Assessment of post-harvest losses in the Nigeria fishery: the Kainji lake model

A.A. Eyo
National Institute for Freshwater Fisheries
New Bussa, Niger State, Nigeria

and

M. Mdaihli
Nigerian/German (GTZ) Kainji lake Fisheries
Promotion Project
New Bussa, Niger State, Nigeria

1. INTRODUCTION

Fish is a highly perishable commodity. The rate of spoilage is influenced to a large extent by the high ambient temperature. Consumers generally demand and pay more for good quality fish. Poor quality fish constitute an economic loss to fishermen and fish traders. If losses are quantified it would be possible to verify at what stages of the distribution chain serious losses occur and so pay more attention to reducing losses at these stages. This will have a direct impact on the fishery. This paper has been prepared with the objective of describing a methodology for quantitative assessment of post-harvest losses. This method has been developed and used in Kainji Lake area with success, and is recommended for application by scientists involved in data collection on post-harvest losses.

2. METHODOLOGY

In a total of 45 villages (out of approximately 250) 314 fisher folk, 115 fish processors, 125 fish buyers and 111 fish sellers were interviewed using standardised questionnaires. Since the total population for each group of respondents was not known, random sampling was not possible. Instead, respondents available at point of the visit were interviewed. The field survey lasted 24 days between April 1996 and June 1996. The interviews were carried out by two male and two female Hausa/English speaking data collectors under supervision of a fish processing expert. Before the start of the fieldwork, the data collectors were trained in questionnaire administration, fish identification and organoleptic assessment of the quality of fresh and processed fish. The questionnaires were tested at Anfani - a fishing village close to Kainji Dam. The questionnaires were administered to fisher folk, fish processors and fish traders at various periods during the day. Samples of the questionnaires are shown in annex 1, 2, 3 and 4. On-the-spot assessment of the fish quality was carried out systematically in each boat, at the processing site, and in the market as required during the interview.

3. RESULTS AND DISCUSSION

The model that is used to assess the post-harvest losses in Kainji Lake fishery implies the following channel that is employed to bring fish from the producer to the consumer: Fisherman to Fish processor? to Fish seller? to Fish buyer? to Consumer. At each stage in the distribution chain, there are post-harvest losses that can be divided into losses during handling by fishermen, losses during processing by the fish processors and marketing losses that occur after the fish is processed until it reaches the consumers.

3.1 Handling losses

Fish catches

During sampling, the total number of fish caught was 24 839 (2389.3 kg) consisting of 43 fish species. Tilapia (Oreochromis niloticus) was the dominant species by weight (357.27 kg), followed by Nile perch (Lates niloticus) (210.31 kg), Citharinus cithanus (193.7 kg), Synodontis membranaceous (164.12 kg) and Labeo senegalensis (159.63 kg).

Fish spoilage at checking and landing

At checking, Clarias anguillaris had the highest spoilage rate with 23% by weight closely followed by Alestes macrolepidotus (22%), Distichodus brevipinnus (22%) and Hydrocynus forskalii (18%). The least percentage loss at checking was 0.33% from Auchonoglanis biscullatus. Fish being removed from fishing gears are sometimes roughly handled and most of the time dropped in the open at the canoe bottoms under the prevailing high temperatures. Rapid deterioration particularly through bacterial decomposition under the warm conditions sets in.

At landing, Labeo senegalensis recorded the highest level of spoilage by wt (17.36%) followed by Chrysichthys auratus (8.49%), Labeo coubie (5.67%) and Hydrocynus forskalii (5%). The least spoilage was observed in Chrysichthys nigrodigitatus with less than 1%. Oreochromis niloticus that was highest in catch had 10% spoilage at checking and 4% at landing.

Some species did not record any spoilage at checking and landing for the following reasons:

- they were either caught with active gears and therefore did not spend long time in the water before checking and landing (Sierrathrissa leonensis and seine net by-catches),

- they were too few in the catch samples measured to make any meaningful impact.

- they have ancillary breathing organs which enable them to stay alive for many hours in the net until the fish is landed (for example, Synodontis species).

