Life history characteristics and production of Ceriodaphnia silvestrii Daday (Crustacea, ) under different experimental conditions. SANTOS1 , M.A.P.F. dos, MELÃO1, M.G.G. & LOMBARDI2 , A.T.

1 Departamentos de Hidrobiologia e 2 Botânica – Universidade Federal de São Carlos P.O. Box.676, 13565-905 – São Carlos, SP – Brazil e-mail 1 [email protected]; [email protected]; [email protected]

ABSTRACT Life history characteristics and production of Ceriodaphnia silvestrii Daday (Crustacea, Cladocera) under different experimental conditions. Effects of different food sources and culture medium on life history traits of Ceriodaphnia silvestrii were studied under controlled conditions. were submitted to five different treatments: (1) autoclaved natural water filtered through plankton net of 20mm mesh size, supplied with Chlorella lacustris as food source; (2) autoclaved natural water filtered through plankton net of 20 mm mesh size, supplied with Scenedesmus bijugus; (3) soft reconstituted water supplied with S. bijugus; (4) soft reconstituted water supplied with S. bijugus plus humic substances (20 mg L-1) and (5) hard reconstituted water supplied with S. bijugus. Observations were performed at 12 hours intervals from organism birth until its natural death. All treatments were kept at 25 ± 1ºC. Results showed longer longevity in treatment 1 and better fecundity on treatment 2. In treatment 3 (with artificial culture medium), fecundity and growing parameters were lower than in natural water treatment (3). Increasing in water hardness did not result in better suitability of reconstituted water to C. silvestrii. The addition of humic substances resulted in greater fecundity and survival values. Body length-dry weight relationship was established: W = 11.3 x L2.52 (R2=0.91). Secondary production was calculated, for each treatment, based on estimated biomasses increment and egg production. Treatment 2 showed the higher production (1.3 mg DW. female-1.day-1). Through the present study, it was possible to conclude that: S. bijugus is a relatively better food source for C. silvestrii than C. lacustris; the addition of humic substances in artificial culture medium resulted in better reproduction and development of C. silvestrii; natural water proved to be a better culture medium for C. silvestrii than artificial reconstituted water; and increase in reconstituted water hardness (recommended by EPA) did not result in a more suitable culture medium to tested animals. Keywords: Ceriodaphnia silvestrii; Life history; reproduction, secondary production, humic substances, length-dry weight relationship.

RESUMO: Características bionômicas e produção de Ceriodaphnia silvestrii Daday (Crustacea, Cladocera) sob diferentes condições experimentais. Foram estudados os efeitos de cinco diferentes trata- mentos nas características bionômicas de Ceriodaphnia silvestrii : (1) água do ambiente natural autoclavada e filtrada através de rede de plâncton (20mm) com fornecimento de Chlorella lacustris como alimento; (2) água do ambiente natural filtrada e autoclavada através de rede de plâncton (20mm) com fornecimento de Scenedesmus bijugus; (3) água reconstituída mole com fornecimento de Scenedesmus bijugus; (4) água reconstituída mole com fornecimento de S. bijugus mais substâncias húmicas (20mg L-1) e (5) água reconstituída dura com fornecimento de S. bijugus. Características de crescimento e re- produção foram observadas a cada 12 horas desde o nascimento dos organismos até o momento de sua morte natural. A temperatura de cultivo para todos os tratamentos foi de 25±1 ºC. Os resultados evidenciaram maior longevidade no tratamento 1 e maior fecundidade no tratamento 2. No tratamento 3 (meio de cultivo artificial), os valores dos parâmetros fecundidade e crescimento foram menores que no tratamento com água natural (tratamen- to 2). O aumento na dureza da água não afetou o crescimento e a reprodução de C. silvestrii. A adição de substâncias húmicas resultou em valores maiores de fecundidade e de sobre- vivência. A relação peso-comprimento estabelecida para C. silvestrii foi W = 11.3 x L2.52 (R2=0.91). A produção secundária foi calculada para cada tratamento a partir de estimativas do incremento em biomassa e da produção de ovos. O tratamento 2 apresentou a maior taxa média de produção total (1,3 mgPS.fêmea-1.dia-1). O presente estudo permite concluir

