Growth and survival of Rhamdia quelen

(Siluriformes, Pimelodidae) larvae exposed to

different levels of water hardness

C.R. Townsend, L.V.F. Silva, B. Baldisserotto *

Departamento de Fisiologia, Universidade Federal de Santa Maria, 97105.900 Santa Maria, RS, Brazil

Received 16 July 2001; received in revised form 11 February 2002; accepted 4 April 2002

Abstract

The response to water hardness increase varies from species to species. The purpose of this study

was to verify the survival and growth of larvae of silver catfish, Rhamdia quelen, in water with

different levels of water hardness. Larvae (2.75 mg and 5.00F 0.05 mm) were randomly allotted to

experimental units (three replicates per treatment) and kept in 44-l boxes (400 larvae/box). Larvae

were exposed to five water hardness values (30, 70, 150, 300, and 600 mg l � 1 CaCO3) at pH 8.25.

Samples of larvae were collected on days 0, 7, 14, and 21, and the length, weight, and specific

growth rate (SGR) were determined for each collection. Survival and biomass were calculated on day

21. Higher larvae growth, survival, and biomass were obtained at 30 and 70 mg l � 1 CaCO3.

Therefore, this is the recommended hardness range for growth and survival of silver catfish larvae.

D 2003 Published by Elsevier Science B.V.

Keywords: Larvae; Survival; Growth; Calcium; Water quality; Rhamdia quelen; Silver catfish

1. Introduction

Total hardness is the concentration of all divalent cations in water, and Ca2 + and Mg2 +

are the most common cations in nearly all fresh water systems. The recommended value

for water hardness for fish culture in ponds is above 20 mg l � 1 CaCO3 (Boyd, 1998;

Zweig et al., 1999), mainly because of its influence on phytoplankton growth and water

0044-8486/03/$ - see front matter D 2003 Published by Elsevier Science B.V.

PII: S0044 -8486 (02 )00168 -0

* Corresponding author. Tel.: +55-55-220-8342; fax: +55-55-220-8241.

E-mail addresses: bernardo@ccs.ufsm.br, bbaldisserotto@hotmail.com (B. Baldisserotto).

www.elsevier.com/locate/aqua-online

Aquaculture 215 (2003) 103–108

pH control. However, Ca2 + is essential for fish for several biological processes such as

bone construction, blood coagulation, and many other cellular functions (Flik et al., 1995).

The internal sources of Ca2 + (bones) in fish are not easily accessible. Therefore, plasma

Ca2 + is regulated by its ingestion with food or by branchial absorption (Flik and Verbost,

1995).

Several teleost species exposed to acidic or alkaline water showed higher survival in

hard than in soft water (Freda and McDonald, 1988; Yesaki and Iwama, 1992; Laitinen and

Karttunen, 1994; Townsend and Baldisserotto, in press). The increase of water hardness

from 40 to 440 mg l� 1 CaCO3 also improved channel catfish (Ictalurus punctatus) survival

in the presence of high nonionized ammonia levels (Tomasso et al., 1980), and levels of

300–500 mg l � 1 CaCO3 are recommended for the successful hatching of eggs and

viability of silver carp (Hypophthalmicthys molitrix) larvae (Gonzal et al., 1987). However,

sunshine bass (Morone chrysops�Morone saxatilis hybrids) and tilapia (Oreochromis

mossambicus) growth was not affected by different Ca2 + concentrations (Seals et al., 1994;

Hwang et al., 1996). Because the response to a water hardness increase seems to vary from

species to species, the aim of this study was to analyze the survival and growth of silver

catfish (Rhamdia quelen) larvae at different water hardnesses.

2. Materials and methods

Silver catfish larvae (Pimelodidae) were obtained from one induced spawning

(December) using carp pituitary extract in the fish culture sector of the Universidade

Federal de Santa Maria. All eggs from the spawning were from the same cohort (female

weighing 1.96 kg and male weighing 2.0 kg) and were incubated in Hungarian-model

hatcheries (200 l) with running water. After absorption of yolk sac (3 days), larvae were

randomly assigned to treatments at hardness of 30 (28–32), 70 (68–72), 150 (148–152),

300 (292–320), and 600 (590–620) mg l� 1 CaCO3 and pH 8.1–8.3 (three replicates

per treatment). These treatments were chosen because exposure of silver catfish finger-

lings to this water hardness range did not induce any mortality or alteration in normal

behavior (Townsend and Baldisserotto, in press). Larvae were maintained in continu-

ously aerated 40-l freshwater polyethylene boxes for 21 days. Stocking density was 400

larvae/box (10 larvae l � 1). These boxes contained a water reuse system (23F 1 jC),and photoperiod was 10-h dark/14-h light, with luminosity of 0.6 lx (measured with a

LI-COR photometer model LI-185B), since dark environments improve R. quelen

growth (Piaia et al., 1999).

