nurseries and feeding areas (Welcomme, and its basin has a total area of 38,200 km2, 1979). and is situated inside Mato Grosso do Sul This work aims to emphasize the State. It is 310 km long and its general importance of the Finado Raimundo Lagoon direction is from northwest to southeast, fish nursery and its contribution to the until reaching the upper Paraná River maintenance of fish stocks in the area. floodplain, where it bends and flows parallel Specifically, our goals for this work are: (i) to the Paraná River (Paiva, 1982). This area to describe the composition of contains a great number of permanent and ichthyoplankton, emphasizing the temporary lagoons, some which are very importance of the lagoon for migratory fish large. species; (ii) to analyze the temporal The Finado Raimundo Lagoon (Fig. 1) distribution of ichthyoplankton in the littoral is located on the right margin of the (monthly) and limnetic zones (monthly and Ivinheima River (22º47’57.6”S; nictemeral); and (iii) to establish relations 53º32’29.16”W). It is elongated, with an between the organisms densities and some average depth of 3.2 m, a perimeter of 7,151.2 m and an area of 84.9 ha. A channel, environmental variables. 50 m long and 20 m wide, permanently connects with the Ivinheima River and is Material and methods separated by a levee, approximately 1 m high (Universidade Estadual de Maringá- Study area NUPÉLIA/PELD, 2000). Large macrophyte The Ivinheima River is one of the large stands, mainly Eichhornia spp., are found tributaries on the right margin of the Paraná along the entire marginal area (Personal River. This river has a meandering pattern, observation).

Figure 1: Location of the Finado Raimundo Lagoon in the upper Paraná River floodplain.

370 ZIOBER, S.R. et al. The importance of a marginal lagoon as a fish nursery in the ... Sampling and data analysis Siluriformes and Perciformes (both 0.68%) (Tab. I). There were 18 taxa belonging to Samples were taken monthly from six families, the most numerous were October 2002 to March 2003 in the littoral Characidae (eight taxa) and Anostomidae (aquatic marginal vegetation) and limnetic (three taxa). Larvae of migratory species zones of the lagoon. were not found. Captured juveniles The littoral zone was sampled with a belonged to three orders: Siluriformes strainer, which was submerged below the (79.06%), Characiformes (20.58%) and floating vegetation three times (Nakatani et Perciformes (0.36%). Characidae (eight al., 2001). The individual abundance was taxa), Anostomidae (three taxa) and expressed in capture frequency (S of the Loricariidae (three taxa) were the most number of individuals caught every month/ abundant of the 18 registered taxa. total number of individuals caught). Juveniles of migratory species were not In the limnetic zone, samplings were found (Tab. II). carried out during nictemeral cycles in four hour intervals. A conical-cylindrical plankton Limnetic zone net, with a 0.5 mm mesh, was dragged Larvae caught in the limnetic zone across the surface for 10 minutes with a (Tab. III) belonged to four orders: slow-moving boat. A plankton net, set in a Siluriformes (50.66%), Perciformes sleigh-like piece of equipment, was dragged (represented only by Plagioscion near the bottom for 15 minutes to collect squamosissimus; 24.36%), Characiformes bottom samples. Both nets were equipped (23.00%) and Gymnotiformes (represented with a flowmeter for subsequent obtaining by Eigenmannia spp.; 0.02%). A total of 34 the volume of filtered water. After samples taxa, belonging to 14 families were caught. were collected, organisms were fixed in 4% Characidae (11 taxa) and Pimelodidae (eight taxa) showed the greatest number of taxa. formalin, buffered with CaCO3 . Simultaneously, water samples were Larvae of nonmigratory species (sensu obtained to determine temperature (ºC), Suzuki et al., 2004) P. squamosissimus and dissolved oxygen (mg/L), pH and electrical Hypophthalmus edentatus were most conductivity (mS/cm) (water temperature/ abundant. They presented high densities dissolved oxygen - YSI meter, and pH/ during all sampled months, except for electrical conductivity - Digimed meter). March when there was no capture of In the laboratory, samples were sorted H. edentatus. Larvae of migratory species and larvae and juveniles were identified in (sensu Suzuki et al., 2004) Prochilodus according to the development sequence lineatus, Salminus maxillosus, Brycon technique, proposed by Ahlstrom & Moser orbygnianus, Pseudoplatystoma corruscans (1976), modified by Nakatani et al. (2001). and Sorubim lima were registered between The abundance of individuals in the December 2002 and January 2003. limnetic zone was standardized to a volu- Captured juveniles caught belonged to me of 10 m³ of filtered water, according to four orders: Perciformes (represented only Tanaka (1973), modified by Nakatani et al. by P. squamosissimus; 69.31%), Siluriformes (2001). The relation between organism (19.8%), Characiformes (7.92%) and densities and environmental variables was Gymnotiformes (represented only by E. trilineata; 2.97%). Ten taxa, belonging to evaluated using Pearson´s correlation. eight families were captured. Characidae Densities were previously transformed and Loricariidae showed the highest number [log (x+1)] to linearize relations. 10 of taxa (Tab. IV). The most abundant species, P. squamosissimus, was caught in every Results sampled month except February, and Pterygoplichthys anisitsi was caught in During the sampling period, 195 eggs, October, November and December 2002. 12,948 larvae and 378 juveniles were Juveniles of migratory species were not caught in the littoral and limnetic zones. registered.