Acta Limnol. Bras., 18(2):199-212, 2006 199 que: S. bijugus é um alimento de maior qualidade para C. silvestrii que C. lacustris; a presença de substâncias húmicas no meio artificial produziu uma melhora nos parâmetros de reprodução e desenvolvimento; a água do ambiente natural mostrou ser mais adequa- da que o meio de cultivo artificial; e que um aumento na dureza total não tornou o meio de cultivo artificial (recomendado pela EPA) mais adequado para o cultivo de C. silvestrii. Palavras-chave: Ceriodaphnia silvestrii, historia de vida, reprodução, produção secundária, substâncias húmicas, relação peso seco-comprimento.

Introduction pointed out life history strategies evolved by species of different sizes to avoid two Zooplankton plays an important role in main kinds of predators: invertebrates and trophic chains of aquatic ecosystems, vertebrates. Certain large species (e.g. large significantly contributing to matter and Daphnia) are able to grow to a size at which energy flux from the primary producers to they are relatively invulnerable to the top consumers (Abrantes & Gonçalves, invertebrate predators. The juveniles of 2003). Cladoceran zooplankters particularly, these species maximize energy input into as efficient filter-feeders, take a relevant growth and postpone reproduction until they part on this flux. As generalist herbivores, have attained a certain size. This strategy these animals do not feed only on algae, is of little value to the small-sized species but also on bacteria, organic detritus and that remain vulnerable to invertebrates dissolved organic matter (Arnold, 1971; throughout their lives. Instead, small species Sarnelle, 1986; Vijverberg, 1989; Ojala et al., minimize the impact of invertebrate 1995; Boersma & Vijverberg, 1996; Abrantes predation by initiating reproduction at earlier & Gonçalves, 2003). For these reasons, it stages. Following the onset of reproduction is of great interest to study mechanisms they continue to grow, and thereby reduce affecting its population dynamics and predation by invertebrates. energy allocation strategies. Food quality and/or quantity can alter Some of the most important life history strategies of cladoceran species, environmental factors controlling leading to a greater vulnerability of some zooplankton growing and reproduction are size classes to predators (Lynch, 1980; temperature, food quantity and quality, and Schwartz & Ballinger, 1980). This flexible the physical environment suitability reproductive pattern may be an adaptation (Vijverberg, 1989; Fonseca, 1998). Effects to a variable environment imposed by of these factors are well known in the fluctuations of dominant algal species literature. Temperature is responsible for presenting different food quality decreasing development time, instar characteristics. intervals, time between clutches and For cladocerans, it can be observed that longevity (Bottrell, 1975; Hardy & Duncan, results due to culture medium variations, 1994; Amarasinghe et al., 1997; Rietzler, like water hardness, (Lewis ; Maki, 1981; 1998). Vanni & Lampert (1992) verified that Girling & Garforth, 1989 ; Abrantes & Gon- Daphnia galeata reacts similarly to resource çalves, 2003) are very similar to those depression, regardless if it results from low obtained from food quality variations food quantity or low food quality. (Schwartz & Ballinger, 1980 ; Vanni & The observed effects of relatively lower Lampert, 1992). quality and quantity of food on cladoceran C. silvestrii, a common neotropical species generally are delayed age and cladoceran species, occurs in natural decreased size at maturity, smaller environments which frequently have an production of eggs and neonates (Hall, 1964; expressive amount of dissolved organic Boersma & Vijverberg, 1996; Díaz-Castro & matter (DOM). Gouvêa (2004) reported Hardy, 1998; Rose et al., 2000; Abrantes & approximately 10mgC.L-1. The importance of Gonçalves, 2003), and also reduced biomass DOM on zooplankton diet is also emphasized production (Melão, 1997; Melão & Rocha, in Salonen & Hammar (1986), which may 2001) Ryther (1954) described toxicity and consist of a significant source of energy inhibitory effects of Chlorella species on for filter feeders as cladocerans. filtering rates, survival, growth and However, there is little information reproduction of Daphnia magna. about environmental factors’ influence on In a classic study dealing with life history traits of C. silvestrii. Fonseca cladoceran life histories, Lynch (1980) (1991) studied life history traits of C. silvestrii

