28

One of the best proven ways to prevent

pathologies is to create immunity in the

animal. With more than 200 years to

back up their efficacy, vaccines have

helped to prevent and in some cases

eliminate many disorders in humans,

farm animals and family pets.

Regarding aquaculture, the evolution has

been a bit slower. If we look at fish, the

first vaccine for salmonids was licensed

in the US in 1976. Since then, the use of

immunoprophylaxis in fish has expanded

to other places and species.

In the case of penaeid shrimp things are

a bit more complicated. Unlike more

complex vertebrates, whose immune

systems depend heavily on adaptive,

antigen-specific responses such as anti-

bodies and T cell receptors, invertebrate

defenses use generic, innate immunity.

Therefore, they lack any form of immu-

nological memory similar to that found in

jawed vertebrates. Vaccinating inverte-

brates, such as shrimp, should conse-

quently be an ineffective management

strategy resulting in no more than short-

lived, non-specific immune stimulation.

The shrimp innate defense system con-

sists of cellular and humoral components

working in coordination for the detec-

tion/elimination of pathogens potentially

hazardous to the host. In both cases

hemocytes play an important role. In

cellular defense hemocytes are responsi-

ble for phagocytosis, encapsulation and

nodule formation. On the other hand,

humoral response consists on the activa-

tion and release of molecules stored

within hemocytes, such as anticoagulant

proteins, agglutinins, phenoloxidase en-

zymes, antimicrobial peptides, pattern

recognition proteins, lectins, toll recep-

AQUAFEED::ADVANCES IN PROCESSING & FORMULATION from Aquafeed.com Vol. 7 Issue 3

Feeding shrimp

FOCUS

By Àlvaro Ortiz, Product Manager, Norel

One of the biggest problems related to intensification in

animal production has been disease. Farm animals suffer

from a great variety of infectious diseases that have been

traditionally controlled by the use of pharmaceuticals. But as

zootechnology has advanced, prevention has gained more

importance, moving from a reactive to a preventive strategy.

Modulation of penaeid

shrimp immune

system as a strategy

to control disease

Ph

oto

by

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rtes

y o

f C

SIR

O

29

tors, protease inhibitors, etc.

The first organ involved in crustacean

immune system is the cuticle, it works as

the first physical barrier, and it contains

antimicrobial substances.

If the pathogens cross the outer defense,

hemocytes participate in the inactivation

of invading organisms, and regulate

different physiological functions i.e., exo-

skeleton hardening, cuticle damage heal-

ing, coagulation, carbohydrate metabo-

lism, and protein/amino acid transporta-

tion and storage.

Three different types of hemocytes are

present in the shrimp: hyaline, semi-

granular, and granular.

Hyalinocytes (5-15% of circulating hemo-

cytes or CE) are small non-refractive

cells, with a small nucleus relative to

their cytoplasm, which have few or no

cytoplasmic granules. The primary role of

these cells is related to clotting and phag-

ocytosis.

Granulocytes (10-20% of CE) have the

smallest nucleus and a high number of

cytoplasmic granules. Granulocytes dis-

play phagocytic activity and store en-

zymes as prophenoloxidase (proPo), lyso-

zyme, phosphatase, esterase, phospho-

lipase, peroxidase, protease, etc. These

cells may be stimulated by glucans, pepti-

doglycans and lipopolysaccharides to

provoke exocytosis and enzyme release.

Activation of the proPo system results in

the production of melanin, a dark-brown

pigment responsible (among other pro-

cesses) for inactivating foreign particles,

and preventing their spread

throughout the host body, as well

as for healing cuticle damages.

Semi-granulocytes (75% CE) have a

large numbers of small granules

similar to vertebrate granulocytes.

These cells posses β-1,3-glucans

receptors and their principal func-

tion involves phagocytosis, encap-

sulation and clotting.

The modulation of the shrimp im-

munology is a key element in establishing

strategies for the control of diseases in

shrimp aquaculture.