Ichthyoplankton composition Temporal distribution Littoral Lone Littoral zone The larvae caught in this area belong During all sampling periods, fewer eggs to three orders: Characiformes (94.52%), were caught than larvae and juveniles.

Acta Limnol. Bras., 19(4):369-381, 2007 371 Table I: List of identified taxa according to Reis et al., (2003) with respective number caught (NC), frequency of occurrence (%C), mean number ± standard error (M ± SE), and months when fish larvae were collected in the littoral zone of the Finado Raimundo Lagoon, between October 2002 and March 2003. Months Taxa NC %C M + SE O N D J F M

CHARACIFORMES* 7 4.79 0.39 (+0.39) Ñ

Anostomidae** 18 12.33 1.00 (+0.62) Ñ Ñ Ñ ¨

Leporinus friderici 1 0.69 0.06 (+0.06) Ñ

Leporinus lacustris 2 1.37 0.11 (+0.11) Ñ

Leporinus spp. 29 19.86 1.61 (+0.54) Ñ Ñ ¨ Ñ ¨

Crenuchidae

Characidium spp. 1 0.69 0.06 (+0.06) Ñ

Characidae** 11 7.53 0.61 (+0.26) Ñ Ñ Ñ Ñ

Astyanax spp. 14 9.6 0.78 (+0.38) Ñ Ñ

Aphyocharax spp. 5 3.42 0.28 (+0.11) Ñ Ñ Ñ

Bryconamericus stramineus 2 1.37 0.11 (+0.08) Ñ

Hyphessobrycon sp. 7 4.79 0.39 (+0.39) Ñ

Roeboides paranensis 13 8.90 0.72 (+0.67) ¨ Ñ

Serrapinnus notomelas 3 2.05 0.17 (+0.12) Ñ Ñ Ñ

Serrasalmus maculatus 9 6.16 0.50 (+0.50) ¨

Serrasalmus spp. 9 6.16 0.50 (+0.19) Ñ Ñ Ñ Ñ Ñ

Erythrinidae

Hoplias aff. malabaricus 7 4.79 0.39 (+0.29) Ñ

SILURIFORMES

Pimelodidae

Hypophthalmus edentatus 1 0.69 0.06 (+0.06) Ñ

PERCIFORMES

Cichlidae

Crenicichla sp. 1 0.69 0.06 (+0.06) Ñ

Unidentifiable larvae 6 4.11 0.33 (+0.14) Ñ Ñ Ñ

Ñ > 0-5% ¨ > 5-10% ÿ > 10-15% · > 25% *individuals identified only up to order; **individuals identified only up to family.

372 ZIOBER, S.R. et al. The importance of a marginal lagoon as a fish nursery in the ... Table II: List of identified taxa according to Reis et al., (2003) with respective number caught (NC), frequency of occurrence (%C), mean number ± standard error (M ± SE), and months when juveniles were collected in the littoral zone of the Finado Raimundo Lagoon, between October 2002 and March 2003.

