Chapter II Review of Literature 2.1 International status of intergrated farming 2.2 National status of integrated farming 2.3 Resident bacterial flora of fishes 2.4 Prevalence of fish diseases in aquaculture fish farms 2.5 Nutrient cycling by bacteria in aquatic systems 2.6 Degradation of organic materials by bacterial enzymes in aquatic system 2.7 NPK profile of aquaculture farms 2.8 Multiple drug resistance among bacteria of integrated farms 2.9 Serological characteristics bacteria from integrated farms 2.10 Influence of physico chemical parameters on aquatic ecosystem References
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Chapter II
Review of Literature
2.1 International status of intergrated farming
2.2 National status of integrated farming
2.3 Resident bacterial flora of fishes
2.4 Prevalence of fish diseases in aquaculture fish farms
2.5 Nutrient cycling by bacteria in aquatic systems
2.6 Degradation of organic materials by bacterial enzymes in
aquatic system
2.7 NPK profile of aquaculture farms
2.8 Multiple drug resistance among bacteria of integrated
farms
2.9 Serological characteristics bacteria from integrated farms
2.10 Influence of physico chemical parameters on aquatic
ecosystem
References
Chapter 2
Review of Literature
In recent years intensive fish culture is being practiced in the
brackish water, coastal water and fresh water impoundments of India and
aquaculture has been expanding rapidly, in an attempt to increase the
economy of our nation. This chapter aims to review the empirical and
theoretical information available from similar and related studies. A review
was conducted on the international and national status of integrated paddy
cum fish farming, diversity of bacteria from the different body parts of
cultured carps and wild fishes, bacterial load of water and sediment and its
diversity in aquatic system, prevalence of bacteria in nutrient enrichment in
integrated paddy cum fish farming, enzymatic activity of bacteria in
recycling of nutrients, characterization of the bacterial isolates from various
sources like fishes, water and sediment for their multiple drug resistance
and other serological properties and physico-chemical parameters of water
and soil in aquatic system.
2.1 International status of intergrated farming Integrated farming systems are new farming enterprises worldwide,
and the most efficient way of increasing self sufficiency of farm holdings
by increased resource utilization and thereby maximizing yields and
diversifying products. Stahl (1979) noted that decomposition of straw and
stubbles served as detrital supplements to prawns in aquatic ecosystems.
Khoo and Tan (1980) observed that introduction of herbivorous fish in rice
fields controlled weeds and reduced feeding cost. They also reported that
integration of fish farming with agriculture in Malaysia that the income
18 Chapter 2
from fish culture constituted 22 to 60 percent of farm income in single
cropped area of rice and 4 to 19 percent in double cropped area. They
concluded that fish formed a significant part of the total income of at least
60 percent of tenant farmers interviewed. According to them efficient
management was of utmost importance in increasing the profit margin. Nie
and Wang (1981) studied the relationship between rice and fish and found
that both benefit from each other. He called this mutualistic association and
this provided the theoretical basis for the expansion of rice-fish culture in
China. The Chinese were the pioneers of integrated farming and integration
of aquatic plant cultivation and fish farming has been in since the second
and first century B.C. (CFFCEB, 1982).
Guerrerro et al., (1982) reported the beneficial effects of fresh water
prawn as a stocking component in rice-fish integrated situation and noted
that when Macrobrachium rosenbergii was cultured along with rice, rice
plants provided feeding surfaces essential for the species. Miltner et al.,
(1983) found that rice straw detritus were good feed supplements for
prawns. Sevilleja and Lopez (1986) noted a significant saving in fertilizer
cost in rice production fields previously utilized for fish production.
Sevilleja (1986) demonstrated that rice fish integrated farming yielded
about 40% more income as compared to monoculture of rice. FAO (1988)
reported the observations of Chinese scientists on the apparent advantages
of rice-azolla-fish system and noted the increased grain yield, fish biomass,
and soil fertility, decreased incidence of pests, weeds and diseases.
