Population parameters of the fish fauna in a long‐established Amazonian reservoir (Amapá, Brazil)

(1)

Population parameters of the fish fauna in a long-established Amazonian reservoir

(Amap

a, Brazil)

By J. C. Sa-Oliveira1

, R. Angelini2and V. J. Isaac-Nahum3

1_{Ichthyology and Limnology Laboratory, Federal University of Amapa, Macapa, Brazil;}2

Departamento de Engenharia Civil, Universidade Federal do Rio Grande do Norte, Natal, Brazil;3Fishery Biology Laboratory, Federal University of Para -UFPA- Campus Guama, Belem, Brazil

Summary

The present study focused on the fish fauna of the 44-year-old Coaracy Nunes reservoir in the northern Amazon basin, producing estimates of the growth constant (k), maximum and asymptotic body lengths and weights, natural mortality (M), the consumption/biomass ratio (QB) (intake of food by a group over a year), the Aspect ratio (Ar) of the caudal fin, growth performance (Φ), longevity, and trophic level for 45 fish species. Species collection was divided into eight sampling campaigns between May 2009 and July 2010. Gill-nets were used in four of the sampling sites. The results revealed that (i) the most predominant species are Ageneio-sus ucayalensis, Hemiodus unimaculatus, Serrasalmus gibbus and Geophagus proximus; (ii) small and medium-sized fishes predominated in the community, characterized by high rates of growth and natural mortality, consistent with a predomi-nance of r-strategists; (iii) the body lengths of the detritivore species were similar to those of the piscivores, which are normally larger, but with higher growth rates, more similar to those recorded for the omnivores; (iv) consumption/bio-mass ratio (QB)9 body length relationship is higher in the detritivores than in the omnivores and piscivores (which were similar to each other). Overall, the reservoir habitat appears to be advantageous to detritivorous fish species.

Introduction

Estimates of population parameters are important indicators of the viability and sustainability of fish populations susceptible to fishery activities (Froese and Binohlan, 2000). These parameters are also necessary for the construction of trophic models for species using an Ecopath approach (Christensen and Pauly, 1992), which can be essential for the development of effective fishery management programs (Angelini et al., 2013).

Fish populations may respond to environmental variables in different ways. In addition to the life-history characteris-tics of the species, these responses may be influenced by the type of habitat and the duration and intensity of the fluctua-tions in the environment, which may affect physiological con-ditioning being reflected ultimately in population parameters (Vazzoler, 1996; Agostinho et al., 1997).

Parameters such as von Bertalanﬀy’s growth index, asymp-totic length and weight, natural mortality coeﬃcients, the

aspect ratio of the caudal fin, consumption/biomass ratios, and even weight-length ratios are fundamentally important for the development of ecosystem-level analytical approaches and the upgrading of ecological models (Angelini and Agost-inho, 2005; Gubiani et al., 2011). In addition, the calculation of trophic levels and the classification of the species in feed-ing guilds provide an essential understandfeed-ing of resource par-titioning and the distribution of niches within a fish assemblage (Sa-Oliveira et al., 2014).

Despite the importance of these parameters, estimates of somatic growth rates are available for only approximately 5% of ﬁsh species worldwide (Binohlan and Pauly, 2000), a pro-portion probably even lower for Neotropical fauna (Froese and Pauly, 2011). Predictably, no data are available for ﬁsh populations inhabiting the Coaracy Nunes reservoir, the old-est hydroelectric scheme in the Brazilian Amazon basin, which was built in 1975 on the Araguari River in Amapa State.

The present study estimated the major population parame-ters for fish species inhabiting this Amazonian reservoir. These parameters are analyzed comparatively among the dif-ferent trophic guilds for the identification of ecological pat-terns and a more systematic understanding of the partitioning of feeding resources in the reservoir, 40 years after it was originally flooded.

Materials and methods

Study area

The Coaracy Nunes reservoir, located on the middle Aragua-ia River in the northern BrazilAragua-ian state of Amapa (Fig. 1), was ﬂooded in 1970. The reservoir covers a total area 23.5 km², has a mean discharge of 976 m³ s1_{, mean depth}

of 15 m, and a total volume of 138 Hm³. The local climate is typical of the Amazon basin, with a rainy season between January and June, and a dry season from July to December (Bezerra et al., 1990; IBGE, 2010; ANA, 2011). The vegeta-tion of the region is characterized by elements of tropical rainforest, savannah, and ﬂoodplain swamps.