Months Taxa NC %C M + SE O N D J F M

CHARACIFORMES

Anostomidae

Leporinus friderici 5 1.81 0.28 (+0.16) Ñ

Leporinus spp. 2 0.72 0.11 (+0.08) Ñ Ñ

Schizodon borellii 1 0.36 0.06 (+0.06) Ñ

Crenuchidae

Characidium spp. 2 0.72 0.11 (+0.08) Ñ

Characidae

Aphyocharax anisitsi 1 0.36 0.06 (+0.06) Ñ

Aphyocharax spp. 4 1.44 0.22 (+0.17) Ñ Ñ Ñ

Bryconamericus stramineus 1 0.36 0.06 (+0.06) Ñ

Hyphessobrycon sp. 9 3.25 0.50 (+0.40) Ñ Ñ

Moenkhausia sanctaefilomenae 21 7.58 1.17 (+0.61) Ñ ð

Serrapinnus notomelas 7 2.53 0.39 (+0.33) Ñ Ñ

Serrapinnus spp. 2 0.72 0.11 (+0.11) Ñ

Serrasalmus marginatus 1 0.36 0.06 (+0.06) Ñ

Erythrinidae

Hoplias aff. malabaricus 1 0.36 0.06 (+0.06) Ñ

SILURIFORMES

Callichthyidae

Callichthys callichthys 1 0.36 0.06 (+0.06) Ñ

Loricariidae

Hypostomus spp. 1 0.36 0.06 (+0.06) Ñ

Loricariichthys platymetopon 1 0.36 0.06 (+0.06) Ñ

Pterygoplichthys anisitsi 216 77.99 12.00 (+3.81) ¨ ¨ · · Ñ Ñ

PERCIFORMES

Cichlidae

Crenicichla britskii 1 0.36 0.06 (+0.06) Ñ

*individuals identified only up to order; **individuals identified only up to family.

Acta Limnol. Bras., 19(4):369-381, 2007 373 Table III: List of identified taxa according to Reis et al., (2003) with respective number caught (NC), frequency of occurrence (%C), mean density (larvae/10m3) ± standard error (M ± SE), and months when fish larvae were collected in the limnetic zone of the Finado Raimundo Lagoon, between October 2002 and March 2003.

Months Taxa NC %C M + SE O N D J F M

CHARACIFORMES* 46 0.36 0.24 (+1.41) Ñ ð

Parodontidae

Apareiodon affinis 2 0.02 >0.01 Ñ

Prochilodontidae

Prochilodus lineatus 70 0.55 0.37 (+0.18) ð ð

Anostomidae** 2374 18.74 11.44 (+5.38) ð ð · · ð

Leporinus friderici 3 0.02 >0.01 Ñ

Leporinus spp. 11 0.09 0.06 (+0.08) Ñ ¨ ¨

Characidae** 82 0.64 0.39 (+0.33) ¨ ¨ Ñ

Astyanax spp. 1 0.01 >0.01 Ñ

Bryconamericus stramineus 26 0.02 0.10 (+0.05) ¨ ¨ ¨ Ñ

Hyphessobrycon sp. 1 0.01 >0.01 Ñ

Salminus maxillosus 105 0.82 0.55 (+1.00) ð ¨

Brycon orbignyanus 191 1.49 0.96 (+1.43) · ¨

Serrasalmus marginatus 1 0.01 >0.01 Ñ

Serrasalmus spp. 15 0.12 0.08 (+0.09) ¨ Ñ ¨

Cynodontidae

Rhaphiodon vulpinus 2 0.02 >0.01 Ñ

Erythrinidae** 3 0.02 0.02 (+0.002) Ñ

Hoplias aff. malabaricus 12 0.09 0.06 (+0.05) ¨ ¨ Ñ Ñ

SILURIFORMES* 46 0.36 0.22 (+0.18) ¨ ð ¨ Ñ

Callichthyidae

Hoplosternum littorale 3 0.02 0.02 (+0.01) Ñ Ñ

Loricariidae

Loricariichthys platymetopon 10 0.08 0.04 (+0.04) Ñ Ñ Ñ ¨

Pterygoplichthys anisitsi 2 0.02 >0.01 Ñ Ñ

Heptapteridae** 234 1.83 1.19 (+1.75) · ¨ Ñ

Ñ 0>1 ind./10m3 ¨ 0>10 ind./10m3 ð 10>50 ind./10m3 · >50 ind./10m3 *individuals identified only up to order; **individuals identified only up to family. Underline= long distance migrators taxa.