Hu Bantong (1990) reported that 50kg of fish can produce enough
pond humus to fertilize six hectare of cropland. Light foot et al., (1990)
observed that integrated rice-fish system offered the possibilities of
Review of Literature 19
increasing rice yields by as much as 15% while continuous monocropping
of rice led to a decline in soil microbial biomass and fertility.
Identifying the importance of fish in Asian Rice Farming System, a
net work to popularize this practice had been mooted by IRRI and
ICLARM (Lightfoot et al., (1990). Costa Pierce (1992) reviewed the rice
fish farming practices of Indonesia and reported an annual yield of 63, 218
tones of fish from this system. Moody (1992) observed that under rice-fish
system, Cyprinus carpio not only eradicated weeds and algae in the rice
fields but also saved the cost on ploughing and harrowing. Nie et al.,
(1992) traced the mutualism of rice and fish farming and concluded that
grass carp controlled weeds thoroughly as compared to hand weeding and
herbicides. Wang (1992) suggested that, one of the most important farming
models suited for rice-fields is azolla-rice-fish integration.
The common carp Cyprinus carpio appeared to be better suited to
rice field environments of Philippines than Nile tilapia. Role of fish in pest
control in rice farming has been studied by Yuan (1992) in China and
reported that rice plant hoppers were reduced from a maximum of 104,000
to 70,776/hectare. Rice leaf rollers decreased from 210,000 to 120,000 per
hectare and grass carp (Ctenopharyngodon idella) were particularly
effective in controlling sheath blight. Experiments conducted with grass
carp (Ctenopharyngodon idella) in a rice-fish system in China showed that
they increased rice yields generally by 10% or more. C.idella controlled
weeds and harmful insects. By eating grass, they reduced the need for
farmers labour for weeding. C. idella faeces also helped to fertilize the rice
fields, Nie et al., (1992).
20 Chapter 2
Halwart (1994) reported that the rice crop benefits from the
presence of fish in terms of reduced pest incidence. Li and Paw (1994)
described that the rice fish culture in China is in the process of development
from extensive culture to semi intensive culture, from monoculture to
polyculture, and from self sufficient natural economy to commercial
economy.
Studies conducted by Halwart (1994) in Philippines on the potential
of biological control of common carp (Cyprinus carpio) and Nile tilapia
(Oreochromis niloticus) has reported that although fishes are not the single
solution to insect pest problems in rice fields, they do contribute to limiting
pest abundance and support the army of natural enemies of rice pests.
Common carps are found to be effective biocontrol agents against apple
snail pomacea (Pila globosa), the paddy pest in Philippines. Grass carps in
rice fields when polystocked with other species were found to manure and
fertilise pond water and generate natural food to filter feeders and
omnivores (Yang et al., 1994).
Fagi and Syamsiah, (1994) postulated that under optimum stocking
intensities in rice-fields, Cyprinus carpio enhanced availability of
phosphorus to rice. Fang et al., (1994) in the studies of pond water and
sediments of polyculture fish ponds observed the correlation between the
load of bacteria in fish pond and several environmental factors monitored.
Israel and Sevilleja (1995) reported that in Philippines rice fish culture
leads to higher rice production compared to rice monoculture. Shehadeh
and Feidi (1996) reported in Egypt, which is the second country in terms of
rice-fish area after China with 172. 800ha, almost 32% of the total
aquaculture production was contributed through rice-fish systems. The
Review of Literature 21
potentials of the integrated farming technology for transforming existing
traditional farming systems to become more sustainable in Ghana has been
reported by Lightfoot et al., (1996).
The integrated farming technology has became an appropriate
method for replenishment of decimated fish populations in the rice fields
with improvement of incomes, nutrition and environment for sustainable
operations and resource management to support healthy human life in
Bangladesh (Mazid and Hussain, 1996). Aldon (1997) reported the practice
of simultaneous rearing of crustaceans such as giant fresh water prawn M.
rosenbergii along with rice during the non saline phase in coastal fields of
Vietnam. He observed that approximately 80% of farm households in
Vietnam have their own small pond garden and canal for aquaculture.