200 SANTOS, M.A.P.F. dos et al. Life history characteristics and production of ... at laboratory cultures, regarding some C. silvestrii neonates were harvested selected growing and reproduction from females cultured in laboratory parameters. Rietzler (1998) evaluated controlled conditions. As soon as they were temperature effects on development time, born, each neonate was measured by a reproduction and survival of C. silvestrii micrometer eyepiece, fitted to a Leica MZ6 reared in natural water fed on natural seston. optical microscope, and individually placed Moreover, this tropical cladoceran in test tubes vessels, containing 50 mL of species is recently standardized for the tested medium. The animals were ecotoxicological bioassays by Brazilian maintained at a temperature of 25 ± 1 ºC, in pollution monitoring institutions, CETESB, a 12-h/12-h light/dark cycle. Algae were intending to substitute foreign species such supplied in a concentration of 105 cells mL-1. as Daphnia similis and Daily, the medium was replaced by a fresh in ecotoxicological studies (ABNT, 2005). one, containing fresh food. The animals The purpose of this study is to were observed every 12 hours since its birth investigate the effects of variations on until natural death, except for the treatment culture medium (natural or reconstituted with humic substances, which was carried water and different water hardness), food out for a period of 15 days. Stock cultures quality (two algae species as food source), of C. silvestrii were previously acclimated and the presence of natural DOM, as humic for a month to each experimental condition substances, (in an equivalent concentration (temperature, food concentration, tested found in natural environments) on some life culture medium). history traits of C. silvestrii, such as Growing and reproduction parameters development times, age and size at first of C. silvestrii were daily recorded during reproduction, clutch size, fecundity, the time of experiment, and were defined longevity, medium and maximum body size. based on Vijverberg (1989) and Bottrell It was also obtained the body length-dry (1975). Life history parameters were: body weight relationship of C. silvestrii, which length, age at primipara, size at primipara, allows, together with life history information, number of instars, instar of primipara, estimate female biomass and secondary longevity, number of eggs per female, production (growth and reproduction) in the number of neonates per female, percentage different experimental conditions. of eclosion, embryonic period and time between clutches. Materials and methods Animals were submitted to five different treatments (Tab. I). Natural water, used in Natural water and animals, which treatments 1 and 2, was previously initiated stock cultures, were collected at autoclaved and filtered through plankton net Barra Bonita reservoir (22º 29´ S and 48º 34´ W, of 20 mm mesh size. For treatment 4, it was Barra Bonita, São Paulo state, Brazil). used IHSS Suwannee River Humic Algal species used as cladocerans food Substances (7.0% ash, 52.47% C, 4.19% H, source in this study (Scenedesmus bijugus 42.69% O, 1.10% N, 0.65% S, and 0.02% P). and Chlorella lacustris) were cultured in WC Artificial medium used was medium (Guillard & Lorenzen, 1972), reconstituted soft fresh water (U.S. EPA, -1 modified by Lombardi & Vieira (2000). Algal 2002), with hardness of 44.0 mg CaCO3 L cultures were maintained in laboratory (treatments 3 and 4, and in stock cultures) controlled conditions, under a 12-h/12-h light/ and hard water, with hardness of 150.0 mg -1 dark cycle and at 25 ± 1ºC. CaCO3 L (treatment 5).

Table I: Experimental conditions of the five tested treatments on C. silvestrii culturing.

Treatment Culture medium Algae Hardness Humic subst. Replicates

1 natural C. lacustris soft - 12 2 natural S. bijugus soft - 15 3 reconstituted S. bijugus soft - 17 4 reconstituted S. bijugus soft 20mg L-1 9