Table 1: Fish spoilage (sample) by fishing gear

GN = Gillnet, LL = Longline, TR = Fishing Trap, CN = Castnet

Table 2: Fish spoilage (total) by fishing gear

GN = Gillnet, LL = Longline, TR = Fishing Trap, CN = Castnet

Fish spoilage according to gear.

Passive gears such as gillnets were mainly set in the evening and checked before noon. Active gears for example, cast nets and beach seine were operated respectively at any time of the day. In addition, beach seines for Clupeids were operated almost hourly throughout the day/night.

In the sample gillnets accounted for 79% of the fishing gears used by the artisanal fishermen followed by cast nets (9%), hooks (7%), traps (4%) and beach seines (1.4%). Of the total sample catch assessed 10.5% was spoiled at checking and additional 3.4% got spoilt when the catch was finally landed (Table 1). From extrapolations made using the 1995 catch estimates for Kainji Lake (Catch Assessment Survey of KLFPP), out of the total gillnet landings of 5 778 tonnes about 800 tonnes got spoilt. For long lines, the spoilage rate at checking and landing is very low, about 28.5 tonnes of the estimated 2 383 t fish landings in 1995 (Table 2).

Considering the total catch from gillnets, long lines, traps and cast nets estimated at about 14 000 t in 1995, about 1 000 t of fish lost their value or had to be discarded due to spoilage. Assuming an average price of 80 Naira per kg of fish, the loss to the economy amounts to 80 million Naira per year (on the basis of 1995 figures).

3.2 Processing losses

Fish smoking

In the survey the major fish processing method was fish smoking (and roasting) accounting for 89% of the sample. Smoking was carried out in traditional fish smoking kilns "Banda" using wood; sometimes cow dung is added to impart the golden colour. Smoking was mainly done by female fish processors (57%), who are mostly fishermen's wives or by migrant fish traders. During smoking in "banda" ovens the fish loses over 50% of its weight. In the sample a total of 9 495 fishes weighing 987.18 kg was purchased by fish processors out of which 22% by number and 16% by weight was spoilt before smoking. This suggests that fish processors purchased spoiling fish from fishermen or left some of the good quality fish to deteriorate believing that smoking would mask the spoilage. But since smoking does not improve the quality of spoilt fish such smoked product have off-odour and break easily. Only 15 of fish by number and less than 1% by weight deteriorated after smoking which shows that the fish processors were in full control of the smoking process. Fish were seldom gutted before smoking resulting in enhanced bacterial spoilage and bitter taste due to bile. Fish that are insufficiently dried-smoked having moisture content of 40% or more are prone to attack by Rhizoctonia sp., Penicillin sp. and Aspergillus sp. To check these types of infestation re-drying or re-smoking before sale is often necessary, resulting in an increase of processing costs. These costs are passed on to the consumers. Data on the actual losses of dried/smoked fish due to fungal infestation are rare in the literature. However, personal observation at the major fishing villages and markets in the Kainji lake basin revealed that substantial quantities of fish are usually infested by fungal growth.

Sun drying

Sun drying accounted for 10% of the sample during the field survey. Clupeid was the only fish sun dried on the lake basin. In the drying process Clupeids may lose half of its fresh weight due to moisture loss and/or attack by vermin. When caught in the day, Clupeids were immediately spread out either on cemented floor or polythene sheets with little or no spoilage since they dry within twelve hours. One of the major causes of spoilage during or after drying is the rush to get the fish to the market. Improperly dried fish is more susceptible to blowfly/beetle infestation in storage. The indiscriminate method of mixing wet fish with properly dried ones encourages cross infestation of fish being packaged for distant consumer markets. Spoilage of Clupeids can also occur when the night catch are stored in a pouch net inside the canoe or left exposed for drying the following morning. Spoilt dried Clupeids can be distinguished from the good quality ones by the colour. Clupeids that are immediately dried after landing are light brown with some sheen. Dried clupeids that were spoilt before processing are greyish and dull. Clupeids with signs of spoilage lose market value by 30%.

Frying

Fish frying accounted for less than 15 of the sample. Fish fried in groundnut oil is prepared in the markets for immediate sale to consumers. The fish are washed but not gutted. They are fried until dry and brittle. The commonest fried fish during the survey were tilapia and moonfish.

Table 3. Duration of storage of fish by fish sellers before marketing.

