Effect of Salt Addition and Feeding Frequency on Cascudo Preto Rhinelepis Aspera

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Effect of salt addition and feeding frequency on cascudo preto Rhinelepis aspera(Pisces: Loricariidae) larviculture

By R. K. Luz1 and J. C. E. dos Santos2

1Laboratorio de Aquacultura da Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil; 2Estacao deHidrobiologia e Piscicultura de Tres Marias-CODEVASF, Tres Marias, Minas Gerais, Brazil

Introduction

The cascudo preto Rhinelepis aspera is a detritivorous fish

species that occurs in the Sao Francisco River (Sato et al.,

1998) and the Parana River (Agostinho et al., 1995). Thisneotropical freshwater fish is important for reservoir fisheries

and river ecology. It also has aquaculture potential, in

particular for the international ornamental aquarium industry.

However, little is known about effective larviculture of this

species.

Fish larval rearing is considered to be a difficult stage for

many species (Santos and Luz, 2009). Determining the best

feeding frequency is important to achieve better growth and

survival (Rabe and Brown, 2000), and to optimize laboratory

culture procedures (Luz and Portella, 2005). One potential

management option during larviculture can be the addition of

salt to the culture water for improvement in survival and or

growth of some freshwater neotropical species (Beux and

Zaniboni-Filho, 2007; Luz and Santos, 2008; Santos and Luz,

2009). Thus, rearing in different salinities during some days of

the culture then returning to freshwater at later stages is

important because the environment into which the juveniles

will be released for production or for stocking of reservoirs will

be freshwater.

The aim of this study was to evaluate the effect of low level

salt additions to the rearing water during the first 7 days of

exogenous feeding and, subsequently, determine the effect of

the return to freshwater for seven more days, using two

different feeding frequencies on growth and survival of

R. aspera.

Materials and methods

The experiment was conducted at the Hydrobiology and

Hatchery Station of Tres Marias, Minas Gerais, Brazil. Larvae

were reared under largely controlled conditions in 24 circular

aquaria (2-L volume; white color; constant aeration; photo-

period 10L:14D). The light level at the water surface was

150 lux. Each day at 09.00 h, temperature and dissolved

oxygen were determined in all aquaria using the YSI 55

equipment. Dissolved oxygen was 5.0 0.9 mg L)1 and the

average temperature was 26.0 0.8C. Artemia nauplii were

offered as food (daily prey concentrations = 400, 600 and

800 Artemia larvae)1, from 1 to 5, 6 to 10, and 11 to 14 days of

feeding, respectively). These levels were divided in accordance

to the feeding frequency. Aquaria were siphoned daily to

remove waste and about 50% total volume was renewed with

water from prepared stock solutions.

First-feeding larvae ofR. aspera (age 5 days; total length

= 6.23 0.32 mm; weight = 3.22 0.11 mg, n = 20) weretransferred directly from freshwater to various salinities:

S0 = freshwater (control); S2= 2 g salt L)1; S4 = 4 g

salt L)1; andS6= 6 g salt L)1. The larvae were reared under

these conditions during the first 7 days of feeding. For each

salinity, two feeding frequencies were used: F2= twice a day (at

08.00 and 17.00 h), and F4 = 4 times a day (at 08.00, 11.00,

14.00 and 17.00 h). Stocking density was 10 larvae L)1 (20 lar-

vae aquaria)1). The work was conducted with a 4 2 factorial

design (four salinities, two feeding frequencies, and three

replicates each).

The test media of freshwater and three salinities used in the

experiments were prepared and stocked in 500-L containers.

Commercial salt was used to prepare the solutions (Remo

Brazilian Industry). The pH values of the stock solutions were7.15, 7.19, 7.21 and 7.27, and the respective conductivity values

(lS cm)1) were 60, 3780, 6540, 9480 in freshwater, and 2, 4 and

6 g salt L)1, respectively (measured on the HORIBA U10

equipment).

After the first 7 days of feeding in different salinities and the

control, all larvae were counted to determine survival; samples

(n = 35) of larvae from each aquarium were fixed in formalin

10% to measure total length (mm) with an electronic caliper

(Starret), and individual weights (mg) to 0.0001 g precision.