5 reconstituted S. bijugus hard - 16

Acta Limnol. Bras., 18(2):199-212, 2006 201 Differences among the five treatments production was estimated following were analysed with one-way ANOVA concepts and methods described by followed by the Tukey multiple comparison Edmondson & Winberg (1971), Winberg (1971) test when parameters were parametric and and Downing & Rigler (1984). Total with Kruskal-Wallis (non-parametric ANOVA) production (P) of the experimental followed by Dunn´s multiple comparison test population was calculated by summing when they were not (Zar, 1999). production related to growth (Pg) and that To establish body length-dry weight related to reproduction (Pr). Pg is the indivi- relationship for C. silvestrii, 20-40 non- dual biomass increment during the experi- preserved individuals of similar sizes from mental period, while Pr was obtained by stock cultures (kept in similar conditions to multiplying the number of eggs produced treatment 2) were harvested, measured by by each female during the experiment by a micrometer eyepiece fitted to a Leica MZ6 microscope, and placed inside aluminum each egg weight (0,21mg). Individual growth vials, previously dried (60ºC for 24 hours), production (Pg) was calculated for each treatment using mean initial (M ) and final and weighed on a Mettler Toledo UMT2 0 microbalance (accuracy of 0.1 mg). Three size (Mt) individual biomass after t days, as shown classes were chosen: neonates up to 24 below: -1 hours of age, juveniles and adult females Pg = (Ln Mt – Ln M0) t (without eggs). There were at least three replicates for each size class. This method Results is similar to those described in Bottrell et al. (1976) and Mansudire (1994). Development, growing and repro- Mean dry weights and body length duction parameters of C. silvestrii were measurements were used to obtain the significantly affected by the five different length dry-weight relationship, as follows: treatments (as shown in Tab. II). b W = a.L , where Animals reared in treatment 2 W is dry weight (mg), L is body length produced neonates before any other (mean (mm), ´a´ and ´b´ are constants. Regression of 2.63 days), followed by treatment 4 (2.89 equation was derived using Origin 6.0TM days), treatment 3 (3.09 days), treatment 5 software. biomasses of each (3.21 days) and treatment 1 (4.21 days) (Tab. III). treatment were estimated, based on length- Treatment 2 showed the highest value dry weight relationship obtained by the for mean values of neonates per female method described above. Secondary (see Fig. 1). During all life cycle, females of

Table II: Statistical analysis of selected life-history parameters of C. silvestrii at five different treatments. Different letters (a, b, c and d) indicate statistically significant differences. Parameter Test applied (**) P Treatment 1 2 3 4 5

Age at primipara (days) KW / D < 0.0001 c b a ab a Size at primipara (mm) KW / D < 0.0001 ab cd bcd bcd a Instar of primipara KW / D < 0.0001 ab b a a a Total number of instars KW / D < 0.0001 b b a a a Longevity (days) KW / D < 0.0001 b b a nd* a

Number of eggs / female KW / D < 0.0001 b b a c a Number of neonates / female KW / D < 0.0001 b b a c a Embryonic period (days) A / TK < 0.0001 b ab d b bc Time between clutches (days) A / TK < 0.0001 b b a b b

Body length (mm) KW / D < 0.0001 b b a c a

Secondary production (P)*** A / TK < 0.0001 bc a d c d

Growth production (Pg)*** A / TK < 0.0001 a b c b c

Reproductive production (Pr)*** A / TK < 0.0001 b a c b c (*) nd: not determined up to the end of experiment; (**) A = Anova, KW = Kruskal-Wallis; TK = Tukey- Kramer; D = Dunn´s. (***) mg DW.female-1’.day-1

202 SANTOS, M.A.P.F. dos et al. Life history characteristics and production of ... this treatment produced the highest mean Fig. 3 illustrates the influence of the number of neonates, 107.07 (Tab. III). The five tested treatments on proportion of lowest mean number of neonates per female aborted eggs by females of C. silvestrii. was verified in treatment 3, with just 7.41 Females submitted to treatments 3 and 4 neonates. Treatments 1 and 2 showed the had faster increasing of proportion of highest values for eclosion percentage, aborted eggs early in their lives. Females which were very similar (89.30% and 85.65%, from treatments 1 and 2 had a similar lower respectively). Treatment 5 had an eclosion of proportion up to old age, when just before 78.06%, followed by treatment 4, with 74.42%, senescence and death they had an and treatment 3, with 52.92% (Tab. III). increasing of aborted eggs. The increasing Food source did not result in in hardness postponed high proportion of statistically significant differences, on time aborted eggs. between clutches, among treatments 1 and 2: 1.64 and 1.66 days, respectively (Tab. III). Treatment 1 was responsible for the Among all treatments, treatment 3 showed greatest survival and treatment 3 for the a slightly longer time (1.90 days). lowest one (see Fig. 4). Mean body lengths Fig. 2 illustrates the influence of per instar are given in Fig. 5. Animals of environmental conditions on fecundity treatment 2 showed the greatest body length parameters, such as accumulated number and the fastest growth. Animals reared in of neonates per female. Treatment 2 treatment 1 grew slower, and showed the showed higher values of neonates per greatest mean longevity (36.0 days), followed female, followed by treatment 1. by those of treatment 2 (28.8 days) (Tab. III).