Cagauan et al., (2000) reported from their case studies in Philippines that
fish and the nitrogen fixing aquatic fern Azolla and ducks integrated with
rice farming can result in nutrient enhancement, pest control, feed
supplementation and biological control.
2.2 National status of integrated farming Integrated farming system that depends on natural processes that
can convert organic wastes of one farming enterprise into useful byproducts
has been studied extensively by various authors, (Ardiwinata, 1957; Hora
and Pillay, 1962; Mears et al., 1974; Rabanal, 1974; Huat and Tan, 1980;
Chambers and Ghildyal, 1985; Richards, 1985; and Fresco and Poats,
1986). Country overviews on this system of farming have also been
provided for Bangladesh (Arce, 1985), China (Li, 1988) and India (Ghosh,
1992).
22 Chapter 2
Asia is considered to be the cradle of integrated crop-livestock -
fish farming and Sinha (1986) observed that the system helps to diversify
the income base of poor fisherman and small farmers. Reviews on
historical, socio-economic and ecological aspects of rice-fish farming by Li
(1988), Fernando (1993a), Halwart (1994), Mackay (1995), Choudhary
(1995) and Little et al., (1996) are available.
Ghosh (1980) while reviewing the prospects on integrated rice-fish
resource of 2.3 million hectare of deep water rice plots in the fresh water
sector, which would be used for rice-fish culture. According to his study
monocropped area under high monsoon precipitation is also potential areas
for utilization as fish/prawn culture systems during the summer fallow
period, particularly for raising prawns. Feasibility of monosex culture of
male tilapia (Oreochromis mossambicus) along with paddy in pokkali field
has been studied along the central coastal belt of Kerala and it was reported
that under the peculiar conditions of pokkali fields, Nile tilapia
(Oreochromis mossambicus) alone was found to be suitable for
simultaneous rice-cum-fish culture (Rajendran et al., 1981).
Muraleedharan (1981) in his article on “Resource use efficiency in
rice cultivation in low lying lands of Kerala” observed that inputs such as
human labour, bullock labour and fertilizers were not efficiently used in
cultivation of rice. Rajendran et al., (1981) conducted experiments in rice-
fish simultaneous culture in Pokkali fields of Kerala during 1977-78 and
observed that under ideal conditions production up to 183kg/hectare could
be achieved within 109 days period with Etroplus species. Since paddy
cultivation was not so economical, additional income gained through fish
culture was a great help to the farmers. There was also possibility of
Review of Literature 23
increasing production of paddy as Etroplus had helped in removing
Hydrilla.
Purushan (1986) in his study on recent advances in paddy cum fish
culture observed that the culture of fish and paddy together could
potentially increase and stabilize income on rice farms and also paddy post
fish culture increased the total annual yield. The fish could be beneficial in
eliminating weeds, molluscs and mosquitoes thus reducing labour cost. He
also studied the scope of paddy cum fish culture in Kerala and found that
the rate of fish production in paddy fields stood much better and suggested
the introduction of this practice in Kayal lands of Kuttanad and Kole, in
addition to 26,000 hectare of Pokkali Fields.
The apparent advantages of the Chinese practice of rice Azolla-fish
system in terms of increased grain yield, fish biomass, soil fertility and
decreased incidence of pest, weeds and disease have also been highlighted
by FAO and SIDA, (1988). Lightfoot et al., (1990) observed that integrated
rice-fish systems offer possibilities of increasing rice yields by as much as
15%. According to him, fish not only contribute to nitrogen accumulation
through their faecal excrements in the rice fields but also reduce nitrogen
loss. Fish can convert food into body tissues more efficiently than any other
farm animals. The food conversion rate is known to be 1-5 times more in
fish. The practice of utilization of rice fields for sequential farming of fish
and prawn is an age old practice in the pokkali rice fields of Kerala. These
are brackish water fields adjoining the Vembanad Lake. The practice is
popularly known as Chemmeenkettu or prawn filtration.
Studies conducted by the Kerala Agricultural University at the
Regional Agricultural Research Station, Kumarakom indicated that in
24 Chapter 2
addition to rice production averaging three tons per hectare, fish yield
ranging from 600 to 1000 kg/hectare could be obtained by simultaneous
farming of rice and fish.