Data collection

Fish specimens were collected from the reservoir by stan-dardized samplings with eight gillnets (mesh sizes of 10, 20,

U.S. Copyright Clearance Centre Code Statement:0175-8659/2015/3102–290$15.00/0

Applied Ichthyology

(2)

30, 50, 60, 70, 80, 100 mm opposite knots) every 2 months between May 2010 and July 2011. Four samplings were con-ducted in the ﬂood season and four in the dry season. Nets were set in sampling areas for 24 h (checked at 08.00, 16.00 and 22.00 hours). The specimens were kept on ice in a cooler and transported immediately to the laboratory for measure-ment and analysis. The total length (mm) and weight (g) of each specimen were recorded. In this analysis, we did not dis-tinguish for sex or maturity status.

Data analysis

Population parameters were estimated for 45 species of fish found in the reservoir. Growth rates were calculated using von Bertalanffy’s equation, Lt¼ L1 ð1 ekðtt0ÞÞ, where Ltis the length of the fish (cm) at age t, L∞is the asymptotic

length (cm), k is the constant growth rate (year1), and t0 is

the nominal age at which ﬁsh length is considered to be zero. The constant k was calculated in the FISAT software

(FAO-ICLARM, 1996; Gayanilo and Pauly, 1997) using the ELE-FAN I routine (Pauly and David, 1981), which is based on the modal displacement of the time series of the length classes, providing an index of growth rates in the diﬀerent age classes. The value of L_∞ was found using the length of the largest individual (Lmax) and Froese and Binohlan’s (2000) equation:

log (L_∞)= 0.044 + 0.9841 9 log (Lmax). To standardize the

data, t0was considered to be zero for all populations.

The coeﬃcient of natural mortality (M) was derived from Pauly’s (1980) empirical formula: M= k0.659 L_∞0.2799 T0.463, where T is the temperature (28°C). The consumption/

biomass ratio (QB) was estimated using Palomares and Pauly’s (1998) empirical regression: log (QB)= 7.964 0.204 9 log(W∞) 1.965 9 (T0)+ 0.083 9 Ar + 0.532 9

H+ 0.398 9 D, where QB is the consumption/biomass ratio, W_∞ is the asymptotic weight (g), T0 is the inverse of the mean annual temperature of the water (T0= 1000/ 28°C + 273.15), Ar is the aspect ratio of the caudal fin (Ar= h2/S, where: h is the height, in mm, and S is the sur-face area of the caudal fin, in mm2), which provides a mea-sure of the swimming effort and metabolic activity of a fish species (Palomares and Pauly, 1998). The Ar values were derived from measurements of at least five specimens of dif-ferent sizes per species. The H and D parameters refer to the feeding behavior of the species, where H= 1 indicates an herbivore, D = 1, a detritivore, and all other groups are H= D = 0.

The relationship between weight and length was based on the equation W= a 9 Lb, where W is the weight (g) and L is the length (cm) of the specimen. The parameters a and b were calculated by exponential regression and the asymptotic weight was calculated subsequently by W₁¼ a L₁b_.

Lon-gevity (tmax), deﬁned as the time that an individual takes to

reach 95% of the asymptotic length, was estimated using the formula proposed by Taylor (1958): tmax= t0+ 2.996/k. The

growth performance index (Φ) was used to compare the growth curves of the specimens of all of the species, based on the equation of Pauly and Munro (1984), whereΦ = log (k)+ 2 9 log (L_∞).

Trophic classification of the specimens was based on the analysis of the stomach contents, as described in Sa-Oliveira et al. (2014). The categories were used here for the compara-tive analysis of a number of the statistical parameters pre-sented above. The species were classified in five trophic guilds: (i) herbivore (predominance of leaves, fruits, flowers, seeds and algae in the diet); (ii) piscivore (predominance of fish); (iii) carnivore (arthropods and prey other than fish); (iv) omnivore (balanced diet of plant and animal material); (v) detritivore (feeds predominantly on detritus or sedi-ments). The trophic level was determined based on the equa-tion TL= [1 + (weighted mean of the TL of the prey)] considering TL= 1 for detritus, algae, and plants (Angelini and Gomes, 2008).

The population parameters of the species were ordinated in a Principal Coordinates Analysis (PCO), run in the PRI-MER 6+ software (Clarke and Gorley, 2006), in order to

elucidate the similarities in their population strategies and in particular, how these parameters vary among trophic categories. The data were standardized and Euclidian dis-tance was used as a measurement of their similarity. Only species for which all the population parameters had been estimated were included in this analysis. Analyses of Vari-ance (ANOVA), and Tukey post hoc tests, when necessary,

were used to compare each parameter among the diﬀerent trophic categories.

Simple linear regression models were used to verify the relationship between the consumption/biomass ratio (QB) and the asymptotic length of the diﬀerent trophic categories. The slopes of these regressions were compared using an

ANCOVA.

