SHORT COMMUNICATION

Bacterial flora of fish feeds and organic fertilizers

for fish culture ponds in Ghana

J A Ampofo1 & G C Clerk2

1Water Research Institute, CSIR, Box AH 38, Achimota, Ghana2Department of Botany, University of Ghana, Legon, Ghana

Correspondence: Dr Joseph AddoAmpofo,Water Research Institute, CSIR, Box AH 38, Achimota, Ghana. E-mail: jaampofo@yahoo.com

Use of animal manure to fertilize ¢shponds hasbeen reported in many parts of the world (Bardach,Ryther & McLarney 1972; Woynarovich 1979; Hop-kins, Cruz, Hopkins & Chong1980; Oladosu & Ayinla1992; Ayinla, Oladosu, Ajiboye & Ansa 1994; Njoku1997). In Ghana, poultry manure, cow manure,pig manure and cow blood from abattoirs aremostly used to fertilize ¢shponds. Some farmersmake periodic applications at 3- or 4-month inter-vals. Others depend on visual observation and addthe fertilizer according to the colour of the pondwater. Others do it once in the production cycle ofthe pond.The use of animal wastes to fertilize pond farms as

practised in manycountries is considered superior toinorganic fertilizers in producing and maintainingdesirable species of planktonic and benthic organ-isms (Pillay 1992) and to enhance ¢sh production(Edwards1980;Yadava & Garg1992; Garg1996; Garg& Bhatnagar 1996). As manuring causes organicenrichment, it may also hasten the deterioration ofthe water quality making the aquatic environmentfavourable for the growth and multiplication ofhuman pathogenic bacteria (Garg & Bhatnagar1996). Pathogenic bacteria such as Aeromonas, Citro-bacter, Edwardsiella, Enterobacter, Escherichia coli,Klebsiella and Serratia may be introduced into theaquatic environment (Cuelin 1962; Rao, Parhad, Rao& Rao 1968; Cohen & Shuval 1973; Evison & James1973; Allen, Austin & Colwell 1983; Austin & Austin1993; Ringo, Strom & Tabachak1995).Food is one of the chief vehicles of gastrointestinal

disease, and limits have therefore been establishedfor the numbers of pertinent categories of microor-

ganisms tolerable in various foods (Statutory Ordersand Regulations1955;Thatcher & Clark1968; Powers,Ay & Rowley1970).Fish farming in Ghana has been more on the sub-

sistence level and most farmers do not use commer-cial feeds. They mostly depend on household wasteand other agricultural byproducts of low price. Tothem, any item that sustains the ¢sh is food. Thiscommunication is intended to make workers of ¢sh-ponds using these feedstu¡s and fertilizers aware ofthe microbial burden of the inputs used in ¢sh farm-ing in Ghana.Knowledge of the resident micro£ora of ¢shpond

inputs will help to control and prevent diseases of mi-crobiological origin. The bacteriological quality of lo-cal agricultural byproducts and waste used as inputsfor aquaculture in Ghana has been assessed for theirpublic health risk. Materials assessed included 11diets and ¢ve organic fertilizers commonly used bythe farmers.Eleven feeds, banana (waste) collected from traders

from the market, biscuit (waste) from a local biscuitfactory, bread (waste) from sellers, brewery spentgrain from the brewery, cassava (waste) from foodproducers, corn bran from the corn mill, fufu (left-overs) from food vendors, groundnut bran from thegroundnut mill, rice bran from the rice mill, termites(dead) collected from termitarium and wheat branfrom the £our mill, and four organic fertilizers, dryblood (cow) from the abattoir, cow manure, pig man-ure and poultry manure were tested for bacteriologi-cal contamination.An amount of 10 g of each sample was transferred

to a sterile blender (Moulinex, EC) containing 90mL

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of 0.1% (wt/vol) peptone water and blended at highspeed for 2min. A duplicate sample was prepared foreach test. Heterotrophic bacterial populationwas as-sessed using the pour plate method and standardplate count agar. Colony-forming units (cfu) werecounted after incubation of the plates at 37 1Cfor 48 h. MacConkey broth was used for estimationof Enterobacteriaceae, and faecal coliforms werecon¢rmed by separate loop transfers from thepositive total coliform tubes to EC medium andincubated at 4470.5 1C. Sodium azide broth wasused for estimation of presumptive and con-¢rmation tests of faecal streptococci (StandardMethods1995).The total heterotrophic bacterial count of the 11

agricultural waste and byproducts o¡ered as feed to¢sh ranged from 0.7�103 to 1.9�104 per gram ofdiet.The count for the organic fertilizers ranged from1.4�106 to 7.3�106 per gram of fertilizer. The mostprobable number (MPN) per gram of coliforms of theorganic fertilizers was signi¢cantly greater thanthose of the diets, and ranged from 1.1�104 to9.3�104 per gram and o1^1.4�103 per gram fortotal and faecal coliforms respectively. Total coliformcounts for the11diets ranged from1.1to1.1�102 pergram. Faecal coliforms were detected in only three ofthe diets, namely biscuit waste, groundnut husk andtermites (Table1).