Larvae were fed satiation six times a day (08:00, 10:00, 12:00, 14:00, 16:00, and

18:00 h) with fish food prepared according to Lopes et al. (2001). Fish food granule size

was 100–200 Am (first week), 200–400 Am (second week), and 400–600 Am (third

week). All feces and pellet residues were removed daily by suction, and consequently,

10% of the water in the boxes was replaced with water at previously adjusted pH and

hardness.

Samples of 20 larvae were collected from each replicate on days 0, 7, 14, and 21 after

absorption of the yolk sac, mean length, and weight were measured. Specific growth rate

(SGR) was calculated for each collection according to Jørgensen and Jobling (1993).

C.R. Townsend et al. / Aquaculture 215 (2003) 103–108104

Apparent accumulated mortality was determined by counting the dead larvae daily. This

value could not be considered the real mortality because some larvae disappeared due to

cannibalism, but could give an idea of larval mortality throughout the experiment. On day

21, all surviving larvae were collected to determine survival (%) and biomass (individual

mean weight� number of surviving larvae).

Water was previously adjusted to the desired experimental pH by the addition of

sodium hydroxide and water hardness was increased by the addition of calcium chloride

(CaCl2�2H2O). Water pH was measured with a Hanna pH meter at 8:00, 12:00, 14:00, and

18:00 h and adjusted when necessary. Total water hardness was measured according to

Adad (1982) and dissolved oxygen with a Digimed oxygen meter, model DM4. Both

parameters were analyzed once a day. The following physicochemical parameters of the

water were also analyzed according to Adad (1982), but at 3-day intervals: total alkalinity,

total ammonia, and nitrite.

All data are expressed as meanF S.E.M. Mean length, weight, G, and total biomass of

treatment groups were compared by one-way ANOVA, and means were compared by

Duncan’s multiple range test, using the SPSS statistical software (version 1986). Survival

was analyzed by the chi-square test using the SAS statistical software (version 6.8, 1993).

The minimum significance level was set at P < 0.05.

3. Results

Water hardness and pH showed minor alterations in all treatments, remaining within the

expected range throughout the experiments. Maximum total ammonia reached 0.8 mg l � 1

and nonionized ammonia 0.10 mg l� 1. Dissolved oxygen remained in the 5.0–5.5 mg

l � 1 range, while oxygen saturation was in the 60.0–76.6% range. Larvae had an initial

individual mean weight of 2.7 mg and length of 5.0F 0.05 mm.

Throughout the period of 21 days, larvae maintained at water hardness of 30 and 70 mg

l � 1 CaCO3 showed greater length than the other treatments. At the first collection (day 7),

higher weight was observed at a water hardness of 30 mg l � 1 CaCO3, but at the end of the

experiment, the highest value was obtained at a water hardness of 70 mg l� 1 CaCO3. In

the first week of the experiment, the SGR was lower in the treatments with water hardness

of 150 and 300 mg l � 1 CaCO3 than in the treatment with 30 mg l � 1 CaCO3, but later,

there was no significant effect of water hardness on this parameter (Table 1). Most larvae

died in the first days of the experiment in the treatments with higher water hardness (300

and 600 mg l� 1 CaCO3), but for larvae exposed to 150 mg l � 1 CaCO3, higher mortality

was spread throughout the first 2 weeks. Larvae submitted to 70 mg l � 1 CaCO3 also

showed higher mortality in the first week, while those maintained at 30 mg l � 1 CaCO3

presented low mortality throughout the experiment. The highest survival rate at the end of

the experiment was observed at the water hardness of 30 mg l � 1 CaCO3 (80.4F 4.1%),

followed by 70 mg l � 1 CaCO3 (62.0F 5.9%). Larvae exposed to higher water hardness

levels showed much lower survival rates: 150 mg l� 1 CaCO3—8.7F 0.9%, 300 mg l � 1

CaCO3—1.0F 0.8%, and 600 mg l� 1 CaCO3—0.3F 0.3% (P < 0.05). Highest biomass

values were observed in the treatments with water hardness of 30 and 70 mg l� 1 CaCO3

(8.7F 1.0 and 10.5F 1.8 g, respectively). The increase of water hardness to 150, 300, and

C.R. Townsend et al. / Aquaculture 215 (2003) 103–108 105

600 mg l� 1 CaCO3 reduced biomass values to significantly lower values (0.7F 0.06,

0.06F 0.04, and 0.01F 0.01 g, respectively).

4. Discussion

Dissolved oxygen levels were always above 5 mg l � 1, the minimum level suggested

by Boyd (1998). There are no studies about the minimum oxygen saturation level for this

species, and as there were no differences among treatments, this parameter probably did

not affect the results. The maximum nonionized ammonia levels observed in this experi-

ment were within the maximum range suggested for growth in I. punctatus (Tomasso,

1994). Therefore, nonionized ammonia probably also did not interfere with the results.