Fig. 1. Study region of Coaracy Nunes Reservoir (northern Brazil-ian state of Amapa), May 2009 to July 2010

(3)

Table 1 Pop ulation par ameters o f fish species in C oaracy Nu nes hyd roelectric reservo ir, Am ap aState (Bra zil): n, numbe r o f specim ens; Lt Range : minimum and max imum len gth (mm ); k , von Bertalan ffy’s gro wth consta nt; Lmax , maximum lengt h; L∞ , asymp totic length; W max , max imum weight ; W ∞ , asymp totic weight; Long, Long evity ; Ar, Aspec t ratio of caud al fin; M , co ef-ficien t o f natural mort ality; QB, co nsumptio n/biom ass ratio; Φ , grow th pe rforman ce index ; R 2 , coefficie nt of len gth-we ight regr ession ; a and b , consta nts of length-we ight regression; TL, trophic level and Troph, trop hic cate gory: Pi sc-piscivorous; Omn, omniv ore; C arn, carni vorous; De tr, detr itivores; He rb, he rbivores Nome Cient ıfico n Lt Ran ge kL max Loo W max W oo Long Ar M QB Φ ab R 2 NT Trop h Ace strorhync hus falca tus (B loch, 1794 ) 22 110 –126 0.47 20.0 21.10 231 267.0 0 6.37 2.15 1.03 12.71 2.32 0.002 2.81 0.97 3.21 Pi sc Ace strorhync hus falciro stris (Cuv ier, 1819) 92 198 –306 0.39 23.1 24.32 196 249.0 0 7.68 2.67 0.90 14.23 2.36 0.037 2.50 0.74 3.27 Pi sc Agen eiosus iner mis (Linnae us, 1766 ) 10 152 –470 0.32 58.7 60.89 1580 3305 .39 9.36 0.71 5.04 3.07 0.013 3.02 0.50 3.10 Pi sc Agen eiosus uca yalensis (C astelnau, 1855 ) 281 114 –540 0.54 21.1 22.24 1756 1922 .84 5.55 2.5 0.74 9.08 2.43 0.003 3.22 0.83 3.14 Pi sc Astyana x bima culatus (L innaeus, 1758 ) 57 96 –127 0.6 12.7 13.50 103 117.0 0 4.99 1.14 1.57 12.40 2.04 0.011 2.78 0.90 2.13 Om n Auch enipt erus nuc halis (Spix & Agassi z, 1829 ) 10 108 –229 0.53 22.9 24.11 90.37 108.0 0 5.65 1.8 1.23 14.29 2.49 0.008 2.91 0.90 3.00 Carn Bivibranch ia notata (Vari & Gouldi ng, 1985) 17 150 –195 0.55 19.5 20.58 55 57.77 5.45 1.37 51.01 2.37 0.88 2.00 De tr Boulen gerella cuv ieri (A gassiz, 1829 ) 54 310 –804 0.36 46.2 48.10 3434 3848 .22 8.32 1.97 0.49 7.12 2.92 0.009 3.05 0.87 3.35 Pi sc Chae tobran chus flaves cens (He ckel, 1840) 14 78 –116 0.54 11.6 12.35 50 58.60 5.55 0.67 1.27 13.05 1.92 0.04 2.95 0.95 2.30 Om n Chara x gibbosus (L innaeus, 1758 ) 57 69 –225 0.53 22.5 23.70 85 92.52 5.65 1.5 1.23 13.93 2.47 0.064 2.46 0.65 2.84 Pi sc Cichla ocellaris ( B loch & Schn eider, 1801 ) 28 180 –524 0.23 74.0 76.47 7310 8867 .00 13.03 1.45 0.51 5.44 3.13 0.003 3.40 0.95 3.40 Pi sc Curima ta inorn ata (Vari, 1989) 81 88 –317 0.5 31.7 33.20 370 398.0 0 5.99 1.69 1.08 26.82 2.74 0.063 2.50 0.90 2.00 De tr Cypho charax gould ingi (Vari, 1992 ) 11 115 –126 0.58 14.7 15.59 36 50.49 5.17 1.53 11.83 2.15 0.013 3.02 0.40 2.06 Om n Geop hagus prox imus (Caste lnau, 1855) 120 90 –251 0.52 16.6 17.57 222 230.0 0 5.76 1.09 1.18 10.70 2.21 0.055 2.54 0.88 2.21 Om n Glyptop eric hthys joselimaianus (Web er, 1991) 8 165 –260 0.49 30.5 31.97 206 289.2 6 6.11 1.17 1.08 25.92 2.70 0.70 2.00 De tr Har ttia duriv entris (Rap Py-Danie l & Oliveira, 2001 ) 22 114 –214 0.54 21.4 22.56 78 85.39 5.55 0.96 1.27 31.93 2.44 0.03 2.47 0.72 2.00 De tr Hemiod us micr olepis (K ner, 1858 ) 14 155 –278 0.5 27.8 29.18 156 159.4 8 5.99 1.77 1.12 32.82 2.63 0.87 2.00 De tr Hemiod us unim aculat us (Bloch , 1794) 253 80 –258 0.65 17.4 18.40 154 177.6 1 4.61 1.64 1.15 12.53 2.34 0.71 2.34 Om n Hopli as aimara (V alencienne s, 1847 ) 23 211 –600 0.12 100 102.8 5 1 3 969 15 200 24.97 1.2 