Sudden Fish Kill Associated with Bacterial Bloom in an Undrainable Fish Pond

Central Institute of Freshwater Aquaculture (CIFA)
Dhauli, Kausalyagang, Bhubaneshwar

NETWORK OF AQUACULTURE CENTRES IN ASIA
BANGKOK, THAILAND

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SUDDEN FISH KILL ASSOCIATED WITH BACTERIAL BLOOM
IN AN UNDRAINABLE FISH POND

Radheyshyam, Dilip Kumar and V.R.P. Sinha
Freshwater Aquaculture Research & Training Centre
(C.I.F.R.I)
P.O. Kausalyagang, Via Bhubaneswar, Orissa

ABSTRACT

An interesting case of fish kill in an jundrainable composite fish culture pond of 0.6 ha near Freshwater Aquaculture Research and Training Centre, Kausalyagang, Bhubaneswar due to sudden appearance of a bacterial bloom associated with a drop of dissolved oxygen to lethal levels is described. Results of on the spot bioassay test, plankton and bacterial populations, community respiration in sediment and water and chemical demand of oxygen have been presented. Possible reasons for the sudden shift in certain parameters in the ecosystem have been discussed.

INTRODUCTION

Cases of fish kills in undrainable ponds have been reported by many workers (Raghavan et al, 1977; Sharma and Mukherji, 1978; Raghavan et al, 1979; Sinha et al, 1980 and Radheyshyam, et al. MS) giving various possible causes for such mortality. Oxygen depletion caused by sudden appearance of algal bloom and planktonic swares etc. have been regarded as one of the potential factors for such cases of mass mortality which are often associated with certain imbalance in the environmental parameters. The authors have come across a case of mass mortality of carps caused by appearance of temporary bacterial bloom resulting in sudden drop of dissolved oxygen to lethal level. The present paper indicates the results of the investigation made on D.O. content, community respiration in sediment and water, chemical oxygen demand of the ecosystem and gas discharge from the sediment along with bacterial population to assess the causes of sudden drop DO. O., causing mass mortality.

MATERIALS AND METHOD

The pond is situated in Pubasasan village of Puri district about 12 km away from Bhubaneswar city near Freshwater Aquaculture Research & Training Centre in Orissa State. It is newly reclaimed pond from a very old swampy area having 0.6 ha of water spread. It maintains an average depth of 1.2 m in summer and 2.0 m in monsoon months. Pond was stocked @ 4000/ha with the fingerlings of Indian major carps - Labeo rohita, Catla catla and Cirrhinus mrigala and exotic carps - Ctenopharyngodon idella, Hypophthalmychthis molitrix and Cyprinus carpio. This was the first time when proper fish culture had been started in the pond for the last 8 months. Manuring was done with raw cow dung @ 5–6 quintals per month and fishes were fed @ 1–2% of the body weight with groundnut oil cake and rice bran.

The authors started investigations as soon as mass mortality occurred in the early morning of 4.3.1883. The following investigations were conducted:

Samples of plankton were collected by filtering 50 litres water through bolting silk No. 25 and analysed under microscope. Total bacterial load was estimated by direct count method on membrane filter after erythrosin staining (Sorokin and Overbeck, 1972). Undermentioned physico-chemical parameters were recorded. Temperature was recorded using centigrade thermometer. Water transparency was measured by inserting pin on a scale in absence of Secchi disk. Bottom sediment depth was measured with the help of wooden disk (10 cm dia.) and bamboo poles. Oxygen content was recorded with the help of battary operated Beckman's oxygen analyser.

Community respiration and chemical oxygen demand were measured from the core samples in situ by adding 1.5% neutral formalin in the water in a glass cylinder containing the intact water sediment core (Herodek and Olah, 1973). Sediment gas discharge was also measured using gas collector designed at FARTC.

Bioassay test was carried out at the pond site using 6 plastic tags filled with 10 litres of aerated and non-aerated water from the same as well as from the adjoining pond with fingerlings of rohu from nearby nursery pond.

Dead fishes were collected, examined and recorded species-wise.

OBSERVATION

Physico-chemical feature of the pond ecosystem

The pond water gradually turned from slightly greenish to deep brown within 3–4 days. Table 1 shows certain physico-chemical and biological/microbiological proportion at the time of the mass mortality of the fish.

Plankton

Planktonic concentration (more than 60 U size) was relatively poor and had the total population of 515: udm^-3. The zooplankton constituted copepods (1041 udm^-3), cladocerans (720 udm^-3) and rotifers (320 udm^-3) whereas phytoplankters comprised mixophycese (1240 udm^-3), Chlorophycead (1050 udm^-3), euglenophyceae (550 udm^-3) and bacillariophycese (230 udm^-3).