Figure 1: Mean fecundity per female per instar of C. silvestrii from five different treatments: 1-5.

Figure 2: Accumulated number of neonates female-1 in relation to instars of individuals of C. silvestrii submitted to five different treatments: 1-5.

Acta Limnol. Bras., 18(2):199-212, 2006 203 -1 .day -1’ g DW.female m obtained by other authors C. silvestrii development, growing, reproduction parameters and production estimates found in life history experiments, from five different treatments (1-5). The last four columns present data from C. silvestrii

* Mean number of neonates produced per female instar. Data marked with “-” were not registered by the authors. ** T able III:

204 SANTOS, M.A.P.F. dos et al. Life history characteristics and production of ... Figure 3: Proportion of aborted eggs (%) in relation to instar of females of C. silvestrii submitted to five different treatments: 1-5.

Figure 4: Survival (%) of individuals of C. silvestrii submitted to five different treatments: 1-5.

Figure 5: Mean body length (mm) per instar of Ceriodaphnia silvestrii submitted to five different treatments: 1-5. The error bars give the S.D.

Acta Limnol. Bras., 18(2):199-212, 2006 205 The maximum mean body length was measurements for other size classes are registered in treatment 2 (1.02 mm), while also given in Tab. IV. The length-dry weight the minimum in treatments 3 and 5 (0.74 and regression equation and plots of dry weight 0.75 mm, respectively) (Tab. III). Mean number against body length can be seen in Fig. 6. of molts of these two treatments showed Through the obtained length-dry similar values: 23.0 for the first one, and 18.3 weight relationship (Fig. 6), it was possible for the second one. to estimate the biomass of animals Adult females of C. silvestrii, used to submitted to each treatment, in each ins- length-dry weight relationship determination, tar, throughout its life (Fig. 7). It was also varied in mean body length from 0.719 to possible to estimate the secondary 0.753 mm and in mean individual dry weight production (P), constituted by both from 4.81 to 5.85 mg. The ranges of similar production related to growth (Pg) and

Table IV: Data used for determination of length-dry weight relationship for C. silvestrii: mean body length (mm) and mean individual dry weight (mg), from three life stages (neonate, juvenile and adult). Mean body Mean indiv. N* Length (mm) Weight (µg) Neonates 3(120) 0.341 ± 0.006 1.337 ± 0.169 Juveniles 3(60) 0.561 ± 0.013 2.113 ± 0.159 Adults 5(100) 0.736 ± 0.017 5.335 ± 0.523 * Number of replicates. In parenthesis, total number of individuals measured.

Figure 6: Relationship between body length (mm) and dry weight (mg) of C. silvestrii.

Figure 7: Biomass of animals submitted to the five different treatments (1-5), estimated based on the obtained length-dry weight relationship.

206 SANTOS, M.A.P.F. dos et al. Life history characteristics and production of ... reproduction (Pr) (Tab. II and III). Results of Treatment 2 had the greatest secondary accumulated production also clearly show production value (1.30 mg DW female-1 .day-1), the effects on females submitted to the five followed by treatment 4 (0.90), treatment 1 (0.81), treatments (Fig. 8). treatment 5 (0.52) and treatment 3 (0.50).