Several different methods exist to evalu-

ate the immune system status such as

hemolymph protein concentration, total

hemocyte counts, phenoloxidase activity,

free radical production, phagocytic activi-

ty, etc.

Many different additives exist in the mar-

ket claiming to have an immunostimulant

effect.

In the FAO Fisheries and Aquaculture

Report No. 1053, probiotics were recom-

mended as a tool in the control of

AHPNS, a devastating penaeid disease

causing massive mortalities of cultivated

shrimp all over the globe.

Probiotics are known to have a positive

impact on vertebrates’ immune system.

To elucidate, if the use of a commercial

probiotic ECOBIOL AQUA® (Bacillus amy-

loliquefaciens CECT 5940) a study was

conducted by the Federal University of

Rio Grande, Brazil.

The study was conducted in 12 tanks of

1,000 L, in a greenhouse at the Estação

Marinha de Aquacultura (Aquaculture

research Center), belonging to the Feder-

al University of Rio Grande (FURG), in the

town of Rio Grande-RS-Brazil.

Liptopenaeus vannamei shrimp juveniles

(2 g) were used. The tanks were pre-

pared with biofloc from other shrimp

farms, with a density of 300 individuals

per m3. Shrimp were randomly distribut-

ed to four different treatments, with

AQUAFEED::ADVANCES IN PROCESSING & FORMULATION from Aquafeed.com Vol. 7 Issue 3

“ Many different additives exist in

the market claiming to have an

immunostimulant effect. In the FAO

Fisheries and Aquaculture Report

No. 1053, probiotics were

recommended as a tool in the

control of AHPNS ...”

Fig1: Light microscopy of hemocytes from spiny lobster, Panulirus argus:

Hyalinocytes (H), semigranulocytes (SG), and granulocytes (G). Scale bar=10µm

(C. Li, J.D. Shields / Journal of Invertebrate Pathology 94 (2007) 48–55)

30

AQUAFEED::ADVANCES IN PROCESSING & FORMULATION from Aquafeed.com Vol. 7 Issue 3

three replicates each, the probiotic was

applied directly to water. The probiotic

dose varied in each treatment: 0, 20, 40

and 80 g in 1,000 L of water per week (CO,

TA, TB and TC). The probiotic application

was performed daily.

Significant differences among treatments

were found in all immune system indica-

tors.

Total protein in hemolymph (TPC) was

higher in probiotic treated shrimp. Also

granulocyte percentage (HG) was higher in

ECOBIOL AQUA® treated animals.

Additionally, apoptosis index, a way to

evaluate infection, was higher in the con-

trol group.

Results:

The proteins present in the hemolymph,

are the mechanism by which the immune

system identifies shrimp pathogens, these

in addition to identify the type of patho-

gen, can regulate the binding of patho-

gens to hemocytes, thereby controlling its

phagocytic capacity. Therefore a higher

TPC is related to a higher capacity to de-

tect and control pathogens. The higher

granulocyte percentage also indicates a

better prepared immune system as these

are responsible for phagocytic and pro-

phenoloxidase activity.

In conclusion, the addition of ECOBIOL

AQUA® helped shrimp’s immune system

to be better prepared to fight a potential

infection. These results are consistent

with other effects observed in fish (Tilapia)

as an increased number of intraepithelial

lymphocytes or higher concentration of

lysozyme in blood.

AFΩ

More information

Àlvaro Ortiz, Product Manager,

Norel

E: info@norel.net

CONTROL TA TB TC P

TPC (mg/ml) 104 ± 7a 128 ± 4b 128 ± 4 b 124 ± 6 b <0.05

HG (%) 51 ± 7a 79 ± 5 b 81 ± 5 b 67 ± 5 b <0.05

Apoptotic cells/5µl 3 ± 1a 1 ± 1b 1 ± 1 b 2 ± 1 b

<0.05