Bacterioplankton

Total bacterial load was estimated as 18.6 million cm^-3 in the bottom water and 14.2 million cm^-3 in surface mostly consisting of sulfer bacteria.

Community respiration and chemical oxygen demand

Dissolved oxygen basides being used by aquatic community for respiration it is also consumed chemically in the pond ecosystem the maximum biochemical utilisation of oxygen was 10,068 g m^-2 d^-1 in the water at the bottom of the pond. The sediment chemical O₂ demand was 7.2 g m^-2d^-1 and utilisation of O₂ in sediment community respiration was only 0.288 g m^-2d^-1. In the surface water the loss of O₂ by chemical demand was higher (5.76 g m^-2d^-1) in relation to community respiration (2.304 g m^-2d^-1). Details are summarised in the following Table II.

TABLE II

Biochemical oxygen demand in the pond ecosystem during mass mortality of carps

Bioassay test

On the spot bioassay experiment demonstrated to the farmer indicated 50–70% mortality of rohy fingerlings within 30–35 minutes in non-aerated pond water while there was no mortality up to 2 hours in aerated pond water and control pond water. The details of experimental results are given in Table III.

Fish kill record

Fishes were surfacing enmasse for gulping the air and gathering towards one side of the pond. Mortality started early in the morning and continued till forenoon. Fishes were netted out and the species-wise dead specimens were recorded. Altogether 751 fishes weighing 523 kg dies during the incident constituting silver carp, grass carp, common carp, mrigal, catla and rohu. Details are summarised in Table IV.

Examination of some of the dead specimens revealed that there was excessive mucus secretion. In some cases there was a thick mucus coat over the entire body and gills aloo. While skimming this slimy coat from the gills, some blood mixed with mucus also came out in all the species. This indicated rupture and fatal haemorrhage in the gill lamellae under acute physiological respiration distress condition (Van Duijn, 1973).

DISCUSSION

The pond had slight greenish water 3–4 days before the fish mortality started. However, the water then gradually turned to deep brown colour mainly due to the sudden appearance of the sulfer bacteria-bloom. The turbidity of the pond water (90 mg dm³, Sio₂) was not high compared to other ponds in the locality having the range of 134–140 mg dm^-3 Sio₂ (Mohanty & Rath, 1982). The temperature of the pond water ranged between 27.5–28.5°C which is within the normal limit, although high temperature has been reported to cause mass mortality in some cases, for example, Durve and Rajbansi (1975) recorded fish mortality during unprecedented drought at 35.9°C in the lake water and Radheyahyam et al, (MS) reported the mass fish kill at 37.5°C.

The D.O. value was 0.5 mg dm^-3 in surface water and 0.2 mg dm^-3 on the soil water interface during early hours of the day which indicated very low dissolved oxygen availability for the fish life. Similarly others have noted the low level of oxygen in the water during fish kill, for example Natarajan et al, (1963) at 0.2–1.8 mg dm^-3 D.O. level; Sharma and Kukerji (1978) at 0.8 mg dm^-3; Radheyehyam et al, (MS) at 0.08 mg dm^-3 and Singh (1977) at 0.08 mg dm^-3 in the water column.

Depletion of oxygen is normally known to be caused by excessive plankton population or macrophyta. However, the pond had no macrophyta nor the population of plankton was so high. The total concentration of phytoplankters was 2081 udm^-3 and that of zooplankton was 3070 udm^-3 only. In this it is interesting to note that Sharma and Kukerji (1978) recorded 1,29,584 udm^-3 blue green algae and 10385 udm^-3 zooplankton when they observed fish kill in a pond.

The biological oxygen demand normally indicates the community respiration, which showed the value of 0.288, 8,448 and 2.304 g m^-2d^-1 in the sediment, sediment water and surface water of the pond respectively during the fish kill. The microbial community respiration value was low in the pond sediment as well as in sediment water mainly because of setting of the anaerabic condition in presence of low availability of oxygen, this in turn, contributed to the production of H₂S and other obnoxious gases in the sediment.

Further, the anaerobic condition in the sediment resulted in increased chemical oxygen demand (7.2 g m^-2d^-1) there, whereas the accumulated gases (10.4 dm³m^-2) and the highly rich organic matter in the bottom mud also required quite high chemical oxygen demand (1.92 g m^-2d^-1) in sediment water interface.