Figure 8: Secondary production of females submitted to all treatments (1-5). P = Total secondary production, Pg = Growth production, and Pr = Reproductive Production (µg DW.female-1.instar-1). Discussion neonates from the brood chamber; molting In all treatments of the present work, accompanied by an increase in body size; in the same way as described by Bottrell and release of a new set of eggs from the (1975) for eight cladoceran species, adult ovaries into the brood chamber. Moreover, females of C. silvestrii passed through the the duration of adult instars was very simi- following cycle of events: development of lar to time between clutches and embryonic eggs and release of fully developed period.

Acta Limnol. Bras., 18(2):199-212, 2006 207 Effects of humic substances food, some parameters showed significant The addition of humic substances in differences. Females fed on S. bijugus reconstituted water (treatment 4) resulted (treatment 2) had its first reproduction at in higher values of reproduction and earlier age and earlier instar, and showed a survivorship, such as neonates per clutch greater primipara size (Tab. III). Fecundity (Fig. 1), survival (Fig. 4), time between parameters were affected by food quality, clutches, embryonic period, mean longevity, although statistical analysis did not show number of eggs and neonates per female significant differences. Although the during all its life, percentage of eclosion, relation Pg/Pr was similar (0.40 and 0.43), and body length (Tab. II and III), in differences on P, Pg and Pr values of comparison with treatment 3. Other treatments 1 and 2 were statistically parameters such as age at first reproduction, significant (Tab. II). size at primipara, instar of primipara, and It is well established that some species total number of instars, showed statistically of Chlorella can liberate toxins in the water, similar values. The addition of humic thus altering growth and reproduction of substances also shifted the relation Pg/Pr cladocerans (Ryther, 1954; McMahon & Rigler, from 1.5 in treatment 3 to 0.75 in treatment 1965; Infante & Litt, 1985). Greater longevity 4, thus showing an inversion on energy and lower fecundity are some of the allocation strategy (Tab. III). Females reared responses in reaction to the presence of in treatment 3 showed the most toxic substances in the water (Vijverberg, accentuated curve of aborted eggs (Fig. 3), 1989). Results of treatment 1 in comparison which was slightly attenuated by the with treatment 2 suggest a possible toxic presence of humic substances (treatment 4). effect. The relatively high quality of The addition of DOM was sufficient to Scenedesmus bijugus permitted animals to obtain better growing and reproduction have more eggs per clutch, more neonates results for C. silvestrii, since it can also be per clutch, greater body length, earlier utilized as food source for cladocerans primipara and a greater size at first (Arnold, 1971; Vijverberg, 1989; Boersma & reproduction (as shown in Tab. III). Lower Vijverberg, 1996). This result could also be longevity is adopted in favor of a greater explained by an addition of nutrients (7.0% reproduction when organisms are fed on ash present in humic substances samples) high quality food (Vijverberg, 1989). Other in the synthetic medium (Girling & Garforth, authors obtained similar results when 1989). Salonen & Hammar (1986) feeding cladoceran species with Chlorella. demonstrated the importance of DOM in the Lundstedt & Brett (1991) concluded that nutrition of zooplankton in highly humic Scenedesmus acutus is a higher quality lakes, frequently found in tropical and food than Chlorella homosphaera to subtropical regions. They showed that Daphnia longispina, Bosmina longispina and several cladocerans species are able to uti- Chydorus sphaericus. Infante & Litt (1985) lize allochthonous organic matter as food obtained poor growth and reproduction source, either directly or via other organisms culturing Daphnia pulicaria and Daphnia (e.g., bacteria). They obtained good growth thorata with Chlorella sp. These results and reproduction results for planktonic were attributed to inhibitory effects and in the absence of decreasing of filtering rates caused by photosynthetic production. Although Chlorella toxins (Ryther, 1954; McMahon & allochthonous DOM is generally considered Rigler, 1965; Infante & Litt, 1985). refractory or of little value as energy source, Two patterns of reproduction became it is composed of numerous molecules. apparent in treatments 1 and 2. In the first Since the concentration of allochthonous one, reproductive maturity was delayed and DOM is very high in some lakes, even a brood size was smaller, but a longer small biologically available proportion may longevity was observed. On the other hand, be quantitatively important as a source of early maturity with high fecundity and carbon for food webs, either directly or shorter longevity were observed in animals indirectly. fed on S. bijugus. Thus, C. silvestrii, in a rich environment, would be able to take advantage of high quality sources available. Effects of food quality In a less favorable environment (lower Considering treatments 1 and 2, whose quality food), C. silvestrii may not reproduce difference was only the algae supplied as at the same rate, but its life is lengthened

