J. Inland Fish, Soc. India, 29 (I), 1997 : 37 - 42

SOIL AND WATER CHARACTERISTICS OF SHRIMP PONDS AFFECTED WlTH VIRAL DISEASE J

K. K. KRISHNANI", K. V. RAJENDRAN, K. 0. JOSEPH AND B.P. GUPTA

Central Institute of Brackishwater Aquaculture 141 Marshalls Road, Egmore, Chennai-600008, lndia

Shrimp farms in the coastal districts of Tamil Nadu viz. Chidambamar (Tuticorin) and

Ramnad were surveyed to investigate the shrimp disease outbreaks, water and soil

quality characteristics in those areas. Detailed studies revealed that the white spot

disease caused by a virus was the major cause of mortality of shrimp. Penaeus indicus.

Soil and water samples coliected from affected and unaffected ponds were characterised

for various parameters. The soil and water quality parameters of affected ponds showed

significant difference vis a vis source and unaffected ponds. The particulars pertaining

to the disease outbreak and the water and soil quality characteristics are described.

Introduction

There is adequate knowledge on good farming practices and disease prevention methods but, generally, the basic principles of shrimp culture are not being followed. Poor environmental condition bring in a state of stress which is unfavourable to the shrimp but favourable to the disease causing agents. White spot disease, has been the major cause of large scale mortalities of cultured shrimp in lndia (Anon., 1994). The widespread outbreak of disease in June-July 1995 in shrimp farms in Chidambarnar (Tuticorin) and Ramnad districts had resulted in heavy economic loss to shrimp farmers. In order to collect information regarding various biotic and abiotic factors involved in this disease outbreak, a survey has been conducted to various shrimp farms.

Material and Methods

Samples of healthy and disease affected shrimp, soil and water were collected and brought to the Institute's laboratory at Madras for detailed investigation. Tissues of healthy and moribund shrimp were fixed in Davidson's fixative and further processed using routine histological techniques (Bell and Lightner, 1988).

: Corresponding Author

Soil and water samples collected from affected and unaffected ponds (0-5 to 1 ha size) were analysed for various parameters. pH, salinity and turbidity in waters and electrical conductivity and redox potential in soils were measured using appropriate meters while, other

' water variables such as alkalinity, total suspended solids (TSS), totoal ammonia, ammonia- N, nitrite, nitrate, o-phosphate, total phosphorus, chemical oxygen demand (COD), biochemical oxygen demand (BOD) and H2S and soil conditions such as total nitrogen and organic carbon contents were determined by standard methods (Jackson, 1958 ; APHA, 1989).

Results and Discussion

On the basis of stocking density, the farms visited haye been classified into extensive (5-10 nos. / m2), semi-intensive (10-20 nos./m2) and intensive types (30-50 nos./ m2). The details regarding the farms and operational details are presented in Table-I. All the farms .are sea-based and they are either tidefed or pump-fed. It was observed that out of the 8 farms surveyed, disease outbreak was restricted to the farms which were practising semi- intensive and intensive systems. Two farms which were extensive in nature (5-10 nos/m2.) were absolutely free from the disease and shrimp attained a size of 20-25 g body weight

, Table-I : Farming practices of shrimp farms at Chidambarnar and Ramnad diseicts of Tamil Nadu

Farm~ng No. of Shrimp Stocking Dens~ty Disease Source System farms SP. nos./ m2.

1. Extenstve 1 P. monodon 5-10 Not affected Sea (Tide fed)

2. Semt intenswe 1 P. indicus 10-20 Affected Sea (pump fed)

3. Intensive 2 P. indicus 30-50 Not affected Sea

1 P. indicus 30-50 Affected Sea (Pump fed)

1: Extensive 1 P. monodon 5-1 0 Not affected Sea vide fed)

'2. Semi intensive 2 P.indicus 10-20 Affected Creek (Pump fed)

Extensive Stocked in March 1995 and were being cultured during survey .

Semi-intensivtd Intensive (Affected) Stocked in March 1995 and were being harvested during survey

Semi-intensivtd Intensive (Unaffected) Stocked in June-July 1995 and were being cultured during survey.