Thus the total demand of biochemical oxygen was 7.488 g m^-2d^-1 in sediment, 10.368 g m^-2d^-1 in bottom water interface and 8.064 g m^-2d^-1 in the surface water of the pond which created serious drain on total of oxygen in the pond.

With such severe oxygen demand both biological as well as chemical in the pond created serious problem for fish life for available oxygen. In addition to these the production of H₂S providing the energy base for sulfer bacteria (Words & Whipple, 1918) needs special mantion. Since not much is known about the bacterial bloom in such fish culture ponds and its role in creating imbalance in oxygen level in the pond causing a fatal condition for the fish. In the present observations the bacterial concentration was as high as 14.2 million cm^-3 in surface water and 18.6 million cm^-3 at the water soil interface mostly of sulfer bacteria compared to the bacterial concentration in such rural ponds varying from 0.2–12.9 million cm^-3 as has been recorded during environmental monitoring survey programme of FARTC (Olah, 1983). Such excessive growth of sulfer bacterial in fact appearing as bloom, also needed considerable amount of oxygen.

Therefore the drain of available dissolved oxygen in community respiration particularly by the bloom of sulfer bacteria both in the sediment and the water and in chemical demand for anaerobic state of sediment and sediment water interface left little oxygen for fish life and hence the mass mortality occurred. Considering all the factors for depletion of oxygen it appears that the most dominant factor for the fish kill is the sulfer bacterial bloom.

ACKNOWLEDGEMENT

Authors wish to record their gratitude to Dr. A.V. Natarajan, Director, Central Inland Fisheries Research Institute for his interest and Dr. J. Olah, FAO Consultant on Pond Microbiology for his waluable help.

REFERENCES

Durve, V.S. and V.K. Rajhansi, 1975. Fish mortality and fishing during an unprecendented drought in lake Fishhola, Udaipur, Indian J. Fish. 22 (1 & 2) : 297–299.

Herodek, S. and J. Olah, 1973. Primary production in the frozen lake Balaton. Annal. Biol. Tihany 40 : 197–296.

Mohanty, S.K. and R.K. Rath, 1982. Report on the progress of work at Kausalyagang (Orissa). VIth Workshop on AICRP on Composite fish culture and fish seed production, FARTC (Dhauli), Kausalyagang, Orissa, 1st & 2nd July 1982; 49–62.

Natarajan, A.V., K.L. Shah and K.C. Bhau, 1962. A case for fish mortality in Kadhur pani Jano in Chilka Lake. Sci. & Cult. 29 : 97–99.

Olah, J. 1983. FAO Consultancy Report on Pond Microbiology for intensification of Freshwater Fish Culture & Training (IRD/75/031).

Radheyshyam, B.B. Satpathy and V.R.P. Sinha, (MS) Environmental diel cycle during mass fish kill and planktonic collapse in an undrainable rural fish pond.

Raghavan, S.L., P.K. Sukumaran, B.V. Govind and L. Manju, 1977. A case of fish mortality in Byramangala Reservoir. J. Inland Fish. Soc. India 9: 203–204.

Raghavan, S.L., M.P. Rahaman and B.V. Govind, 1979. Suspendoids A Factor for Fish Mortality. J. Inland Fish. Soc. India. 11(2): 111–112.

Sharas, H. and A.P. Mukerji, 1978. An examination of environmental factors for the cause of a summer fish kill, in a tank near Allahatad. Curr. Sci. 47(11) : 389–391.

Sorokin, Y.I. and H. Overbeck. 1972. Direct microscopic counting of micro organisms. P. 44–47. In: Sorokin and H. Redota (Eds.) Microbial production and decomposition in freshwater IIP Handbook 23 Blackwell.

Singh, S.B. 1977. Some observations of diurnal vertical fluctuations in a pond having permanent bloom a of Microcyatin flos-squao. J. Inland Fish Soc. India 9 : 125–130.

Singh, H.n., K. Kumar, S.K. Sarkar and A.K. Ghosh. 1980. Observation on the diurnal fluctuation of oxygen and fish mortality during acute summer months in large weed infested pond of Kaushalyagang. Proc. Vth All India Congress of Zool. 120 p.

Van Duijn, C. Jr. 1973. Diseases of fishes. ILIFRR Books London : 372 pp.

Ward, H.B. and C.C. Whipple, 1918. Fresh water biology (ED) W.T. Edosnmon. Copyright (c), 1959). by John Wiley & sons Inc. New York London 1248 pp.

TABLE - 1

Certain physico-chemical and biological/microbiological properties at the time of fish kill incident

TABLE III

Stocking and fish kill records

TABLE IV

Results of bioassay experiment