374 ZIOBER, S.R. et al. The importance of a marginal lagoon as a fish nursery in the ... Table III: Cont. Months Taxa NC %C M + SE O N D J F M

Pimelodidae** 39 0.30 0.19 (+0.15) ¨ ¨ Ñ

Hypophthalmus edentatus 6034 47.13 21.37 (+4.45) · · · · ·

Iheringichthys labrosus 3 0.02 0.01 (+0.02) Ñ Ñ

Megalonema platanum 3 0.02 0.01 (+0.02) Ñ Ñ

Pseudoplatystoma corruscans 84 0.66 0.39 (+0.32) ¨ ð

Sorubim lima 8 0.06 0.04 (+0.06) Ñ

Zungaro zungaro 4 0.03 0.02 (+0.08) Ñ Doradidae Pterodoras granulosus 13 0.10 0.04 (+0.08) Ñ Auchenipteridae Auchenipterus osteomystax 1 0.01 >0.01 Ñ

Tatia neivai 1 0.01 >0.01 Ñ Ñ GYMNOTIFORMES Sternopygidae Eigenmannia spp. 2 0.02 0.01 (+0.01) Ñ PERCIFORMES Sciaenidae Plagioscion squamosissimus 3119 24.36 10.15 (+1.26) Ñ Ñ Ñ Ñ Ñ Ñ

Unidentifiable larvae 244 1.90 1.07 (+0.45) Ñ Ñ Ñ Ñ Ñ Ñ

Yolk-sac larvae 5 0.04 0.02(+0.02) Ñ Ñ

Ñ 0>1 ind./10m3 ¨ 0>10 ind./10m3 ð 10>50 ind./10m3 · >50 ind./10m3 *individuals identified only up to order; **individuals identified only up to family. Underline= long distance migrators taxa.

Table IV: List of identified taxa according to Reis et al., (2003) with respective number caught (NC), frequency of occurrence (%C), mean density (juvenile/10m3) ± standard error (M ± SE), and months when juveniles were collected in the limnetic zone of the Finado Raimundo Lagoon, between October 2002 and March 2003. Months Taxa NC %C M + SE O N D J F M

Bryconamericus stramineus 1 0.99 >0.01 Ñ

Hyphessobrycon sp. 4 3.96 0.01 (+0.01) Ñ Ñ Ñ

Roeboides paranensis 3 2.97 0.01 (+0.01) Ñ Ñ

SILURIFORMES Loricariidae

Loricariichthys platymetopon 4 3.96 >0.01 ¨

Pterygoplichthys anisitsi 11 10.89 0.04 (+0.03) ¨ ¨

Acta Limnol. Bras., 19(4):369-381, 2007 375 Table IV: Cont.

Months Taxa NC %C M + SE O N D J F M

Heptapteridae* 1 0.99 >0.01 Ñ

Pimelodidae Ñ

Hypophthalmus edentatus 3 2.97 >0.01 Ñ

Auchenipteridae

Tatia neivai 1 0.99 >0.01 Ñ GYMNOTIFORMES Sternopygidae Eigenmannia trilineata 3 2.97 0.01 (+0.02) Ñ PERCIFORMES Sciaenidae

Plagioscion squamosissimus 70 69.31 0.24 (+0.09) ¨ ¨ ¨ ¨ ¨ Ñ 0>1 ind./10m3 ¨ 0>10 ind./10m3 ð 10>50 ind./10m3 · >50 ind./10m3 *individuals identified only up to family.

In October and November 2002 and February Limnetic Zone 2003, the number of captured larvae was High egg mean densities occurred at higher than juveniles; the opposite trend the water surface and at the bottom during was observed during other months (Fig. 2). November and December 2002 and

120 Eggs 100 Larvae Juveniles

80

60

40

20 Number of individuals caught

0 Oct/02 Nov/02 Dec/02 Jan/03 Feb/03 Mar/03 Months

Figure 2: Number of fish eggs, larvae and juveniles collected in the littoral zone of Finado Raimundo Lagoon, Ivinheima River, Mato Grosso do Sul State, between October 2002 and March 2003.

January 2003. At the surface, the greatest mainly between October and December mean density was verified in November 2002 and January 2003. The greatest mean (2.36 eggs/10m3 ) (Fig. 3A). Larvae were density at the surface was verified in abundant in every sampled month. November (0.93 juveniles/10m3), while the However, the greatest mean densities at greatest mean density near the bottom was the surface and near the bottom were verified in October (0.83 juveniles/10m3 ) observed in December, with 110.68 larvae/ (Fig. 3C). 10m3 and 107.94 larvae/10m3 , respectively In relation to nictemeral variation, (Fig. 3B). Juveniles densities were highest high egg mean densities were obtained

376 ZIOBER, S.R. et al. The importance of a marginal lagoon as a fish nursery in the ... during the night at the surface, especially bottom, the greatest mean density was at 12:00 a.m. (1.57 eggs/10m3 ). Near the noted at 4:00 a.m. (0.94 eggs/10m3) (Fig. 4A).