0.32 4.65 3.10 0.006 3.14 0.95 3.45 Pi sc Hopli as macroph thalmu s (Pellegrin, 1907) 9 305 –893 0.15 89.3 92.01 8490 8648 .28 19.97 0.37 4.14 3.10 0.60 3.47 Pi sc Hypost omus ema rgina tus (Vale ncienne s, 1840) 4 265 –270 0.48 32.0 33.51 336 391.0 0 6.24 2.18 1.05 29.56 2.73 0.003 3.37 0.90 2.00 De tr Hypost omus plec ostomu s (Linnae us, 1758) 25 156 –270 0.5 27.0 28.35 200 216.0 2 5.99 1.18 0.93 27.56 2.60 0.016 2.84 0.85 2.00 De tr Laemo lyta petiti (G ery, 1964 ) 9 168 –178 0.52 23.1 24.32 71 94.40 5.76 1.26 1.24 13.25 2.49 0.87 2.07 Om n Lepori nus af. para e (Eigen mann, 1908) 24 153 –300 0.5 30.1 31.55 358 413.5 5 5.99 1.36 1.10 9.99 2.70 0.006 3.23 0.94 2.08 Om n Lepori nus affinis (G €unther, 1864) 36 143 –356 0.44 37.6 39.28 482 538.0 0 6.81 2.38 0.95 11.51 2.83 0.02 2.73 0.80 2.14 Om n Mega lonema platyc ephalum (E igenman n, 1912 ) 6 195 –360 0.53 23.0 24.21 92 100.9 2 5.65 1.27 10.27 2.49 0.031 2.54 0.94 3.20 Pi sc Moen khausia chry sargyrea (G €unthe r, 1864 ) 17 77 –158 0.58 14.8 15.69 17 18.54 5.17 1.53 14.52 2.15 0.90 3.14 Carn Myleu s rhom boidalis (C uvier, 1818 ) 6 100 –445 0.4 44.5 46.36 1884 2379 .36 7.49 0.88 18.35 2.93 0.02 3.04 0.95 2.00 He rb Pachy pops fourc roi (La Cep ede, 1802 ) 8 126 –173 0.52 25.0 26.29 98 110.6 3 5.76 1.38 1.18 13.13 2.56 0.51 3.00 Pi sc Peckolt ia oligo spila (G €unther, 1864 ) 24 123 –225 0.53 22.5 23.70 134 152.0 2 5.65 0.95 1.23 28.33 2.47 0.83 2.00 De tr Pellona flavipin nis (Vale ncienne s, 1836 ) 8 143 –157 0.24 73.0 75.46 2510 2847 .00 12.48 1.59 0.53 7.04 3.14 0.88 3.15 Pi sc Piarac tus brac hypomus (C uvier, 1818 ) 5 445 –555 0.33 57.2 59.35 2714 265.6 1 9.08 0.73 8.43 3.07 0.97 2.22 Om n Pim elodus bloc hii (Valencienn es, 1840 ) 23 145 –245 0.52 24.5 25.77 128.5 140.0 0 5.76 1.41 1.19 12.58 2.54 0.015 2.82 0.73 3.20 Pi sc Pim elodus orna tus (Kne r, 1858 ) 73 127 –395 0.49 38.5 40.20 460 464.0 0 6.11 2.5 1.01 12.14 2.90 0.034 2.57 0.76 3.22 Pi sc Plagiosc ion squa mosissimus (He ckel, 1840) 12 227 –416 0.41 41.6 43.39 930 5175 .00 7.31 1.02 0.79 5.59 2.89 0.02 2.85 0.81 3.10 Carn Psectro gaste r af. falca ta (E igenman n, 1889 ) 77 103 –335 0.48 33.5 35.06 400 412.0 0 6.24 2.21 1.03 29.41 2.77 0.052 2.51 0.83 2.00 De tr Pseuda canth icus spino sus (Caste lnau, 1855 ) 14 160 –325 0.47 32.5 34.03 380 457.1 0 6.37 1.03 1.03 22.98 2.74 0.005 3.26 0.77 2.00 De tr Retroc ulus lapidi fer (Caste lnau, 1855) 5 212 –225 0.49 29.5 30.94 424 445.7 1 6.11 1.9 1.09 10.91 2.67 0.90 2.12 Om n Retroc ulus septentrionalis (Gosse , 1971 ) 47 0– 223 0.53 23.3 24.53 150 173.0 0 5.65 1.92 1.22 13.28 2.50 0.95 2.26 Om n Roeb oides affin is (G €unthe r, 1868 ) 33 111 –203 0.54 20.3 21.41 90.44 105.0 0 5.55 1.2 1.28 12.82 2.39 0.024 2.70 0.84 2.74 Carn Satanop erca acu ticep s (Hecke l, 1840 ) 12 112 –185 0.55 18.5 19.54 83.35 88.00 5.45 1.03 1.33 12.86 2.32 0.04 2.60 0.90 2.11 Om n Serra salmu s gibbus (C astelnau, 1855 ) 208 85 –350 0.46 35.0 36.60 306 364.6 4 6.51 2.63 1.00 13.07 2.79 0.023 2.81 0.83 3.32 Pi sc Tomete s triloba tus (V alencie nnes, 1850 ) 15 148 –476 0.41 47.5 49.43 5435 6250 .00 7.31 2.88 0.86 26.14 3.00 0.031 3.00 0.95 2.00 He rb Triport heus angu latus (Spix & A gassiz, 1829 ) 28 143 –253 0.51 25.3 26.60 178.1 6 182.0 0 5.87 2.27 1.16 14.06 2.56 0.009 3.05 0.87 2.10 Om n Triport heus trifu rcatus (Castel nau, 1855 ) 5 172 –219 0.53 21.9 23.07 86 92.90 5.65 1.29 10.45 2.45 0.98 2.15 Om n