Enterobacteriaceae were detected in all 11 feedsand four organic fertilizers with the MPN beingfar superior for the organic fertilizers. The orderof magnitude did not, however, follow that of theheterotrophic bacterial count.Only three of the11feeds, biscuit waste, groundnut

husk and termite (dried), and three out of the four or-ganic fertilizers, cow manure, pig manure and poul-try manure, contained faecal coliforms. The countswere signi¢cantly higher for the organic manuresthan for the feeds. Again, only four out of the 11feeds, biscuit waste, cassava, groundnut husk andtermites, contained faecal streptococci, but the strep-tococci were present in all four organic fertilizers.Because most ¢sh ponds in Ghana are closed sys-

tems, feeds, fertilizers, their breakdown products andmetabolites will accumulate in the water column andpond sediment. These accumulated materials havebeen reported to have adverse e¡ects on ¢sh growth,survival and production (Garg & Bhatnagar1996).Although no species isolation was made in this

study, the detection of coliforms in the feeds indicatesthe presence of potential contaminationwith entericpathogens. These diets are often handled by childrenand could cause infection bydirect ingestionor by in-direct transfer of the pathogen to the mouth or re-spiratory passage via the hands. Consideration mustalso be given to the risk of skin andwound infections.

Table1 The bacterial load of feeds and organic fertilizers for ¢sh culture ponds

Most probable number (MPN) per 10 g

Material Heterotrophic bacterial count (�103 g^1) Total coliform Faecal coliform Faecal streptococci

Feed

Banana (waste) 0.7 93 ND ND

Biscuit (waste) 3.6 240 40 430

Bread (waste) 16 120 ND ND

Brewery spent grain 2.8 120 ND ND

Cassava (waste) 3 75 ND 40

Corn bran 1 43 ND ND

Fufu (left over) 19 1100 ND ND

Groundnut husk 7 75 10 200

Rice bran 1.4 11 ND ND

Termites (dead) 6 460 40 400

Wheat bran 0.9 40 ND ND

Fertilizer

Blood (cow) waste 5280 11� 104 ND 40

Cow manure 1490 39� 104 11� 103 23� 103

Pig manure 7300 93� 104 14� 103 43� 103

Poultry manure 2040 64� 104 9� 103 14� 103

Bacterial £ora in Ghanaian ¢sh culture ponds JA Ampofo & G C Clerk Aquaculture Research, 2003, 34, 677^680

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Farmers using these feedstu¡s must be aware of thepresence of the bacterial £ora as they will contributeto the ¢sh environment.The International Committee on Microbiological

Speci¢cations for Food of the International Associa-tion of Microbiological Societies has recommendedthat foods be examined for total viable mesophilicbacteria, staphylococci, salmonellas, clostridia, coli-forms and enterococci (Thatcher & Clark 1968). Thechoice of these organisms for the microbiologicalstandards was based on the participation of thesebacteria in the spoilage of foods as well as their invol-vement in food-borne epidemics and food poisoning.With ¢sh feeds, other considerations are important.Most ¢sh have been reported not to express food pre-ference (Klinger, Lawrence & Lawrence 1994) andwill pick anything introduced to them.Tropical waters have temperatures of around 30 1C

for most of the year and, as bacterial action andgrowth are nearly directly proportional to a tempera-ture rise from 21 1C to 30 1C (Axelrod & Schultz1969)and because the feed itself is a source of nutrients re-quired for bacterial growth, the pond water becomesan ideal culture medium for the pathogens present.Bacterial infections may be important causes offood-borne infection and other diseases in humans,particularly in Ghana where strict adherence to mi-crobiological speci¢cations for food are not respected.The results obtained could be used as the basis for

advice for the frequency of application of organic fer-tilizers, especially those that contain high loads ofthe bacteria. Furthermore, attempts should be madeto reduce asmuchas possible the bacterial load in thefeeds and fertilizers by appropriate treatments, suchas the use of solar energy to treat the feed andorganicfertilizers, and by storing the feeds under conditionsthat discourage rapid growth of bacteria.

Acknowledgments

This investigation received ¢nancial support from theGovernment of Ghana. The authors would like tothank the Director-general of the Council for Scienti-¢c and Industrial Research of Ghana, the Director oftheWater Research Institute, the Head of the Envir-onmental Biology and Health Division and the Headof the Department of Botany, University of Ghana forassistance. They are also grateful to the personnelof the Public Health and Reference Laboratory,Korle Bu Teaching Hospital. The co-operation ande¡orts of the sta¡ of theWater Research Institute areacknowledged.

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Keywords: ¢sh feed, organic fertilizers, ¢sh cultureponds, pathogenic bacteria, heterotrophic bacteria,coliforms

Bacterial £ora in Ghanaian ¢sh culture ponds JA Ampofo & G C Clerk Aquaculture Research, 2003, 34, 677^680

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