To continue larval rearing, the larvae of all treatments were

transferred directly to freshwater and subsequently reared in

the freshwater for 7 days. For the transfer, fish were captured

with a 0.5 mm diameter mesh. After a complete waterexchange, fish were returned to the same aquaria. Due to

some mortality and larvae samples taken for measurement,

the stocking density was adjusted to reach 7 larvae L)1

(14 larvae aquaria)1). At the end, after 7 days in freshwater

(14 days of feeding), all animals were collected to determine

the survival and growth (weight and total length) as describe

above.

The specific growth rate (SGR) of larvae was determined

[SGR = 100 (lnWtf) ln Wti) Dt)1, with Dtthe time interval

(in days) between Wti (initial weight) and Wtf(final weight)].

Survival and growth data were compared by parametric

Factorial ANOVAANOVA, and means were compared using Tukey s test

at a 5% probability level using the SATISTICASATISTICA 7.0 program

(Statsoft INC., 2004).

J. Appl. Ichthyol. 26 (2010), 453455

Published 2010.

This article is a US Government work and is in the public domain in the USA.

ISSN 01758659

Received: November 1, 2008

Accepted: August 28, 2009

doi:10.1111/j.1439-0426.2009.01371.x

U.S. Copyright Clearance Centre Code Statement:01758659/2010/26030453$15.00/0

Applied IchthyologyJournal of


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Results

Table 1 shows the growth and survival of R. aspera after

7 days of initial feeding at different salinity regimes and in

freshwater (control). Weight, SGR and survival were similar

among all treatments, without pronounced effects from salinity

(S), feeding frequency (F) or interaction between S F. Total

length, however, was significantly influenced by salinity

(P < 0.01) and feeding frequency (P < 0.05). The twice daily

feeding frequency showed better length growth than the four

times daily feeding regime, while rearing at a salinity of

6 g salt L)1 resulted in lower growth (as expressed by total

length) compared to the other salt treatments.Table 2 shows the growth and survival ofR. aspera reared

in freshwater after being returned from exposure to different

salt concentrations. Rearing for an additional 7 days resulted

in survival rates, weight, and SGR similar to control, and were

not significantly influenced by the initial exposure to various

salt concentrations (Si) or feeding frequency (F). There also

was no Si Finteraction effect. In contrast, total length was

significantly affected by the initial exposure to salt concentra-

tions. The worst effects (P < 0.05) were registered in speci-

mens exposed to the treatment S60.

Discussion

Five-day-oldR. aspera larvae can be transferred directly from

freshwater to water containing salt (up to 6 g salt L)1) and

reared under these conditions for the first 7 days of feeding.

After this period the animals can be returned to freshwater.

These osmotic changes do not affect survival. Low salinities,

up to 4 g salt L)1, have been demonstrated as allowing for

good survival when rearing freshwater larvae (Luz and

Portella, 2002; Beux and Zaniboni-Filho, 2007; Luz and

Santos, 2008; Santos and Luz, 2009). However, those studies

did not evaluate the effects of returning the test animals from

different salinities to freshwater. This tolerance to different

salinities during the larvae initial development suggests the

presence of mechanisms and structures related to the acclima-

tion process to osmotic variations. This is an important pointthat can be used in the prevention of diseases and to improve

juvenile production. The addition of salt (up to 4 g salt L)1)

can help reduce infestations in Rhamdia quelen ofIchthyoph-

thirius multifiliis (Garcia et al., 2007), a common parasite in

freshwater larviculture and which often causes high mortality.

Similar growth rates in freshwater and different salt

concentrations were verified in R. aspera larvae, except for

total length. This indicates that the species presents good

acclimation and tolerance capacity to salt concentration

exposures up to 6 g salt L)1. However, the reduced total

length registered in the fish reared at higher salinities is not well

understood. Future works need to elucidate fully the treatment

effects on the total length ofR. aspera larvae.