(4)

Results

Parameters were estimated for all of the principal fish species found in the reservoir (Table 1); however, only a small num-ber of specimens was collected for some of the 45 species, which impedes the calculation of valid weight-length parame-ters and the caudal fin index for all species. Where weight-length parameters were unavailable for the calculation of W∞, standard values of b = 3 and a = 0.01 were used (unfilled in Table 1).

The wolf ﬁsh, Hoplias aimara, was the species with the highest values for asymptotic and maximum lengths (105 and 100 cm, respectively), maximum and asymptotic weights (13 969.0 and 15 200.0 g, respectively), and longevity (Long= 24.97 years), as well as the smallest values of k (0.12 year1), QB (0.65), and M (0.32 year1).

At the opposite extreme, Chaetobranchus ﬂavescens had the shortest Lmax (11.6 cm) and Astyanax bimaculatus the

shortest L_∞ (13.33 cm), as well as the highest coeﬃcient of natural mortality (M= 1.57 year1) and lowest growth per-formance (Φ = 2.03), while Moenkhausia chrysargyrea pre-sented the lowest weights (Wmax= 17.00 g and

W_∞= 18.54 g). The highest von Bertalanﬀy growth constant was recorded for Hemiodus unimaculatus (k= 0.65 year1) and the highest QB was obtained for Bivibranchia notata (51.01). In general, the species presented allometric growth (b< 3.0), and most (66%) are medium-sized, with a maxi-mum length of<40 cm (Table 1).

The piscivores were the most diverse trophic category, with 15 species, followed by the omnivores (14 species), detriti-vores (10 spp.), carnidetriti-vores (4 spp.), and herbidetriti-vores (2 spp.). The highest trophic levels were recorded for Hoplias macr-ophtalmus (TL = 3.47), H. aimara (TL = 3.45), and Cichla ocellaris (TL= 3.40), while the herbivores and detritivores occupied the lowest levels, with scores of 2 (Table 1).

The ﬁrst axis of the PCO explains the vast majority (92.6%) of the variation in the data, while the second axis explains only 3.3%. The parameters Wmax (r= 0.99), Woo

(r= 0.98); Lmax (r= 0.98), longevity (r = 0.94), and Loo

(r= 0.89) were all strongly correlated with the first axis, but negatively with the growth constant, k (r= 0.86) and natural mortality (r= 0.79). The results of the PCO permit the dif-ferentiation of the fish community by trophic category, due to the differences in both the life history strategies of the spe-cies and their population parameters (Fig. 2).

