Animal Science Department, University of São Paulo, Brazil
Submission: April 04, 2018; Published: August 02, 2018
*Correspondence author: Machado-Neto R, Animal Science Department, Luiz de Queiroz College of Agriculture, University of São Paulo, Av. Pádua Dias 11, 13418-260, Piracicaba, Brazil.
How to cite this article: R Machado-Neto, Wiolene M N, Mariana C F P, Jéssica P, Débora B M. Growth and Hematology of Juvenile Piaractus Mesopotamicus Stocked At 10 Up To 40kg/m3 For Twenty-One Days. Oceanogr Fish Open Access J. 2018; 8(2): 555733. DOI:10.19080/OFOAJ.2018.08.555733
Pacu Piaractus mesopotamicus, a freshwater fish, has great potential for intensive commercial production, showing resistance to adverse conditions, such as high stocking density. Growth performance and hematological condition were evaluated in juvenile pacu stocked at high density. Juveniles were distributed into different stocking densities: 10, 20, 30 and 40kg of fish/m3 (n=4) and fed with a commercial feed for 21 days. Growth data were collected at 0 and 21 days and blood samples every 7 days. Differences were not detected in performance of pacu under different stocking densities (P > 0.05). Feed conversion rate (3.9±0.5) and specific growth rate (4.0±0.1%/ day) were worse than normally observed at this stage of life, indicating an unsuitable condition. Hematocrit of juveniles stocked at 30 and 40kg/m3 showed higher values than ones at 10kg/m3. Thus, stocking density from 10 up to 40kg/m3 did not affect growth and hematology of pacu after 21 days. However, the low growth rates indicate that all stocking densities could have determined an adverse condition to fish. Considering the high stocking density used in the present work and the intensive management without mortality, we suggest that pacu is very resistant and a promising species for fisheries.
Keywords: Teleost; Omnivorous; Performance; Red blood cells indices
Intensive fish farming involves a great challenge for the producer, that is, the concentration of large populations of animals within confined areas that increases predisposition to bacterial and parasitic diseases [1,2]. This problem is especially critical in the early larval stages of teleost, since in this period they depend on maternal components, such as nutritional and immunological factors, for their survival. According to Falcon et al.  and Baldwin  (2010), handling, biometry, vaccination and stocking density in the intensive culture system induce changes in the physiological responses interfering with health, behavior status, adaptation and welfare of fish determining situations of constant stress. Falcon et al.  also point out that the change in temperature may be one of the main causes of losses in production due to the drop in resistance and greater susceptibility to diseases.
Stressful conditions determine the release of cortisol and the consequent depression of the immune system, making fish more susceptible to infectious diseases . The understanding of the causative factors and inhibitors of stress make possible
the development of strategies that attenuate this physiological condition.
The influence of stocking density in fish growth parameters has not had an explicit adverse trend in some fish species, showing contradictory results. While S. senegalensis exhibits satisfactory growth rate at high stocking density, survival and development were not affected in Siganus rivulatus and were compromised in Oreochromis niloticus [6-8]. Although the occurrence of chronic stress caused by high stocking densities can depress the immune system, dietary supplementation represents a valuable tool to neutralize the oxidative damages in freshwater fish [9,10]. The levels of lipids and some vitamins, such as vitamins E and C, and minerals in the diet also influence antioxidant defenses and the oxidative state of fish . The main features of pacu that endorse it as a commercial species are related to its high adaptability to rearing in ponds and fish nurseries, resistance to pathogens and low demands on water quality, resulting in a species of high rusticity . Thus, the objective of the present work was to evaluate the effects of high stocking density of 10 up to 40kg/m3 for twenty-one days in the
performance and hematological parameters of juvenile pacu.
Plastic blue cages of 40 l were placed inside tank with
continuous aeration and water recirculating system with
controlled conditions (temperature 25.4±0.2 ºC; pH 7.9±0.2,
dissolved oxygen 4.0±0.5mg l-1; dissolved ammonia:<0.05mg>
l-1), seeking to guarantee the same condition for all juveniles.
Farm-raised, feed-conditioned juvenile pacu (120.2±7.5g and
14.6±0.4cm) were randomly distributed into 16 cages with
four different stocking densities (10, 20, 30 and 40kg of fish
per m3, 4 cages per stocking density). Juveniles were handfed
to apparent satiety twice a day (08h 30 and16h 30) with
commercial diet (Agromix 3.3mm: 360g kg-1 of CP, 68g kg-1 of fat,
110g kg-1 of minerals and 35g kg-1 of fiber) for 21 days. Growth
data was collected in the beginning and end of experiment
period for performance evaluation and blood samples every 7
days (3 collections) for hematological and biochemistry analysis.
Juvenile pacu were kept, maintained and treated according
to accepted standards for the humane treatment of animals
(ESALQ/USP ethics committee).
Blood samples were collected by puncture of the caudal
vessel using syringes previously moistened with disodium
ethylenediaminetetraacetic acid (Na2EDTA) solution (3%). Red
blood cell indices (RBC) were evaluated following the procedures
described by Ranzani-Paiva et al. .
Blood aliquots were diluted (1:200) in sodium formaldehyde
solution and red cells counted in Neubauer’s chamber under
an optical microscope. The result was expressed as number of
erythrocyte μl-1. The hematocrit value was determined by the
microhematocrit procedure and expressed as a percentage
of red cells in relation to whole blood. The hemoglobin (Hb)
was determined by the hemoglobin cyanide method (HiCN), a
colorimetric endpoint reaction system and the results were
expressed as g dl-1. The red blood cell indices mean corpuscular
volume (MCV), mean corpuscular hemoglobin (MCH) and mean
corpuscular hemoglobin concentration (MCHC) were determined
according to Wintrobe  by the following calculations:
a. MCV = (Hematocrit x 10) erythrocyte-1
b. MCH (pg) = (Hemoglobin x 10) erythrocyte-1
c. MCHC (g dl-1) = (Hemoglobin x 100) hematocrit-1
Plasma glucose was determined by enzyme-colorimetric test
using glucose oxidase, which catalyzes the oxidation of glucose
into glycolic acid and hydrogen peroxide. Total protein was
determined in samples of blood collected without anticoagulant
by the biuret test.