As compared to the practice of simultaneous farming which requires
several modifications to the rice fields to protect the fish from the inherent
risk of pesticide applications, rotational farming of rice and fish was shown
to be more advantageous as it permitted better management practices for
both rice and fish (Padmakumar et al., 1990). In their investigations, where
in Indian major carps, common carps and Etroplus and the giant fresh water
prawn Macrobrachium rosenbergii were polycultured, yield touched
1005kg per hectare without any additional expenditure on feeding or
manuring. The integrated rice-fish rotational farming system for low lying
rice fields tested and developed by the Kerala Agricultural University at its
Regional Research Station, Kumarakom and introduced in Kuttanad a few
years ago as demonstration trial in farmer’s fields has become an instant
success. As a result there has been even an increase, though marginal, in
the area under rice in the low lying fields of Kottayam between 1997-98
and 1998-99 from 13754 hectare to 14393 hectare.
The study conducted by Padmakumar et al., (1990) indicated that
integrated farming of giant prawns (Macrobrachium rosenbergii) in
channels of coconut garden in the wetland area, adjoining southern portion
of Vembanad Lake is economically viable.
Identifying the importance of fish in Asian rice farming system, a
network to popularise rice-fish farming has been mooted by IRRI and
ICLARM (Lightfoot et al., 1990). Ghosh and Chakrabarti (1990) reviewed
the different works on farming of fish in rice fields in India and observed
Review of Literature 25
that monocrop rice fields under high monsoon precipitation and deep water
rice fields are ideal zones for integrated farming.
Kerala has extensive weed-checked water areas with low dissolved
oxygen suitable for the cultivation of air breathing fishes like Clarias
batrachus, Heteropneustes fossils, Channa striatus and Channa punctatus,
which have many cultural traits. Several culture fishes like Catla, Mrigal,
Rohu, Cyprinus has been widely cultured in fresh water bodies including the
paddy fields with supplementary organic feed (Sinha and Srivastava, 1991).
Growing the Chinese grass carp C. idella in integrated rice cum fish
farming system in eastern India increased the yield of rice by about 20%
and 35% and is attributed to the direct and indirect benefits of the control of
aquatic weeds and also to the additional manuring of the plots by grass carp
faeces. In the studies on the economic viability of poultry-rice and fish in
the lowland rice fields in Tamil Nadu, Rangaswamy et al., (1992) reported
an increase in profit margin by 60 per cent as compared to the conventional
farming practice.
Mukhopadhyaya et al., (1992) studied the relative advantages of
rice-fish integration in the deep water rice fields of West Bengal and
reported fish yields ranging from 263-1215kg/hectare. Tiwari (1993)
observed that a farming system involving flooded rice, poultry and fish had
a high degree of complementarity. The integration of fish and the nitrogen
fixing aquatic fern Azolla show promise for increasing the production
potential of the system.
Dube (1995) studied integrated aquaculture and found that, through
fish-paddy crop integration the production cost can be reduced to one third.
26 Chapter 2
It also reduced land erosion by 57 per cent. Weeds and insects were
controlled by fish as they feed on it. Fish cum crop integration led to
increased efficiency of resource utilization, reduced investment risk
through crop diversification and served as additional resource of food and
income. Influence of organic and inorganic fertilization on the growth and
nutrients of rice and fish in a dual culture system in Kharagpur, West
Bengal, India has been studied by Ghosh et al., (1995) and reported that the
total number of phytoplankton species as food for the fish under organic
manuring was more than under inorganic fertilization.
The integrated farming technology has become an appropriate
method for replenishment of nutrition and environment for sustainable
operations and resource management to support healthy human life in
Bangladesh (Mazid and Hussain, 1996). The potentials of the integrated
farming technology for transforming existing traditional farming system
into more sustainable system has been highlighted by Lightfoot et al.,
(1996). Singh and Swami (1998) in their studies in Punjab revealed that by
the integration of aquaculture with agriculture and use of supplementary
feed, a sustainable fish production of over 10 tones per hectare can be
easily obtained.