3.3 Marketing losses

Intensive fish marketing is carried out on market days (either Fridays or every four days). Before marketing fish is often stored in fishing villages to enable the fish sellers stockpile their fish before disposal (Table 3).

During the period of storage some fish may undergo spoilage due to bacterial action on insufficiently smoked fish and insect infestation of dried fish. Out of the total fish sold by fish sellers 16% were spoilt. Fresh fish for sale are not gutted. To improve the shelf life of captured fish in the absence of ice and freezing facilities live table-size fish are also available for sale in the markets. These live fish are kept in bowls of water. To avoid spoilage during long distant transport the fish is packed in cartons. The carton bottom is covered with thick brown paper or dry grasses to seal all crevices and provide a cushion for the fish to avoid breakage. When the carton is packed with fish, a mixture of groundnut oil and water is sprinkled (or blown with the mouth) over the top layer, to give the fish a shiny appearance. An unspecified insecticide, "Otapiapia" is sprinkled all over the fish and the inside of the carton to prevent insect infestation. The fish is then covered with thick brown paper. Table 4 shows the quantity of fish purchased and the level of losses from spoilage in each container.

Table 4. Quantity of spoilt fish purchased by fish buyers

The total spoilage was 6.38% of the weight of fish bought. The spoilt fish were downgraded and sold at a much lower price to be used essentially as fish meal in livestock feeds. The unhygienic conditions in mud walled store houses around Lake Kainji also contribute to fish losses. Packaged fish are often left on the floor of the stores where they can get humid resulting in rapid insect and fungal infection that makes the fish unsightly for marketing. Temperature changes between the fish directly resting on the bare floor and those in the upper units of cardboard, jute or basket packages have been observed to vary by as much as 15ºC by Osuji (1974). These temperature variations encourage infestation by beetle pests and often lead to serious loss of fish quality in storage.

4. CONCLUSION

The high post harvest losses recorded in gill net, long lines, traps and cast net catches valued at 80 million Naira indicate the level of economic loss caused by the prevailing traditional fish handling methods. When the losses at processing, storage and marketing are included, the level of post harvest losses in the lake fishery would be much higher. Based on this, any management strategy for Kainji lake fishery must also take cognisance of the high post harvest losses in the lake basin if it is to create the much-desired impact in the nation's economy and protein availability.

5. REFERENCES

Amos, T.G. (1968). Some laboratory observations on the rates of development, mortality and oviposition of Dermestes frischni J.Stored Prod. Res. 4: 108-117

Awoyemi, M.D. (1988). Insect infestation of dried fish in the Kainji Lake area. NIFFR Annual Report 1988. 183-190

Anthonio, Q.B.O. (1995). Fish marketing Survey in the Kainji Lake Basin Report prepared for the Nigerian-German (GTZ) Kainji Lake Fisheries Promotion Project

Dada, B.F. & Gnanados, D.A.S. (1983). Nigerian Fisheries Development: Challenges and opportunities of the 1980's. In the proceedings of the 3rd Annual Conference of the Fisheries Society of Nigeria (FISON) Maiduguri 22-25 February, 1983

Eyo, A.A. (1977). An appraisal of the traditional fish handling and processing in Kainji Lake area. KLRI. Newsletter 3 (2) 1977.

Eyo, A.A. (1993). Shelf-life of Moonfish (Citharinus citharius) and Trunk fish (Mormyrus rume) during storage at ambient temperature and on ice. Proceedings of the 6th FAO Export Consultation on Fish Technology in Africa, Kusumu, Kenya.

FAO. (1981). The prevention of losses in cured fish. FAO Fish Tech. Papers. No. 219. FAO. Rome.

Meyboom, B. (1975). Fish handling and processing in the Kainji Lake Basin and suggestion for improvements and future research in FAO Rome FIDP/NIR/66/524/12.

Osuji, F.N.C. (1974). Recent Studies on the infestation of dried fish in Nigeria by Dermestes maculatus and Necrobia rufipes with special reference to the Lake Chad district. Trop. Stored Prod. Inf. 29: 21-32.