After transfer of the test specimens from the different saltconcentration exposures to freshwater, the weight gain and

Table 1Total length, weight, specific growthrate (SGR), and survival of Rhinelepisaspera larvae reared for first 7 days offeeding in different salt concentrationsand feeding frequencies

Total length (mm) Weight (mg) SGR (% mg day)1) Survival (%)

Means for Feeding Frequency (F)F2 13.4 1.4

a 33.6 4.5 33.5 2.0 88.7 7.4F4 12.6 1.2

b 27.7 8.3 30.3 4.4 85.9 11.5Means for Salinity (S)

S0 14.2 0.9a 31.9 6.9 35.5 3.2 92.5 9.3

S2 13.3 1.3a 30.8 8.4 31.8 4.4 86.6 10.8

S4 13.3 0.4

a

34.7 5.4 33.9 2.2 86.0 6.5S6 11.4 0.8b 26.5 6.5 29.8 4.0 84.2 10.7

Statistical F valuesFeeding frequency (F) 5.16* 3.91ns 4.44ns 0.13ns

Salt concentration (S) 10.82** 1.93ns 1.74ns 0.91ns

Interaction (F S) 1.16ns 1.86ns 1.37ns 0.20ns

Means followed by same superscript letters did not differ in Tukeys test (P < 0.05); *(P < 0.05);**(P < 0.01); ns(not significant). F2 = twice a day, and F4 = 4 times a day feeding frequency.S0 = freshwater; S2 = 2 g salt L

)1; S4 = 4 g salt L)1; and S6 = 6 g salt L

)1.

Table 2Total length, weight, specific growthrate (SGR), and survival of Rhinelepisaspera larvae during 7 days of feeding

in freshwater, after transfer from ini-tial rearing in different salt concentra-tions

Total length (mm) Weight (mg) SGR (% mg day)1) Survival (%)

Means for feeding frequency (F)

F2 21.1 1.0 121.7 14.9 18.4 2.5 97.0 7.1F4 20.9 0.7 117.6 20.4 20.0 4.4 95.2 10.1Means for initial salt concentrations (Si)

S00 21.8 0.5a 125.7 14.2 19.2 3.4 94.3 7.8

S20 21.4 0.7a 126.3 25.9 20.4 4.9 95.2 11.6

S40 20.5 0.4ab 119.0 9.9 17.6 2.6 95.7 9.6

S60 20.1 0.6b 107.6 5.8 18.9 2.3 100.0

Statistical F valuesFeeding frequency (F) 0.43ns 0.36ns 0.56ns 0.06ns

Initial saltconcentration (Si)

6.81* 1.04ns 0.59ns 0.50ns

Interaction (F Si) 0.32ns 0.11ns 0.85ns 0.66ns

Means followed by same superscript letters did not differ in Tukeys test (P < 0.05); *(P < 0.05);**(P < 0.01); ns(not significant).F2 = 2 times a day, and F4 = 4 times a day feeding frequency. S00,S20,S40, andS60initial salt concentrations used in first 7 days of feeding; final rearing in freshwater(more than 7 days of feeding).

454 R. K. Luz and J. C. E. dos Santos


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SGR in freshwater were similar to the controls, confirming

acclimation capacity to short-term osmotic changes. However,

the lower total length in the S60 treatment was simply a

consequence of the lower initial total length result from the

first 7 days of exposure to high salt concentrations.

The feeding frequency did not affect R. aspera larval

survival, weight gain or SGR during rearing in different salt

concentrations; however, total length was reduced when larvaewere offered food rations four times per day. After transfer

from different salinities to freshwater, the larvae can continue

being fed twice a day. Feeding frequency between twice and

four times a day also did not affected survival and growth of

Hoplias lacerdae (Luz and Portella, 2005), or walking catfish

Clarias macrocephalus(Petkam and Moodie, 2001) larvae. For

these species, twice daily feeding frequencies optimize labor for

other larviculture activities. However, feeding frequencies have

different results in different species (Cho et al., 2003; Kikuchi

et al., 2006; Mohseni et al., 2006). Different feeding frequen-

cies must still be tested for R. aspera juveniles and adults to

determine optimum management regimes for rearing.

Acknowledgements

This research received support from CODEVASF CEMIG,

Brazil and FAPEMIG (Fundacao de Amparo a` Pesquisa do

Estado de Minas Gerais, Brazil). We thank Dr Yoshimi Sato

for assistance and support during this work.

References

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Authors address: Jose C. E. dos Santos, Estacao de Hidrobiologiae Piscicultura de Tres Marias-CODEVASF, CEP.39205-000, Tres Marias, Minas Gerais, Brazil.E-mail: [email protected]

Management ofR. aspera larviculture 455

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Effect of Salt Addition and Feeding Frequency on Cascudo Preto Rhinelepis Aspera