3.5 180 A B Surface Surface 150 2.8 Bottom Bottom )

) 3 3 120 2.1 90 1.4 60

0.7 Mean density (eggs/10m

Mean density (larvae/10m 30

0.0 0 Oct/02 Nov/02 Dec/02 Jan/03 Feb/03 Mar/03 Oct/02 Nov/02 Dec/02 Jan/03 Feb/03 Mar/03 Months Months 1.6 C Surface Bottom ) 3 1.2

0.8

0.4 Mean density (juveniles/10m

0.0 Oct/02 Nov/02 Dec/02 Jan/03 Feb/03 Mar/03 Months Figure 3: Monthly variations of mean fish eggs (A), larvae (B) and juveniles (C), at the surface and bottom of Finado Raimundo Lagoon, Ivinheima River, Mato Grosso do Sul State, between October 2002 and March 2003 (markers=mean, bars= standard error).

3.0 200 A Surface B Surface Bottom Bottom 2.4 160 ) ) 3 3

1.8 120

1.2 80

0.6 40 Mean density (eggs/10m Mean density (larvae/10m

0.0 0 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 Hours Hours 2.4

C Surface Bottom ) 3 1.8

1.2

0.6 Mean density (juveniles/10m

0.0 8:00 12:00 16:00 20:00 0:00 4:00 Hours Figure 4: Daily variations in mean densities of fish eggs (A), larvae (B) and juveniles (C), at the surface and bottom of Finado Raimundo Lagoon, Ivinheima River, Mato Grosso do Sul State, between October 2002 and March 2003 (markers=mean, bars= standard error).

Acta Limnol. Bras., 19(4):369-381, 2007 377 The greatest mean larvae densities occurred the smallest in October (Fig. 5A). An inverse during the night at the surface, mainly at 12:00 tendency was observed for dissolved oxygen, a.m. (104.94 larvae/10m3). Near the bottom, with greater values in October and smaller in intense variations between times were not February (Fig. 5B). The pH also showed a noticed. The smallest mean density was 39.35 tendency similar to dissolved oxygen, with larvae/10m3 at 12:00 p.m. and the greatest was higher values in October and lower in February 67.41 larvae/10m3 at 4:00 a.m. (Fig. 4B). and March (Fig. 5C). Mean electrical conductivity Juveniles were also more abundant at night, did not present great alterations during the with greatest mean density near the bottom at sampled period. Great mean values were noted 8:00 p.m. (1.19 individuals/10m3). At the surface, in January and low values were noted in the greatest mean density was 0.66 individuals/ November (Fig. 5D). 10m3, observed at 12:00 a.m. (Fig. 4C). Dissolved oxygen presented significant positive correlation with egg densities, Relationship between environmental whereas water temperature was negatively variables and individuals densities correlated with larvae. Juvenile density did The greatest mean values of water not show significant correlation to the temperature were obtained in February, and variables considered (Tab. V).

34 10 A Surface B Surface Bottom Bottom 32 8 C) o 30 6

28 4 Water temperature (

26 Dissolved oxigen (mg/l) 2

24 0 Oct/02 Nov/02 Dec/02 Jan/03 Feb/03 Mar/03 Oct/02 Nov/02 Dec/02 Jan/03 Feb/03 Mar/03 Months Months 7.8 54 C Surface D Surface Bottom Bottom 7.4 50

7.0 46 pH 6.6 42

6.2 38 Electrical condutivity (µS/cm)

5.8 34 Oct/02 Nov/02 Dec/02 Jan/03 Feb/03 Mar/03 Oct/02 Nov/02 Dec/02 Jan/03 Feb/03 Mar/03 Months Months Figure 5: Mean values (+ standard error) of water temperature (A), dissolved oxygen (B), pH (C) and electrical conductivity (D), obtained at the surface and bottom of Finado Raimundo Lagoon, Ivinheima River, Mato Grosso do Sul State, between October 2002 and March 2003.