Tobor, T.G. (1984). The fisheries industry in Nigeria: Status of fish preservation methods and future growth pre-requisites to cope with anticipated production. In: Proceedings of the symposium on fisheries development. Sponsored by Almarine, 31 August 1984

Tobor, J.G. (1993). Finfish and shellfish of conservation interest in Nigera. Proceedings of the National Conference on Conservation of Aquatic resources edited by Eborge et al National Resources Conservation Council (NARESCON) 1993. pp. 104-129

The effect of clove and ginger dip on quality of solar-tent dried (Clarias anguillaris)

by

C.A.Negbenebor and I.S. Adetunji
Department of Food Science and Technology
University of Maiduguri
PMB 1069, Maiduguri, Borno State, Nigeria

J.O. Igene
Department of Animal Science
University of Benin,
PMB 1154, Benin City, Nigeria

1. INTRODUCTION

Drying is a traditional and widely used method of preserving fish in tropical countries (Waterman, 1976) especially in the absence of refrigerated storage facilities. Nutritionally, fish proteins are noted for a high degree of digestibility and as a rich source of lysine and sulfur containing amino acids. Therefore it is suitable for complementing high carbohydrate diets especially in developing countries (Kent, 1984). Much attention is being directed at fresh water fish because of its health benefits, as a result of the presence of omega-3-fatty acids in the fish oil (Vileg and Body, 1988; Negbenebor, 1990). The reduction of these losses can only be achieved by systematic improvements in handling, processing, storage and distribution (FAO, 1990).

Clarias anguillaris is one of the most common fish marketed in Borno state and the lake Chad district. They are processed either by sun drying or smoking. This serves as a source of income for the fisher folks as sun dried fish is a highly relished item by all strata of the society especially in the north eastern state.

Spices such as clove and ginger are grown locally and have been known to enhance aroma and flavor of foods (Purseglove et al.,1981). Such spices could also have anti-microbial properties. The use of such spices either singly or in combination may actually enhance the quality of such processed fish products.

The objective of this study is therefore to investigate the effect of clove and ginger on microbiological and sensory qualities of solar-tent dried Clarias anguillaris.

2. MATERIALS AND METHODS

Collection of sample

Fresh live fish samples (Clarias anguillaries) were obtained from Gamboru fresh fish market Maiduguri, while the clove and ginger were obtained from Monday market Ltd, Maiduguri.

Preparation of the samples

The clove and ginger samples were ground using a hammer mill, wrapped in aluminum foil and autoclaved at a pressure of 15 PSI for 15 min and plated out on nutrient agar and potato dextrose agar to ensure there was no mould and bacterial growth.

Ten fish samples with weight ranges from 120-150 g each were selected for each of the four groups. The fish samples were headed gutted and cleaned with water. The first group was soaked in distilled water, while the second group was soaked in 2.5% clove solution, the third group was soaked in 2.5% ginger solution and the fourth group in a combination of 2.5% clove and ginger solution for three hours at ambient temperature (29-35°C). The samples were dried for 8-10 hrs a day for 5 days. The samples were submitted to microbiological, chemical and sensory scores following processing.

Microbiological analyses

Mould count: Three grams of the ground fish samples were mixed with 27 ml of sterile diluent and serially diluted. Using the pour plate method, the serial dilution were plated out using Potatoes dextrose agar (PDA) Saboroud Maltose agar and incubated for 5-7 days at 32° C (Harrigan and McCance, 1976; Collins and Lyne 1970).

Chemical analyses

The trimethylamine (TMA) values were measured by the AOAC (1984) method, while the free fatty acid (FFA) was determined using the method of Pearson (1981). The pH values were determined directly by using the pH probe (Negbenebor et al., 1995).

Sensory evaluation

A taste panel of ten members including staff and students of the University of Maiduguri rated the samples for color, texture, taste and overall acceptability based on a nine point hedonic scale with 9 representing "like extremely" and 1 representing "dislike extremely"(Amerine et al., 1965).

Statistical analyses

Data was subjected to analyses of variance (Steel and Torrie, 1980). Duncan's multiple range test and multiple F test ((Duncan, 1955) was used to separate the differences among the means.

3. RESULTS AND DISCUSSION

The initial mould count ranged from mean log 0.78 to 0.90 cfu/g for the treated samples as against 1.04 cfu/g for the non-treated controls (Table 1).