The apparent mortality of silver catfish larvae was higher in the first days of the

experiment at higher water hardness. This mortality may be related to the osmotic stress

induced by the increase in water hardness, which also reduced length, biomass, and

survival of silver catfish larvae. Larvae were not adapted slowly to higher hardness levels

because silver catfish fingerlings survived the increase of water hardness up to 600 mg l � 1

CaCO3 (higher levels were not tested) without any problems (Townsend and Baldisserotto,

in press). This difference in tolerance to high water hardness levels may be age-related,

since the ability to maintain Ca2 + homeostasis improves with development (Grizzle and

Table 1

Length, weight, and specific growth rate (SGR) of silver catfish larvae as a function of water hardness

Hardness Days after absorption of yolk sac

(mg l� 1 CaCO3) 7 14 21

Length (mm)

30 7.02F 0.06a 9.11F 0.03a 11.82F 0.41ab

70 6.51F 0.23a 8.32F 0.41ab 13.26F 0.24b

150 5.91F 0.14b 7.88F 0.62bc 10.00F 0.36c

300 5.63F 0.26b 7.20F 0.55c 09.72F 1.28c

600 5.02F 0.10c 7.09F 0.31c 9.66ab,*

Weight (mg)

30 5.18F 0.93a 14.25F 2.57a 29.63F 3.77a

70 3.50F 0.48b 12.71F1.96a 45.41F 4.58b

150 2.50F 0.11b 11.58F 0.95a 21.70F 2.71a

300 2.49F 0.25b 11.41F 2.54a 17.16F 2.28a

600 3.04F 0.32b 13.71F 3.06a 14.83a,*

SGR (% day� 1)

30 8.86F 2.53a 7.27F 0.05a 3.55F 1.01a

70 3.43F 2.02ab 9.16F 2.16a 6.15F 1.28a

150 � 1.11F 0.64b 10.91F 0.37a 2.96F 0.63a

300 � 1.28F 1.41b 10.54F 1.87a 3.04F 0.66a

600 1.52F 1.51ab 10.43F 2.40a 2.97a,*

Means identified by different letters in the columns were significantly different ( P< 0.05) as determined by

ANOVA and Duncan’s test for comparison of mean values.

* Treatment with survivors in only one replicate on day 21.

C.R. Townsend et al. / Aquaculture 215 (2003) 103–108106

Mauldin, 1994). Recently hatched larvae have gills and renal complexes not fully

developed, but maintain their internal concentration with chloride cells located on the

skin (Alderdice, 1988; Rombough, 1999). Twenty-six days after hatching, rainbow trout

larvae presented 75% of all chloride cells in the gills. As chloride cells in the gills are more

efficient in terms of ion exchange than those on the skin (Rombough, 1999), the

ionoregulatory capacity of fingerlings would be improved in relation to larvae, explaining

their higher survival in water with high hardness levels.

The postharvest survival of 5-week-old striped bass (M. saxatilis) fingerlings, a species

extremely sensitive to handling stress, is improved by an increase in water hardness from

8–10 to 278 mg l � 1 CaCO3 (with CaCl2). The addition of NaCl (5 g l� 1) or MgCl2instead of CaCl2 did not increase survival compared to control, showing the importance of

the presence of Ca2 + in the water for this species (Grizzle et al., 1990). However, recently

hatched larvae (9 days, still with the yolk sac) of this species showed higher survival after

handling stress in water with high NaCl concentration (5 g l � 1). In this stage, Ca2 +

concentrations of 1.2–100 mg l � 1 did not alter larval survival (Grizzle et al., 1992).

However, sunshine bass (hybrids of M. chrysops�M. saxatilis) submitted to waters with

different Ca2 + concentrations (10, 20, 30, 40, or 80 mg l� 1 CaCl2) did not show any

significant difference in weight, food conversion, condition factor, or plasma Ca2 +

concentrations under normal culture conditions (pH 6.9) (Seals et al., 1994). Also, neither

the hatching rate nor the growth of tilapia larvae was affected by exposure to waters with

22 or 90 mg l� 1 CaCO3) (Hwang et al., 1996). Therefore, it seems that the increase of

water hardness up to 70–100 mg l � 1 CaCO3 does not affect survival of teleost larvae at

neutral pH. The effect of water hardness levels higher than 100 mg l � 1 CaCO3 seems to

vary according to the species studied, since 300–500 mg l � 1 CaCO3 is recommended for

efficient hatching and high viability of silver carp eggs (Gonzal et al., 1987), but reduces

the survival of silver catfish larvae.

Liming is recommended to stabilize low water pH, because calcium carbonate increases

water buffering capacity (Boyd, 1998). For silver catfish, liming must not increase water

hardness beyond 70 mg l� 1 CaCO3, because this amount is enough to reduce the effect of

acidic and alkaline pH on fingerlings (Townsend and Baldisserotto, in press), and allows

good larval growth. Based on the present results, the best hardness range for survival and

growth of silver catfish larvae is 30–70 mg l � 1 CaCO3.

Acknowledgements

The authors wish to thank Dr. Joao Radunz Neto, from the Department of Animal

Husbandry, for suggestions during the experiments, and CNPq for granting a fellowship to

C.R. Townsend.

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