The piscivorous species presented greater asymptotic body lengths than the omnivores (Fig. 3a), but did not differ from the detritivores, which were, in turn, statistically similar to the omnivores (F= 4.99; P = 0.012; Tukey test: P < 0.05). The piscivores presented the lowest values for von Berta-lanffy’s growth constant in comparison with the omnivores and detritivores (F= 6.628; P = 0.003; Fig. 3b). However, the Ar values did not vary significantly among trophic cate-gories (F= 2.3; P = 0.12; Fig. 3c).

The regression between the consumption/biomass ratio (QB) and the asymptotic length (Fig. 3d) was signiﬁcant (P< 0.05) for the three trophic categories: omnivores: Y = 0.07996 9 X + 13.84, R2_{= 0.4; piscivores: Y = 0.1134 9}

X+ 14.77, R2= 0.76, and detritivores: Y = 1.218 9 X + 65.44, R2_{= 0.54. The slope for the detritivores is signiﬁcantly}

diﬀerent from those of the piscivores (F= 17.90; P = 0.000) and omnivores (F= 18.80; P = 0.000), although the

Fig. 2. Ordination of ﬁrst PCO (Principal Coordinates Analysis) axes for population parameters of ﬁsh species (see Table 1), Coaracy Nunes reservoir, based on trophic guild

(a)

(c)

(b)

(d)

Fig. 3. a) Asymptotic length (cm), b) von Bertalanffy’s growth constant (k), c) Aspect Ratio (Ar) of the caudal fin and d) Consumption/Biomass ratio (QB)9 Asymptotic Length for three trophic categories of fish species, Coaracy Nunes reservoir. Bars with same letter (A, B) not different statistically (P> 0.05), *significant regressions (P< 0.05)

(5)

piscivores and omnivores were similar to one another (F= 0.71; P = 0.400).

Discussion

Estimates of population parameters are important for the understanding of the general biological characteristics of fish species, in particular those targeted by commercial fisheries (Nikolsky, 1969; Gulland, 1988; Freitas et al., 2014). In addi-tion, correlations between parameters permit the comparative analysis of demographic and biological data for species from different regions (Pauly, 1998).

Length parameters (Lmax and L∞) are inﬂuenced by

genetic, environmental (availability of resources), and popu-lation (density) factors, whereas growth rates (k) are deter-mined genetically and/or physiologically (Beverton and Holt, 1957; Sparre and Venema, 1992). As expected, the popula-tion parameters were closely related to one another, but pres-ent marked distinctions when the species are grouped according to their trophic specializations, reﬂecting the parti-tioning of habitats by the diﬀerent species.

While the majority of species are members of the pisci-vore guild, which is a characteristic of other reservoirs (Araujo-Lima et al., 1995; Agostinho et al., 2007), the pop-ulation parameters recorded in the present study indicate that the detritivorous species have adapted better to the local conditions than other groups, given that they have similar body lengths to the largest piscivores, but higher growth rates, which are similar to those of the omnivores. The advantages for detritivorous species in Brazilian reser-voirs are related to the abundance of resources derived from the drowning of the biomass of the terrestrial vegeta-tion during the initial ﬂooding (Castro and Arcifa, 1987), a process that continues through the regular operational ﬂuc-tuations in the level of the reservoir, permitting the growth of terrestrial vegetation along the margins during low water, which is submerged during the subsequent high water per-iod, contributing to the production of detritus (Agostinho et al., 1997).

The detritivores also present higher consumption (QB) ratios in comparison to the other guilds, irrespective of the size of the species, which is probably due to the fact that detritus is diﬃcult to metabolize, requiring speciﬁc groups of bacteria in the gut to liberate the energy for its consumers (Cebrian, 2002). The metabolism of the bacteria that permit the digestion of the detritus is dependent on high tempera-tures, a characteristic of the reservoirs located in tropical ecosystems, characterized by poorly oxygenated lentic waters, which tend to provide the warmer environment favored by these species.

Most of the ﬁsh species analyzed in the present study can be classiﬁed as having r-type life history strategies, character-ized by high rates of growth and mortality, and small body size (Sparre and Venema, 1992), combined with reduced lon-gevity (short life cycle), given that the maximum age reached by a species tends to be inversely related to its growth and mortality rates. These characteristics are typical of species adapted for life in reservoir environments (Luiz et al., 2005), and r-strategist species tend to form the base of the food

chain, given their predominance in the lowest trophic levels (Gubiani et al., 2012).

The population parameters recorded in the present study reflect the existence of a fish fauna at the study site with a diversity of habits and life histories, but with a predominance of short-lived, opportunist species. The values recorded for the different indices are consistent with those found for the same species or genera in other habitats (Angelini and Agost-inho, 2005; Isaac et al., 2008; Gubiani et al., 2012; Freitas et al., 2014), and may provide the basis for trophic web models, such as Ecopath, that are still relatively scarce for reservoir environments (but see Angelini et al., 2006; Gubi-ani et al., 2011).