SOIL AND WATER CHARACTERiSTlCS OF SHRIMP PONDS 39

within 4-months. Incidently, both these farms stocked with Penaeus monodon. It has .been ieported that most species of penaeid shrimp appeared to be susceptible to the white spot disease virus (Anon., 1994). However, in the present case it was found that disease outbreak was restricted to P. Indicus. This might be due to the less stocking density in the ponds which stocked with P. monodon and /or increased resistance of large sized shrimp (P. monodon

. 20-25 g, P. indicus 3-89)

Histopathological observations

Histopathological preparations of various tissues stained with haematoxylin and eosin (H & E) showed typical manifestations of Systemic Ectodermal and Mesodermal Baculovirus (SEMBV) infection. Gill filaments showed extensive necrosis and eosinophilic intranuclear occlusions. Nuclear hypertrophy and chromatin margination were also observed. Similar observations with typical eosinophilic to basophilic occlusions in other tissues such as hemato- poeitic tissues, lymphoid organ,subcuticular epidermis, stomach and nervous tissues were also observed.

Soil characteristics

The results of the soil analysis are given in Table-2. It is evident that unaffected ponds had low -ve redox potential (-50 to -170 mV), low electrical conductivity (6.1-12.0 mmhosi

Table-2 : Soil ehara~teristics of unaffected end effected ponds d various dams at Chidarnbarnar and Ramnad

districts of Tamil Nadu

Parameter Extensive Semi-intensive1 intensive

Not affected Not affected Affected

- - - - -

cm) and low organic carbon contents (0.04-0.23 %) but in disease affected shrimp ponds at both the places, an increase in-ve redox potential (-160 to -220 mV), electr~cal conductivity (7-4-21 -8 mrnhos/cm) and organic carbon contents (0.25-0.47 %) were noted. Higher values of -ve redox potential and organic carbon contents in disease affected ponds were presumably caused by accumulation of residual feed, faecal matter, dissolved excreta and other organic matter such as dead plankton and dead prawns. Intensification of shrimp farming practices

releases large amount of organic load into the environment (Macintosh and Philips, 1992 ; Primavera, 1994 ) and this not only affects pond environment but also increases the chances of disease outbreak.

Water characteristics

The results of analyses of water samples are presented in ~a'ble-3. From this, it is evident that alkalinity values ranged from 95-111 ppm in pond waters and did not show much variation among source water, affected and unaffected pond waters. Owing to the buffering capacity of brackishwater, much variation in pH was not observed in the ponds and it varied from 7.5 to 7.9. Higher salinity was observed in affected pond waters (42-46 ppt) as compared to unaffected pond waters (37-40 ppt) and source waters (35-38 ppt).

Table-3 : Water characteristics of unaffected and affected ponds of various shrimps at Chidarnbamar and