Table V: Pearson’s correlations (R) between environmental variables and log-transformed values (log x+1) of eggs, larvae and juveniles densities for the Finado Raimundo Lagoon, Ivinheima River, Mato Grosso do Sul State. In parentheses are the values of the probability associated with R.

Water Dissolved Electrical Variables pH Temperature oxygen conductivity

Eggs density -0.14 (ns*) 0.32 (0.007) 0.20 (ns*) -0.17 (ns*)

Larvae density -0.42 (0.000) -0.01 (ns*) -0.08 (ns*) -0.01 (ns*)

Juveniles density -0.23 (ns*) 0.19 (ns*) 0.07 (ns*) -0.21 (ns*) ns*= non-significant (p<0.05).

378 ZIOBER, S.R. et al. The importance of a marginal lagoon as a fish nursery in the ... Discussion December to January for B. orbygnianus; and from November to December for S. lima. The presence of these species likely In the upper Paraná River floodplain, indicates that they spawn in the main the period of reproductive fish activity channel of the Ivinheima River and their extends from October to March (Vazzoler, fertilized eggs and/or hatched larvae drift 1996) and corresponds to a period of high to the lake to complete development. eggs and larvae densities (Nakatani et al., Reynalte-Tataje et al. (2005) registered 1997; Baumgartner et al., 1997). A larvae of P. corruscans drifting along the considerable enrichment of water occurs Ivinheima River and concluded that this during this period, due to decomposition species uses the Finado Raimundo Lagoon of organic matter present in the plain, which as a development area. favors the development of phyto- and Juveniles presented the greatest zooplankton. These organisms are intensely abundance in the littoral zone. Several exploited by fish in their initial phases, and species with juvenile individuals also therefore when abundant, they contribute registered as larvae, indicating that these to the accelerated growth of fish larvae species are completing their life cycle in (Esteves 1998; Makrakis et al. 2005). this environment. The most abundant Our results showed that egg densities species was P. anisitsi, but larvae were not were low when compared to larvae. This captured possibly due to the development may be a result of the great proportion of of parental care, common in the family species that develop parental care (egg- Loricariidae (Nakatani et al., 2001). Juveniles bearing), such as Crenicichla spp., Hoplias of migratory species were not caught; aff. malabaricus, Hoplostenum littorale, maybe because in during life stage, they Loricariichthys platymetopon and have already left the lake to continue their Serrasalmus spp. (Vazzoler, 1996). Most of life cycle in the main channel of the river. these species have adhesive eggs (which However, it is difficult to capture these stay fixed on a substrate), or build nests individuals using a plankton net, because for egg deposition, which are difficult to they can escape from the sampling gear. capture with the sampling gear used. Delariva et al. (1994) also noticed a low Bilkovic et al. (2002) characterized spawning incidence of migratory species in marginal reaches as shallow, with high vegetated areas at the floodplain of the concentrations of dissolved oxygen and with upper Paraná River, stressing the need to relatively high water current. However, these better study the importance of these areas environmental characteristics do not apply as a nursery for these species. to lagoons, making it difficult to classify High densities in general, occurred them as an appropriate environment for during the night. Densities of eggs were hatching, especially for migratory species higher at night at the surface. According to with pelagic eggs, which need constant Graaf et al. (1999), spawning is induced by oxygenation to develop properly. a reduction of light. Neotropical species Larvae of P. squamosissimus and H. generally spawn at sunset, when water edentatus (non-migratory species) were temperature is higher (Godoy, 1975). For most abundant and are typical of lentic Vazzoler (1996), light and temperature are environments. The high abundance of both cues for fish reproduction because they species is attributed to their great fecundity, affect hormonal production that culminates great adult population, low larvae mortality in spawning. and the fact that eggs and larvae are Larvae were also more abundant at pelagic, which favors dispersion at the night at the surface; during the day, they surface, as reported by Bialetzki et al. were almost exclusively captured near the (2005). bottom. Baumgartner et al. (1997) also Larvae of migratory species were also observed this tendency in some caught ( P. lineatus, S. maxillosus, B. environments of the upper Paraná River orbygnianus, P. corruscans and S. lima). They floodplain. Vertical migration of larvae can were caught in periods that coincided with occur during the day because of the great their reproductive period (Vazzoler, 1996), food availability at the surface during the which extends from November to February night, resulting from zooplankton migration for P. lineatus and P. corruscans; from (Castro et al., 2002). During the day, larvae October to January for S. maxillosus; from remain near the bottom, protected from vi-