Ackowledgements

This study is part of Julio C. Sa-Oliveira’s Ph.D dissertation in the Graduate Program in Ecology at the Federal Univer-sity of Para in Belem, Brazil, under the supervision of V. J. Isaac-Nahum. We are also grateful to Central Eletricas do Norte (ELETRONORTE) for logistical support and CNPq for scholarships.

References

Agostinho, A. A.; Hahn, N. S.; Gomes, L. C.; Bini, L. M., 1997: Estrutura troﬁca. In: A planıcie de inundacß~ao do alto rio Pa-rana: aspectos fısicos, biologicos e socioecon^omicos. A. E. A. M. Vazzoler, A. A. Agostinho and N. S. Hahn (Eds). Eduem, Maringa -PR, pp. 229–248. (In Portuguese).

Agostinho, A. A.; Gomes, L. C.; Pelicice, F. M., 2007: Ecologia e Manejo de Recursos Pesqueiros em Reservatorios do Brasil. 1a. edn. Eduem, 501 pp. (In Portuguese).

ANA, 2011: Ag^encia Nacional de Aguas. Available at: www.ana. gov.br (accessed on 20 August 2012).

Angelini, R.; Agostinho, A. A., 2005: Parameter estimates for ﬁshes of the Upper Parana River Floodplain and Itaipu Reservoir (Brazil). Naga, ICLARM Q, 28, 53–57.

Angelini, R.; Gomes, L. C., 2008: O artes~ao dos ecossistemas: construindo modelos com dados. Eduem, Maringa -PR, 173 pp. (In Portuguese).

Angelini, R.; Agostinho, A. A.; Gomes, L. C., 2006: Modeling energy ﬂow in a large neotropical reservoir: a tool to evaluate ﬁshing and stability. Neotrop. Ichthyol. 4, 253–260.

Angelini, R.; Moraes, R. J.; Catella, A. C.; Resende, E. K.; Librala-to, S., 2013: Aquatic food webs of the oxbow lakes in the Pant-anal: a new site for ﬁsheries guaranteed by alternated control? Ecol. Model. 253, 82–96.

Araujo-Lima, C. A. R. M.; Agostinho, A. A.; Fabre, N. N., 1995: Trophic aspects of ﬁsh communities in Brazilian rivers and res-ervoirs. In: Limnology in Brazil. J. G. Tundisi, C. E. M. Bicudo and T. Matsumura Tundisi (Orgs.). Brazilian Academy of Sci-ences/Brazilian Limnological Society, Rio de Janeiro, pp. 105– 136.

Beverton, R. J. H.; Holt, S. J., 1957: A review of the lifespans and mortality rates of ﬁsh in nature, and their relation to growth and other physiological characteristics. In: The lifespan of ani-mals. Vol. V. G. E. Wohstenholme and M. O’Conner (Eds). Churchill, London, pp. 142_–180.

Bezerra, P. E.; Cunha, B. C. C.; Del’Arco, J. O.; Drago, V. A.; Montalv~ao, R. M. G.; Eulalio, H. N. J. J.; Prado, P.; Amaral-Filho, Z. P.; Novaes, A. S.; Vieira, P. C.; Fraga, A. Y. C.; Costa, J. R. S.; Salgado, L. M. G.; Braz~ao, J. E. M., 1990: Pro-jeto de zoneamento de recursos naturais da Amaz^onia Legal. IBGE/Departamento de Recursos Naturais e Estudos Ambient-ais, Rio de Janeiro, 212 pp. (In Portuguese).

(6)

Binohlan, C.; Pauly, D., 2000: The population growth table. In: Fishbase 2000: concepts, design and data sources. R. Froese and D. Pauly (Eds). ICLARM, Los Ba~nos, Laguna, pp. 138–145. Castro, R. M. C.; Arcifa, M. S., 1987: Comunidades de peixes de

reservatorios no sul do Brasil. Rev. Bras. Biol. 47, 493–500. Cebrian, J., 2002: Variability and control of carbon consumption,

export, and accumulation in marine communities. Limnol. Ocea-nogr. 47, 11–22.

Christensen, V.; Pauly, D., 1992: ECOPATH II– a software for bal-ancing steady-state ecosystem models and calculating network characteristics. Ecol. Model. 61, 169–185.

Clarke, K. R.; Gorley, R. N., 2006: Primer v6: user manual and Tutorial. Primer-E, Plymouth, 190 pp.