208 SANTOS, M.A.P.F. dos et al. Life history characteristics and production of ... perhaps due to decreased reproductive had lower mean body length and grew more stress. Similar results were found by slowly. Moreover, animals delayed to reach Schwartz & Ballinger (1980) for Daphnia the first reproduction and showed the pulex fed on Pediastrum duplex (relatively smallest size at first reproduction. Girling & high quality) and Melosira ambigua Garforth (1989) tested the influence on (relatively low quality), and by Vanni & variations in culture medium on the survival Lampert (1992) to Daphnia galeata fed on and reproduction of Daphnia magna. These Scenedesmus acutus (relatively high quality) authors compared EPA reconstituted water and Oocystis lacustris (relatively low quality). with filtered river water for D. magna during Females reared in treatment 2 showed 28 days. They registered a greater number low proportion of aborted eggs until its of neonates per female and survival rate senescence and natural death, as well as on river water treatment. When blends of females from treatment 1 (see Fig. 3). In both waters were tested, better results for spite of a longer longevity, which delayed these two parameters were obtained in the increasing aborted eggs rate of females treatments which had the highest from treatment 1 by some instars, this percentages of natural water. Vijverberg parameter was similar for both treatments. (1989) also pointed out that artificial waters According to Vijverberg (1989), this is a prepared using distilled water can give poor typical reproductive behavior of Cladocera, culture results. which generally produce large broods up However, there are many arguments for to old age, and before senescence and the use of a synthetic medium for culture death there may be a short period with zooplankton at laboratory-controlled smaller broods and a high proportion of conditions: the most important is that a aborted eggs. Such phenomena can be synthetic medium has a known and observed also in Fig. 1. reproducible composition. This cannot be guaranteed when natural waters (surface-, Effects of culture medium spring-, well, tap-water) are used for Culture medium comparisons zooplankton culturing. Each laboratory has produced the most pronounced differences its own natural water, which further on both growing and reproduction complicates the interpretation of results. parameters of C. silvestrii submitted to Moreover, a synthetic medium is more treatments 2 and 3 (Tab. III). All parameters certainly free from pesticides, pollutants and showed statistically significant differences DOM than most of natural waters, which can (Tab. II): females of treatment 2 reproduced be undesirable to the purposes of at an early age and instar, had a greater zooplankton cultures. size at primipara and mean body length, had greater longevity, production of eggs Effects of hardness and neonates per female, eclosion The increasing in water hardness percentage, number of instars, and had produced statistically significant differences lower time between clutches and embryonic on size at primipara (0.66 mm and 0.56 mm), period in comparison to females of embryonic period (1.73 d and 1.54 d) and treatment 3. Females reared in treatment 3 time between clutches (1.90 d and 1.65 d) showed the most accentuated curve of for females of C. silvestrii submitted to aborted eggs (Fig. 3), when compared with treatments 3 and 5, respectively (see Tab. II treatment 2 curve. Secondary production and Tab. III). All other observed parameters values also indicate these pronounced did not show significant differences, such differences. as all secondary production values (Tab. II). The major differences revealed in this Increases in water hardness, as an study were between treatments 2 and 3. attempt to improve the suitability of artifici- Even after acclimation period, reconstituted al culture medium did not result in water was less adequate to culturing this significant differences on growth and cladoceran species in experimental reproduction parameters (Tab. II) between conditions, in spite of hardness adjustment. treatments 3 and 5. Fonseca (1998) observed Abrantes & Gonçalves (2003) found similar better survival and fecundity of C. silvestrii -1 results when culturing Ceriodaphnia reared in soft water (4.0 mg CaCO3 L ) than -1 pulchella both in natural and synthetic in hard water (143.0 mg CaCO3 L ). Fonseca medium. C. pulchella reared in ASTM hard & Rocha (2004), culturing C. silvestrii on -1 water fed on Selenastrum capricornutum natural hard water (143.0 mg CaCO3 L ),

