratio in each size class, it was verified that in spite of the existence of a general prevalence of females, in the size classes 1, 2, 3, 4 and 7, the proportion approached the expected and/or males prevailed.

The condition factor (K₁) was statistically different in the three streams, and it could indicate different fat accumulations for P. obtusa in these streams. The weight of the gonads was excluded, and therefore the influence of the gonad development was practically eliminated in its values. Thus, in the "Mergulhão" and "Colônia Pereira" streams, fishes were in better condition than in the "Ribeirão" stream, where the values of the condition factor were smaller.

Similarly, the relative condition factor (Kn) was different in the studied streams, indicating that in the "Mergulhão" and "Colônia Pereira" streams, fishes were heavier than in the "Ribeirão" stream.

In general, the studied populations differed in aspects of the population structure and in values of the condition factor. The populations of P. obtusa from the "Mergulhão" and "Colônia Pereira" streams were similar, when compared to that forms the "Ribeirão" stream. Thus, it would be believed that the environmental conditions of these streams might be influencing the life histories of this species.

ACKNOWLEDGEMENTS

The authors thank Marina F. do Amaral and other friends who helped during samplings, Dr Júlio Garavelo (UFSCar) for identifying the species and CNPq for the scholarship to the D.F.Takeuti and for partial financial support (process number 52.1597/95-1)

Received: December 07, 1998;

Revised: January 11, 1999;

Accepted: May 14, 1999.

• Agostinho, A.A.; Barbieri, G.; Verani, J.R. & Agostinho, C.S. (1986), Ciclo reprodutivo e primeira maturação de Rhinelepis aspera (Agassiz, 1829)(Teleostei-Loricariidae) do rio Paranapanema. Revista Unimar, 8(1), 17-27
• Basile-Martins, M.A., Godinho, H.M., Narahara, M.Y., Fenerich-Verani, N. & Cipolli, M.N. (1986), Estrutura da população e distribuição espacial do mandi, Pimelodus maculatus Lacépède, 1803 (Osteichthyes, Pimelodidae), de trechos dos rios Jaguari e Piracicaba, São Paulo, Brasil. Boletim Instituto Pesca, 13(1),1-16
• Garutti, V. (1989), Contribuição ao conhecimento reprodutivo de Astyanax bimaculatus (Ostariophysi, Characidae), em cursos de água bacia do rio Paraná. Revista Brasileira de Biologia, 49(2), 489-495
• Le Cren, E.D. (1951), The length-weigth relationship and seasonal cycle in gonad weigth and condition in the perch (Perca fluviatilis). Journal of Animal Ecology, 20, 201-219
• Menezes, M.S. & Caramaschi, E.P. (1994), Características reprodutivas de Hypostomus grupo H. punctatus no rio Ubatiba, Maricá (RJ), sudeste do Brasil. Revista Brasileira de Biologia, 54(3), 503-513
• Moraes, M.N. de, Ferreira, A.E., Barbosa, J.M. & Rodrigues, A.M. (1988), Aspectos da estrutura populacional do peixe-cadela Galeocharax knerii (Steindachner, 1878) (Osteichthyes, Characidae) da represa de Bariri, rio Tietê, Estado de São Paulo. Boletim do Instituto Pesca, 15 (2), 179-188
• Narahara, M.Y., Godinho, H.M. & Romagosa, E. (1985), Estrutura populacional de Rhamdia hilarii (Valenciennes, 1840) (Osteichthyes, Siluriformes, Pimelodidae). Boletim do Instituto Pesca, 12(3), 123-137
• Rakocinski, C. (1988), Population structure of stream-dwelling darters: correspondence with habitat structure. Environmental Biology of Fishes, 23 (3), 215-224
• São Thiago, H. (1990), Composição e distribuição longitudinal do rio Parati-Mirim (RJ) eperíodo reprodutivo das principais espéciesMSc Thesis, Museu Nacional/Universidade Federal do Rio de Janeiro, Rio de Janeiro, 165p.
• Siegel, S. (1975), Estatística não-paramétrica (para ciências do comportamento) Mc Graw-Hill Ed., São Paulo, 350 p.
• Silva, J.X. & Souza, M.J.L. (1987), Análise Ambiental.Universidade Federal do Rio de Janeiro Ed. & Abeu Ed. Associada, Rio de Janeiro, 196 p
• Vazzoler, A.E.A. de M. (1971), Diversificação fisiológica e morfológica de Micropogon furnieri (Desmarest, 1822) ao sul de Cabo Frio, Brasil. Boletim do Instituto Oceanográfico, 20 (2), 1-70.
• Vazzoler, A.E.A. de M. (1996), Biologia da reprodução de peixes teleósteos: teoria e prática Editora da Universidade Estadual de Maringá, Maringá, 169 p
• Wooton, R.J. (1984), Introduction: Strategies and tatics in fish reproduction, pp. 1-12. in Fish Reproduction: Strategies and Tatics ed. R.J. Wooton, & G.W. Potts. Academic Press, London, 410 p.

*

Author for correspondence

Publication Dates

• Publication in this collection
  04 Mar 2011
• Date of issue
  1999

History

• Accepted
  14 May 1999
• Received
  07 Dec 1998
• Reviewed
  11 Jan 1999