FAO-ICLARM, 1996: Stock assessment tools. User’s manual. Ed: FAO-ICLARM, Rome.

Freitas, T. M. S.; Prudente, B. S.; Fontoura, N. F.; Montag, L. F. A., 2014: Length-weight relationships of dominant ﬁsh species from Caxiuan~a National Forest, Eastern Amazon, Brazil. J. Appl. Ichthyol. 30, 1081–1083.

Froese, R.; Binohlan, C., 2000: Empirical relationships to estimate asymptotic length, length at ﬁrst maturity, and length at maxi-mum yield per recruit in ﬁshes, with a simple method to evalu-ate length frequency data. J. Fish Biol. 56, 758_–773.

Froese, R.; Pauly, D. (Eds), 2011: FishBase. World Wide Web elec-tronic publication. Available at: http://www.ﬁshbase.org. (accessed 23 November 2013).

Gayanilo, F. C., Jr; Pauly, D., 1997: FAO-ICLARM stock assess-ment tools (FiSAT) – Reference manual. FAO Computerized Information Series (Fisheries). No. 8. FAO, Rome, 262 pp. Gubiani, E. A.; Angelini, R.; Gomes, L. C.; Agostinho, A. A., 2011:

Trophic models in neotropical reservoirs: testing hypotheses on the relationship between aging and maturity. Ecol. Model. 222, 3838–3848.

Gubiani, E. A.; Gomes, L. C.; Agostinho, A. A., 2012: Estimates of population parameters and consumption/biomass ratio for ﬁshes in reservoirs, Parana State, Brazil. Neotrop. Ichthyol. 10, 177– 188.

Gulland, J. A., 1988: Fish population dynamics. John Wiley & Sons, New York, 372 pp.

IBGE, 2010: Instituto Brasileiro de Geograﬁa e Estatıstica. Available at: www.ibge.gov.br (accessed on 25 July 2012).

Isaac, V. J.; Selva, C. O.; Ruffino, M. L., 2008: The artisanal fishery fleet of the lower Amazon. Fish. Manag. Ecol. 15, 179–187. Luiz, E. A.; Petry, A. C.; Pavanelli, C. S.; Julio, H. F., Jr; Latini, J.

D.; Domingues, V. M., 2005: As assembleias de peixes de reser-vatorios hidreletricos do Estado do Parana e bacias limıtrofes. In: Biocenoses em reservatorios: padr~oes espaciais e temporais. L. Rodrigues, S. M. Thomaz, A. A. Agostinho and L. C. Go-mes (Eds). RiMa, S~ao Carlos, pp. 169–184. (In Portuguese). Nikolsky, G. V., 1969: Theory of ﬁsh population dynamics. Oliver &

Boyd, Edinburgh, 323 pp.

Palomares, M. L. D.; Pauly, D., 1998: Predicting food consumption of ﬁsh populations as functions of mortality, food type, morphomet-rics, temperature and salinity. Mar. Freshw. Res. 49, 447–453. Pauly, D., 1980: On the interrelationships between natural mortality,

growth parameters and mean environmental temperature in 175 ﬁsh stocks. J. Cons. Internat. I’Explor. Mer 39, 175_–192. Pauly, D., 1998: Tropical ﬁshes: patterns and propensities. J. Fish

Biol. 53, 1–17.

Pauly, D.; David, N., 1981: ELEFAN I, a BASIC program for the objective extraction of growth parameters from length-frequency data. Ber. der Deut. Wiss. Komm. f€ur Meer. 28, 205–211. Pauly, D.; Munro, J. L., 1984: Once more on the comparison of

growth in ﬁsh and invertebrates. Fishbyte 2, 21.

Sa-Oliveira, J. C.; Angelini, R.; Isaac-Nahum, V. J., 2014: Diet and niche breadth and overlap in fish communities within the area affected by an Amazonian reservoir (Amapa, Brazil). An. Acad. Bras. Ciênc. 86, 111–126.

Sparre, P.; Venema, S. C., 1992: Introduction to tropical fish stock assessment, Part 1. FAO fisheries technical paper. Introduction to tropical fish stock assessment. FAO, Rome, 376 pp.

Taylor, C. C., 1958: Cod growth and temperature. J. Conseil 23, 366_–370.

Vazzoler, A. E. A. M., 1996: Biologia da reproducß~ao de peixes tele-osteos: teoria e pratica. Eduem, Maringa, 169 pp.

Author’s address: Ronaldo Angelini, Departamento de Engenharia Civil, Universidade Federal do Rio Grande do Norte, UFRN, BR-101, Campus Universitario, 59078-970 Natal, Brazil.