Statistical analysis was performed using the SAS (v 9.1)
program package (SAS Institute, Cary, NC, USA). The performance
data was analyzed based on a completely randomized design,
considering different stocking densities (10, 20 30 and 40Kg/
m3) the main effects. The hematological variables were analyzed
as a repeated measure-over-time design, considering stocking
density, 10, 20, 30 and 40kg/m3 as main effects. The cage effect
was considered random, and the other effects were considered
fixed in the model. After the data was confirmed for normal
distribution with the Shapiro-Wilk test, a variance analysis was
performed using the PROC MIXED (SAS Institute Inc., 2008). If
the F value was significant, the Tukey test was used for multiple
comparisons between pairs of means at 5% of probability.
standard error mean; n.s. – non-significant, P > 0.05.
The different stocking densities did not induce differences
in growth performance of juvenile pacu (P>0.05), Table 1.
Independent of stocking density, the overall mean of RWG, FCR
and SGR were 9.6±1.8 %, 3.9±0.5 and 0.4±0.1%.
Only hematocrit value was influenced by different stocking
density (P<0.05>), Table 2. Juvenile pacu maintained at 30
and 40kg/m3 showed higher hematocrit value than juveniles
maintained at 10kg/m3. Effect of sampling time was observed
for all variable analyzed (P<0.05>), except for VCM.
SEM- standard error mean; SD – stocking density effect; ST – sampling time effect; SDxST – interaction between SD and ST. n.s. – non significant, P>0.05; * significant, P<0.05> using Tukey’s test.
Intensive culture is a cost-effective production system;
however, high stocking density can trigger chronic stress in fish,
since there is competition for food and swimming movements
are limited. Considering performance and animal health, the
ideal capacity of stocking needs to be adequately determined,
since each species presents different responses in the same
stocking density. In the present work, pacu had unaffected
growth parameters under different stocking densities. In
Siganus rivulatus, stocking density at 5kg/m3 also did not
affect growth of juveniles . In Oreochromis niloticus, in turn,
the stocking density at 13kg (m3)-1 decreased development
and survival . Bittencourt et al.  observed that stocking
densities at 5.6; 8.5; 11.36kg/m3 do not influence erythrocyte
parameters, glucose level or carcass yields of Piaractus
mesopotamicus; however, density of 5.6kg/m3 results in higher
final weight. Di Maggio et al.  suggest that densities of up
to 0.5 fish l-1 (4.70kg/m3 appear to be conducive to the culture
of juvenile Orthopristis chrysoptera. The above authors worked
with densities much lower than in the present study. Merola &
Souza  however, suggest that standing crop values of 45-
50kg/m3 might be approximating a critical level for growth of
Piaractus mesopotamicus. Sadhu et al.  in turn, observed
that fish stocked at 35m3 had significant decrease in growth and
final mean weight compared to ones stocked at 14m3. Although
parameters were not influenced by different stocking density, the
present juveniles showed FCR and SGR (3.9±0.5 and 0.4±0.1%
day-1, respectively) worse that normally observed for the species
at this stage of life and much lower than expected for the period,
indicating an unsuitable condition for juveniles. Machado-Neto
et al.  observed better rates of relative weight gain and feed
conversion (1246% and 1.2, respectively) in juvenile pacu with
initial weight of 8.5±0.7g fed twice daily for 60 days with diet
containing 320g kg-1 of crude protein and 21g MJ-1 of energy.
Bicudo et al. , in turn, observed a FCR and SGR (% day-1)
around 1.05 and 2.2, respectively, after 70 experimental days
when dietary protein requirement of pacu juveniles are met.
Tesser et al. , in turn, restricting the supply of diets to 2.5%
of biomass per day, observed in pacu juveniles (initial weight of
4.3±0.1g) a FCR and SGR (% day-1) of 0.60 and 3.53, respectively.
Considering hematological parameters, only hematocrit
value was influenced by different stocking density, with juvenile
pacu maintained at 30 and 40kg/m3 showing higher hematocrit
value than juveniles maintained at 10kg/m3. Hemoconcentration
caused by stress raises hematocrit values in several freshwater
species . The elevated hematocrit values will aid in blood
oxygenation and overcoming stress . Urbinati et al. 
evaluating loading and transport stress of juvenile matrinxã
(Brycon cephalus, Characidae) at various densities, observed
higher hematocrit values after loading the fish. The authors
suggest that higher hematocrit values after loading is due to
swelling of red blood cells.
Thus, in the present work, considering the experimental
conditions used in this work, the stocking density from 10 up to
40kg/m3 did not affect growth and hematology of juvenile pacu,
Piaractus mesopotamicus, for 21 days. However, the low growth
rates indicate that all stocking densities could have determined
an adverse condition to fish. Considering the high stocking
density used in the present work and the intensive management,
collecting blood every week, without mortality, we suggest that
P. mesopotamicus is very resistant and a promising species for
Authors are indebted to “Fundacão de Amparo à Pesquisa
do Estado de São Paulo” (São Paulo State Research Foundation
– FAPESP 2014/14937-7) and “Conselho Nacional de
Desenvolvimento Científico e Tecnológico” (Brazil National
Council of Scientific and Technological Development - CNPq), for
funding the research project yielding this publication and to Fish
Culture Section, ESALQ/USP.