Ramnad districts of Tamil Nadu

Parameter Source Extensive Semi-intensivellntensive

Not affected Not affected Affected

Turbidity (NTU) 2.2-18 3.2-1 2 6.2-20 11-30

Salinity (ppt) 35-38 37-38 38-40 42-46

Alkalinity (ppm) 97-1 13 104-1 1 1 95-1 10 101-108

Total Ammonia (ppm) 0.08-0.20 0.60-0.96 0.26-0.86 1.8-2.6

&phosphate (ppm) 0.004-0.008 0.008-0.009 0.006-0.01 0 0.005-0.009

Total P (ppm) 0.016-0.032 0.01 8-0.030 0.018-0.38 0.037-0.052

COD ( P P ~ ) 18-23 21 -24 19-24 22-36

' ys (rjbm) BDL BDL BDL BDL

SOIL AND WATER CHARACTEWSTICS OF SHRIMP PONDS 41

DO and COD for unaffected pond waters ranged from 3.2-5.2 pprn and 19-24 ppm, respectively. Higher values for turbidly (11-30 MU), COD (22-36 pprn), BOD (7.0-13.0 ppm), TSS (157-314 ppm), total ammonia (1.8-2.6 ppm), free ammonia (0.06-0.095 pprn), nrtrlte (0.09-0.14 pprn), nltrate (0.18-0.25 pprn), total nnrogen (2.96-3.85 ppm) and total phosphorus (0.037-0-052 ppm) and iower values for DO (1-6-4.6 ppm) were noted In waters of d~sease affected ponds. There was not much var~at~on in water quality of the sources and unaffected ponds. However, the water qualrty parameters of affected ponds showed signrfrcant drfferences vrs a vis source and unaffected ponds. H,S was not detected In all the farms surveyed. It has been noted that except TSS and DO of affected pond waters, almost all the other parameters were found to be w~thrn safe permrssrble levels (Chen and Lel, 1990 ; MEF, 1993 ; Mohan eta/. , 1995). DO, turbidity and suspended partrculate matter are factors reported to be of ~nfluence on the survival of shrimp In cutture ponds (Allan and Maguire, 1991 ; Rao, 1996 ). Reduced DO, increased nltrogen contems and excessive turbrdlty rn affected ponds mrght have resulted In severe stress to shrrrnp leadrng to disease.

It IS a well establrshed fact that the causative agent of the wrdespread outbreak of whrte spot drsease IS a virus However, on a precrse examlnatron of the outbreak In Ch~darnbarnar and the Ramnad drstncts, the affected ponds showed a marked change In the sol1 and water qualrty character~strcs. Thrs change wrth respect to the unaffected ponds may be due to the onset of drsease and further death and decay of disease shrimps and accumulation of unused feed. Thrs negat~ve change In the sort and water quality characterlst~cs clearly plays a crucral role In the severity of disease outbreaks. Hence, management practices In the affected ponds such as aeration and removal of the dead shnrnp, monitorrng and management of feedrng and removal of organic load can atleast prevent the deter~oratron of pond condrtions and thereby reduce the stress on the survrvlng anlmals. However, further study is needed to establrsh the exact nature of lnteract~on between drfferent abrotrc factors and the outbreak of drsease.

Acknowledgement

The authors are greatly beholden to Dr. K. Alagarswami, former Drrector, Central Institute of Brackishwater Aquaculture (CIBA), Chennai, for provid~ng necessary facrlit~es. They are also thankful to Dr. G. R. M. Rao, Drrector, CIBA, Chennar for keen ~nterest and encouragement.

References

Allen, G L. and Magu~re. G B., 1991 Lethal levels of low d~ssolved oxygen and effects of short term stress on subsequent growth of juven~les P monodon. AquawIture, B4 27-37.

Anon., 1994. SEMBV an emerging vrral threat to cultured shrimp In Asia Asian Shrimp News (4th quarter), 20 : 2-3.

APHA 1989 Standard methods for the examination of water and waste water 17th edn , American Public Health

Association, Washington, DC

Bell T A . and Lightner, D V , 1988 A handbook of normal shrimp histology, pp 114 World Aquaculture Soc~ety.

Baton Rouge Louisiana

Chen Jiann-Chu and Lei Shun-Chiang, 1990 Toxic~ty of ammonia and nitrite to Penaeus monodon juveniles, J

World Aquaculture Soc~efy, 21 (4) 300-306

Jackson M L 1958 Soil Chemical Analysis. Prentice Hall Englewood Cliffs, New Jersy USA

Macintosh D J and Ph~lips, M J , 1992 Env~ronmental issues in shrimp farm~ng In Sararn de H and Singh.

T (end) Proceedings of the 3rd Global Conference on the shrimp Industry Hongkong

MEF 1993 Ministry of Environment and Forests In Gazette of India - Extraordinary notlflcatlon, 19th May. 1993.

New Delh~

Mohan D Sundaramoorthy. S , and Rarnchandran S 1995 Water management and water quality control In aquous

farms pp 116-137 In Ramchandran S (ed ) Proceedrngs of National Conference on Sustainable

Aquaculture

Pr~mavera J H 1994 Env~ronmental and soclo-economic effects of shrimp farmlng the Philippines experience

Infof~sh lr~ternabonal 1194 44-94

Rao Prasada P V S V 1996 Rise and reduction of whcte spot dlseases among shrimp under culture In A P Prevention

and Cure Ffshfng Chimes, Nov 1996 pp 9-1 1