2.3. Resident bacterial flora of fishes The bacterial flora of living fish generally reflects the microbial
content of water, environmental factors, feeding habits and seasonal
changes. Colwell (1962) suggested that the methods of handling fish and
their pre capture environment influence the composition of the skin flora.
Lindsay (1986), Peleteiro and Richards, (1985) and Shewan (1961)
recorded Pseudomonas, Achromobacter, Flavobacter and Vibrio species in
Review of Literature 27
descending order of frequency on gills of marine fish from the north sea
and Norwegian water, whereas only Bacillus and Micrococus were isolated
from gills of fish from warmer waters of India. These differences probably
reflect differences in environmental temperatures, with more psychrophiles
and fewer mesophiles in the cold north sea water.
The intestinal microflora of fish reflects the bacterial content of
ingested food and water, Seki (1969), Horsley (1977) and Tanasomwang
and Muroga (1988). Horsley (1973) examined bacteria from the skin of
Atlantic salmon in marine, estuarine and fresh waters. The frequency of
genera isolated varied at different sampling sites, and the major
components of the skin flora were similar to those present in the water,
again indicating that the external flora of fish are a reflection of their
environment. Sera and Ishida, (1972) studied that the stomach and
intestinal content of fish closely reflects the bacterial flora of their diet.
An investigation of the aerobic and anaerobic heterotrophic intestinal
flora of gold fish Carassius aurates demonstrated that the intestinal microflora
became relatively stable at about 67 days after hatching and consisted of
Aeromonas hydrophila, Pseudomonas, Clostridium, Bacteroides type A,
Enterobacteriaceae, Plesiomonas, Shigelloides and Moraxella. These
transients were also detected in fish diets and fish eggs, and in water or
sediment, but did not become established in the intestines.
Horsley (1973) studied the bacterial genera on the gills of Atlantic
salmon migrating up the Dec River in Aberdeenshire, Scotland showed that
the relative numbers of the different genera changes with changes in the
environment of the fish from the marine to fresh water. Trust and Sparrow
(1974) found that numbers of bacteria in fresh water Salmonoids increased
28 Chapter 2
between the stomach and the posterior portion of the intestine. They
suggested that these numbers must represent active multiplication in the
tract as they could not be accounted for by ingestion.
Trust and Sparrow (1975) calculated that the area of gills covered
by bacteria would be only 0.02%. Yoshimizu et al., (1976) determined that
the intestinal microflora was simpler than those of the surrounding waters,
consisting of Aeromonas and Enterobacteriaceae in fresh water reared fish
and Vibrio in fish from sea water. A study in Finland by Niemi and
Thaipalinen, (1982) showed that effluents from two fish farms had elevated
numbers of total coliforms and fecal coliforms and on one farm effluent
had more fecal Streptococci than the influent. The majority of coliforms
identified were Enterobacter and Citrobacter and Aeromonas hydrophila
were quite common. The percentages of Gram-positive bacteria including
Bacilli, Cocci and Coryneform bacteria were markedly higher in natural
fish than in cultured ones, Clostridium and sulphate reducing bacteria were
commonly isolated from natural fishes (Sakata et al., 1984).
Quantitative and qualitative studies on the bacterial flora of freshly
caught pearl spot Etroplus suratensis from Cochin backwaters revealed that
the microflora of skin, gills and intestine consisted mainly of asporogenous
rods (Surendran and Iyer, 1985). Sugita et al., (1988) reported that the
permanent intestinal microflora consisted of bacteria which were also
present in the surroundings but which were able to persist and grow in the
environment provided by the intestinal tract.
Austin (1988) isolated the surface micro flora from the skin of
healthy turbot was Photobacterium angustum, Photobacterium loga,
Alcaligens feacalis, Pseudomonas fluorescens and Bacillus firmus. These
Review of Literature 29
bacteria may also have been present in the water as a result of being shed
from fish, but in numbers too low. The mucus of the gills, gut and skin of
fish contains lysozyme and immunoglobulins which presumably act as
defense mechanisms against bacteria.