Acta Limnol. Bras., 18(2):199-212, 2006 209 obtained higher values for fecundity and of results of the present study with other similar values for body growth. authors, which also investigated life history Treatments tested in the present study of C. silvestrii under controlled conditions. suggest that greater water hardness did Rietzler (1998) studied life histories not result in better reproduction and responses of C. silvestrii under the following growth of C. silvestrii reared in laboratory conditions: water from the natural habitat cultures, nor in an improvement of the of the tested organisms (Barra Bonita suitability of U.S. EPA (2002) reconstituted Reservoir, São Paulo State, Brazil), fed on water to this cladoceran species. natural seston, at 25ºC. Water hardness and pH were not considered by this author. Biomass and Secondary Production C. silvestrii fed on natural seston had its Length-dry weight regression equation primipara at later instars, were smaller at was in agreement with other studies first reproduction, had smaller body length, (Dumont et al., 1975; Bottrell et al., 1976; and production of eggs and neonates per Persson and Ekbohm, 1980; Vijverberg, female than in natural water treatments 1989). As expected, b constant varied near (1 and 2) of the present study. 3.00 (2.52 in this study), indicating that body Fonseca (1991) cultured C. silvestrii in weight increases exponentially with length. natural water (pH ~7.0, water hardness of ~150.0 mg CaCO L-1), fed on Monoraphidium Dumont et al. (1975) reported similar results 3 5 -1 for Ceriodaphnia quadrangula (W = 1.7 x L2.26) dybowskii (10 cells mL ), at 25ºC. Females and Ceriodaphnia reticulata (W = 5.91 x L2.02), submitted to this culture condition had and Maia-Barbosa & Bozelli (2005) for greater fecundity, size at primipara and body Bosmina hagmanni (W = 11.93 x L2.68) and length when compared to Rietzler (1998) Ceriodaphnia cornuta (W = 4.23 x L1.89). The data. Fonseca (1991) growth and longevity separation of individuals in size classes for data were similar to data from treatment 2 further weighting was a good method for of the present study, except that fecundity length-dry weight determination, since size parameter was lower (85 neonates per is closely related to the age of animals, and female against 107 neonates per female in animals of similar sizes present similar treatment 2). Abrantes & Gonçalves (2003), weights. Moreover, the same equation fitted studying Ceriodaphnia pulchella, also well to all treatments, as demonstrated by demonstrated that food conditions altered the agreement between secondary all these life history parameters, as can be production values (which were calculated seen in Tab. III, comparing results of based on such equation results) and the treatments 1 and 2 from the present study obtained life history parameters. with Rietzler (1998) data. Secondary production values clearly show the amount of energy allocated by Conclusion C. silvestrii between growth and reproduction, among the different Through the present study, it was environmental conditions tested in the possible to conclude that S. bijugus is a present study. It was clear that animals relatively better food source for C. silvestrii reared in good food and medium conditions than C. lacustris in laboratory cultures, based allocated a greater amount of energy on on the observed life history parameters. The reproduction, while when they were in a relatively higher quality food provided earlier poor environment, energy was primarily primipara, a greater size at primipara, and a allocated in surviving and maintenance shorter longevity, while the relatively lower (Tab. III). Duncan (1989) describes the same quality food resulted in longer longevity, behavior, when studying planktonic rotifers later primipara, and a smaller size at maturity. and cladocerans. The present results are It was also verified that the addition of in accordance with life history strategies humic substances in artificial reconstituted described by Lynch (1980) for large-sized water resulted in better development, cladoceran species: when in good growing, reproduction and survival values environmental conditions, they initially for C. silvestrii. Natural water proved to be invest a greater amount of energy in growth better culture water for C. silvestrii than ar- and, after reaching maturity, they allocate tificial reconstituted water, as shown by the nearly all of their energy to reproduction life history parameters. Increasing water (Fig. 8, treatments 1 and 2). hardness did not improve U.S. EPA Finally, Tab. III also shows a comparison reconstituted water for C. silvestrii.

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