Acta Limnol. Bras., 19(4):369-381, 2007 379 sual predators. Juveniles for instance, were support, PIE/PELD/CNPq and CNPq (Process more abundant during the night because number 476162/2004-1) for making the in the absence of light, avoiding the project possible, PIBIC/UEM for awarding a sampling gear is much more difficult. study grant, our friends Sebastião Therefore, capture is considered accidental. Rodrigues, Alfredo Soares and Valmir Alves Larvae densities had a negative Teixeira for assistance with the fieldwork correlation with water temperature. Milder and our friends from Ichthyoplankton temperatures were registered in months Laboratory (Nupélia/UEM) for helping with with greatest larvae densities (the spawning the fieldwork and laboratory analyses. period of most species). In the following months (February-March), when temperature References increased, the reproductive activity had possibly already decreased. Migratory Agostinho, A.A. & Júlio Jr., H.F. 1999. Peixes species were absent in the months when da bacia do alto rio Paraná. In: Lowe- temperatures were high. According to McConnel, R.H. (ed.) Estudos ecológicos Herzig & Winkler (1986), the initial stages of de comunidades de peixes tropicais. species that live and spawn in lakes seem EDUSP, São Paulo. p.374-400. to be more tolerant to great variations in Ahlstrom, E.H. & Moser, H.G. 1976. Eggs and temperature than species that show strong larvae of fishes and their role in migratory tendencies. systematic investigations and in Egg densities showed a positive fisheries. Rev. Trav. Inst. Peches Marit., correlation to the concentration of dissolved 40:379-398. oxygen. According to Werner (2002), Baumgartner, G., Nakatani, K., Cavicchioli, dissolved oxygen is the most important M. & Baumgartner, M.S.T. 1997. Some chemical variable that determines habitat aspects of the ecology of fish larvae in for the early life stage of fish. Fuiman (2002) the floodplain of the high Paraná River, says that low oxygen levels can result in a Brazil. Rev. Bras. Zool., 14:551-563. shorter incubation period and smaller, less Bialetzki, A., Nakatani, K., Sanches, P.V., developed larvae at hatching, which may Baumgartner, G. & Gomes, L.C. 2005. increase mortality. However, it is possible Larval fish assemblage in the Baía River that spawning occurs in areas with high (Mato Grosso do Sul State, Brazil): tem- dissolved oxygen concentrations. poral and spatial patterns. Environ. Biol. Other variables (electrical conductivity Fishes, 73:37-47. and pH) did not show significant correlation Bilkovic, D.M., Hershner, C.H. & Olney, J.E. with densities, in spite of Vazzoler (1996), 2002. Macroscale assessment of who considered the electrical conductivity American shad and nursery habitats in as an important synchronizing factor for fish the Mattaponi and Pamunkey Rivers, spawning. The pH does not have an Virginia. N. Am. J. Fish. Manage., 22:1176- established relationship with fish 1192. reproduction. Baumgartner et al. (1997) Castro, R.J., Nakatani, K., Bialetzki, A., concluded that this variable is not so Sanches, P.V. & Baumgartner, G. 2002. important as larvae abundance. Temporal distribution and composition of The Finado Raimundo Lagoon is an the ichthyoplankton from Leopoldo’s Inlet important habitat for fish reproduction. It is on the Upper Paraná River floodplain also an adequate place for the development (Brazil). J. Zool., 256:437-443. Delariva, R.L., Agostinho, A.A., Nakatani, K. of the initial phases, either for resident or & Baumgartner, G. 1994. Ichthyofauna migratory species. Therefore, this lake associated to aquatic macrophytes in the contributes to the recruitment of fish species upper Paraná River floodplain. Rev. in the area, emphasizing the importance of Unimar, 16:41-60. lagoons for the maintenance of the species Esteves, F.A. 1998. Fundamentos de in the upper Paraná River basin. limnologia. Interciência, Rio de Janeiro. 602p. Acknowledgements Fuiman, L.A. 2002. Special considerations of fish eggs and larvae. In: Fuiman, L.A. We extend our thanks to the Núcleo de & Werner, R.G. (eds.) Fishery science: the Pesquisas em Limnologia, Ictiologia e unique contributions of early life stages. Aqüicultura (Nupélia/UEM) for logistical Blackwell Publishing, Oxford. p.1-32.

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