Various aspects of the normal microbial flora associated with fish
have been studied by Cahill (1990). Generally the range of bacterial genera
isolated is related to the aquatic habitat of the fish and varies with factors
such as the salinity of the habitat and the bacterial load in the water.
In integrated farming system, the contribution of bacteria as major
feed source for fish filter feeding and omnivorous species has been
illustrated by Guo et al., (1994). Importance of biofilms in fish processing
and aquaculture industry is being increasingly recognized and the role of
bacterial biofilms as a source of pathogens has been reported by
Karunasagar et al., (1994) and Tonguthai (1995). Geldreich and Clarke
(1996) reported that bacterial flora of aquatic animals especially that of fish
and shell fish is a reflection of their environmental flora. Aquatic animals
take up various kinds of bacteria from food, water and sediments which
may become constituent of bacterial flora of the digestive tract (Yoshisuke
et al., 2000). The aquaculture products can also be a source of various
bacterial, viral and protozoan pathogens. The contamination can occur
from various sources such as water, feed, pond, soil, bird droppings and
other live forms of surrounding ecosystems (Hus et al., 2000).
The composition of the bacterial flora of Black clam Villorita
cyprinoids from Vembanadu Lake in Kerala reveals a total of 55 bacterial
strains. The mesophilic flora was dominated by genera Vibrio, Aeromonas
and Pseudomonas. The total bacterial flora of clam consisted of about 72%
30 Chapter 2
gram-negative and 28% gram-positive genera (Lalitha and Surendran,
2005). The percentage contribution of different bacterial groups in the
biofilms of water seemed to be fluctuating, but Vibrio, Aeromonas,
Pseudomonas and Bacillus were isolated on most of the occasions (Das et
al., 2007).
2.4 Prevalence of fish diseases in aquaculture fish farms Fish disease is one of the most important problems that severely
affect the economic balance of aquaculture farmers. Innumerable diseases
were caused in fishes due to bacterial pathogens and several of them were
reported from India. Gopalkrishnan (1961) and Kumaraiah (1977) studied
an endemic bacterial disease caused by A. liquifaciens infecting the eyes of
Catla leading complete necrosis and death of the fish. Corneal opacity in
silver carp, (Hypophthalmichthys molitrix Val.) due to Gram-positive
bacterium, Staphylococcus aureus was reported by Shah and Tyagi (1986).
Mycobacterial organisms have been attributed to a condition known as gill
hyperplasia syndrome in common carp (Cyprinus carpio) as reported by
Kumar et al., (1986d). Ulcerative diseases in Calta have been reported to
penetrate the opercular bones and cranium. Gopalkrishnan (1963) and
Karunasagar et al., (1986) have investigated several such outbreaks.
Several workers have reported the occurrence of the diseases in
composite fish culture ponds (Pal and Tripathi, 1978). Recovery of human
enteric pathogenic bacteria indicates the extent of pollution by domestic
sewage (Prabhakar et al., 1985). The presence of virulent strains of
Aeromonas in healthy fish suggests their role as an opportunistic pathogen.
Dropsy is another important fish disease in India were Rohu (Labeo
rohita), Catla (Catla catla) and Mrigal were affected mostly in the late
Review of Literature 31
winter. Kumar et al., (1986a) revealed a mixed infection of A. hydrophila
and myxosporidian parasite in the case of infectious dropsy in Catla catla.
Vibrio species were found to be frequent and apparently
opportunistic pathogens of Pennaeid shrimp (Lightner, 1988). Vibrio
appears to be influenced by the physico chemical features of the
environment (Cheng and Cheng, 1988). It is very important to assess the
presence of pathogens and environmental quality of the medium where
aquaculture is practised. Jhingran (1991) also observed eye diseases in
endemic forms of Channa mauritius and attributed it to the same type of
organisms. Mukherjee et al., (1992) have recorded a mass mortality in
farm reared silver carps and isolated Staphylococcus aureus from the
affected eyes of diseased fish.
Salmonella is an important bacterial pathogen associated with food
borne illness in most of the countries of the world. Nambiar and Iyer (1991)
have reported prevalence of 16 different serotypes of Salmonella in frozen
shrimp and frozen fish samples from Kochi. Nitrogen fixing bacteria
Azotobacter and the obligate anaerobe Clostridium were found abundant in
sediments and in the overlying water. Mukherjee et al., (1991) have
reported the role of A. hydrophila in ulcerative disease of fish and identified
the biochemical differences among the various strains of these organisms.
Nayak and Mukherjee (1994) made a detailed study of the
biochemical properties of A. hydrophila and drawn antibiograms on the
basis of antibiotic sensitivity tests. In a recent study these workers were
elucidated the role of A. hydrophila in dropsy, fin and tail rot and more
elaborately in epizootic ulcerative syndrome. It was also reported the role
32 Chapter 2
of ulcerative disease in necrotizing the muscle tissue and internal organs
like kidney, liver and spleen.
The presence of faecal coliforms and Streptococci in the intestinal
tract and water is an indication of water pollution with faecal material of
man and animals. The agro ecosystems and backwaters of central Kerala
were found to provide habitats for avian fauna in high population density
and they act as the main source of faecal contamination of fresh water
sources (Panicker and Ravindran 1997). Innumerable diseases were caused
in fishes due to bacterial pathogens and several of them were reported from
India. Some of the important bacterial pathogens like Aeromonas
hydrophila, A. salmonicida, Pseudomonas fluorescens, P. putrefaciens,
Vibrio parahaemolotyticus, V. alginolyticus etc. had been identified as most
commonly encountered agents in fish diseases (Mukherjee, 2002).
Coliform bacteria occur in large numbers in faeces and sewage but
are also found in the environment in the absence of human faecal
contamination. Faecal Streptococci were also found occasionally in small
numbers in food and environmental samples. The spores of sulphite
reducing Clostridium perfringens also can survive in the environment.
Pseudomonas aeruginosa also rapidly occur in a wide variety of aquatic
habitat yet it is not always found in human faeces. But it is an important
opportunistic pathogen and a cause of food spoilage as reported by Mackie
and Mc Cartney (2006).
2.5 Nutrient cycling by bacteria in aquatic systems Biochemical transformations of particulate and dissolved detrital
organic matter by bacteria and fungi are fundamental to the structure and
dynamics of nutrient cycling and energy fluxes within aquatic ecosystems.
Review of Literature 33
The decomposition of organic matter by bacteria is governed by many
factors, particularly chemical, biological and physical parameters of the
ecosystem. The regeneration of organic nitrogen by bacteria is carried out
by decomposition and utilization of nitrogenous organic matter in the
aquatic systems (Botan et al., 1960).
Bacteria and fungi assimilate dissolved organic compounds. Some
of which are those they obtained through enzymatic degradation of
particulate organic matter. The decomposition rate of organic substances is
greatly dependent on solubility as reported by Vallentyne (1962). The rate
of decomposition of detrital substrates is a function of their concentration
and of the enzymatic activity of the surfaces of detrital particles (Saunders,
1972b).
Radheshyam (1986) studied the role of microorganisms playing
with organic nutrient cycling in fish ponds and improving the pond
heterotrophic production for maximum yield of fish in integrated farming
systems. Nitrogen transformations include assimilation, mineralization,
nitrification and denitrification in sediments (Rysgaard et al., 1993). Fang
et al., (1994) in the studies of pond water and sediments of polyculture fish
ponds observed the correlation between the load bacteria in fish pond and
the seasonal environmental factors monitored. Bacteria of the genus
Pseudomonas were found commonly occurring in both pond water and
sediment, there were changes or replacement of dominating bacteria along
with the seasons.
Microorganisms occupy the same environment without affecting
each other. Soil microorganisms serve as biogeochemical agents for the
conversion of complex organic compounds into simple inorganic
34 Chapter 2
compound or into their constituent elements (Pelczar, 2001). The metabolic
activity of microorganisms solubilizes phosphate from insoluble calcium,
iron and aluminium phosphates. Phosphates are released from organic
compounds such as nucleic acids by microbial degradation (Pelczar, 2001).
Biofilms of water are important biological structures formed on most
submerged aquatic surfaces. They comprise a unique niche wherein
communities of microorganisms co-exist. The common bacterial genera
comprised Pseudomonas, Vibrio, Aeromonas and Bacillus as reported by
Das et al., (2007). The load of bacteria in the biofilm was similar to that
found in the corresponding water.
2.6 Degradation of organic materials by bacterial enzymes in aquatic system Cellulolytic micro organisms play an important role in the biosphere
by recycling cellulose, the most abundant carbohydrate produced by the
plants. All organisms are known to degrade cellulose efficiently by
producing a number of enzymes with different specificities which may act
together in synergism. Minami et al., (1972) identified chitin decomposers
from the digestive tracts of ayu (Plecoglossus altivelis), carp (Cyprinus
carpio) and rainbow trout (Salmo gairdneri) and found that Aeromonas
species from freshwater fish and mainly Vibrio from marine fish are mainly
chitin decomposers. Microbial breakdown of substances such as cellulose
and chitin, in the gut could make nutrients available for absorption.
Cellulose activity was found to occur in the stomachs of 17 of 62 fish
species examined and was apparently due to the production of this enzyme
by gut microflora (Stickney and Shumway, 1974).
Review of Literature 35
Trust et al., (1979) tested the ability of bacteria from the intestine of
grass carp to break down cellulose and found that Aeromonas hydrophila
was capable of breaking down cellulobiose but not cellulose or carboxy
methyl cellulose. The cellulase activity was derived from gastrointestinal
microorganisms rather than the presence of cellulase in the food
consumed. Cellulose activity in fish is correlated with the ingestion of
invertebrate cellulase or cellulolytic bacteria associated with the food
(Prejs and Blaszcyk, 1977; Lindsay and Harris, 1980), and that
populations of gastro intestinal micro organisms from fish exhibit little
cellulase activity (Trust et al., 1979; Lesel et al., 1986; Anderson 1991).
Cellulolytic bacteria have been known and investigated for many
years (Bisaria and Ghose, 1981). Madden (1983) reported many cellulolytic
bacteria from soil, compost, manure, muncipal soild waste etc. Lesel et al.,
(1986) detected both amylolytic and proteolytic bacteria in the gut of
phytophagous gold fish, C. auratus. Stevens (1988) reported that microbial
fermentation and nutrient synthesis are typically important in organisms
with a diet high in fibre. As vertebrates are incapable of producing cellulase
endogenously, exogenous cellulases play a critical role in the nutrition of
vertebrate herbivores.
Cellulose is an unbranched glucose polymer, composed of anhydro-
D-glucose units linked by 1,4βD glucoside bonds, which can be hydrolysed
by cellulolytic enzymes produced by both bacteria and fungi (Robson and
Chamblis, 1989). Cellulolytic bacteria include aerobic species such as
Pseudomonas and Actinomyces, facultative anaerobes such as Bacillus and
Cellulomonas and strict anaerobes such as Clostridium. Most of the
mesophilic isolates produced amylases and proteases, and 38% of isolates
36 Chapter 2
produced extra cellular enzymes; amylases, proteases, cellulases and
chitinases.
Cellulose fermenting bacteria that fix nitrogen may be widespread
and may play a role in nitrogen cycling as well as in carbon cycling on a
global scale (Leschine and Parola; 1989). Cellulose, the largest renewable
carbon source available, (approximately 150 billion tons of organic
material is photosynthesized annually) is frequently found in close
association with other compounds such as hemi cellulose, lignin and other
polysaccharides which makes its bioconversion more difficult (Person et
al., 1990). Das and Tripathi (1991) reported cellulase producing bacteria as
a part of intestinal flora and were not introduced with food. Gilkes et al.,
(1991) reported that the species of Pseudomonas, Cellulomonas,
Clostridium, Bacteriodes and Streptomyces can produce glycosylated
cellulases. As the diet was mainly composed of carbohydrates resistant to