Table 1. The effect of clove and ginger on mean log mould count of solar-tent dried fish during storage

1 Each value is a mean of four determinations
2 Means in a row with unlike letters differ significantly (P<0.05)
FF=Fresh fish
SD=Solar dried
ND=Non-detectable

Samples treated with 2.5% clove and ginger separately had no detectable mould growth after two months of storage. Surprisingly samples treated with a combination of ginger and clove showed some evidence of mould growth suggesting that the combination has no synergistic effect. Mould rather than bacterial growth is the major problem in this type of product because of its low water activity (Negbenebor et al., 1995; FAO, 1992). The ability of the spices to inhibit mould growth would in a way enhance the over-all quality of the product.

Trimethylamine value

The trimethylamine (TMA) value of the fresh fish sample was 15.43 mg N/100 g. following processing the TMA values of the treated samples were significantly (P<0.05) lower than that of the non-treated controls, and remained so after 2 months of storage at ambient temperature (29-35°C) (Table 2).

Table 2. The effect of clove and ginger on trimethylamine value of solar-tent dried fish samples

1 Each value is a mean of four determinations
2 Means in a row with unlike letters differ significantly (P<0.05).

Results suggest that the spice inhibited the production of TMA from trimethylamine-oxide (TMAO) (Jay, 1987). However irrespective of treatment there was a decrease in TMA values of all samples after 2 months of storage at ambient environment. This may be related to the low RH and high temperature leading to the decrease in water activity, microbial activity and hence decrease in TMA values (Jay 19870). However after two months of storage there was little or no difference in TMA values of the treated samples.

Free fatty acids (ffa)

Following treatment the FFA values in the fresh fish ranged from 0.19-0.26% and was not significantly affected (P>0.05) by treatment (Table 3). However following solar-tent drying there was an inecrease in FFA values of all samples irrespective of treatment. However the control samples showed higher (P<0.05) FFA values when compared to the treated samples. Results suggest that the spices used in this experiment inhibit FFA production. The FFA content in a product is an indication of the quality of the product (Clucas and Ward, 1996).

Table 3. Effect of clove and ginger dip treatment on free fatty acid values of fresh and solar-tent dried fish (Clarias anguillaris)

1 Each value is a mean of four determinations
2 Means in a column with unlike letter differ significantly (P<0.05)

Sensory evaluation

The sample treated with 2.5% ginger was not significantly (P>0.05) rated higher than the control in terms of taste, colour, and texture (Table 4). However the samples treated with 2.5% clove was significantly rated higher (P<0.05) than the control in terms of taste, colour and texture but not in overall-acceptability. This might be due to the ability of clove to mask off- flavour and enhance the quality of the food (Purseglove et al., 1981).Such improvement in colour and taste would enhance the rate of turn-over of the product. The combined clove and ginger treated sample did not show any synergistic effect.

Table 4. Effect of clove and ginger treatment on sensory evaluation of solar-tent dried fish products

1 Means in a column with unlike letters differ significantly (P<0.05)

4. CONCLUSION

The dipping of fish in a mixture of ginger or clove before solar-tent drying have beneficial effects on the overall quality of the final products. This in a way will not only reduce the substantial losses associated with this type of product estimated at billions of nairas but would also increase the rate of turn over as consumers would now find increased satisfaction with the processed fish as indicated by the sensory quality of the product. This would substantially improve fish protein intake in Nigeria and reduce protein malnutrition and its associated problems in the country.

5. REFERENCES

AOAC (1984). Association of Official Analytical Chemists. Official Methods of Analysis 14^th Edition, Washington D.C

Adeniyi, J.P. (1987). Fish consumption in Nigeria. Implications for fishery development policies. J. West African Fisheries 3(2):151-161.

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Clucks, I.J. and Ward, A.R. (1996). Post harvest Fisheries Development: A guide to handling, preservation, processing and quality. Chamita Maritime, Kent ME4 4TB, U.K

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Duncan, D.B. (1955). Multiple range test and multiple F test. Biometrics 11:1-44

FAO. (1987). Simple methods of meat preservation. FAO paper No FAO, Rome, Italy.

FAO. (1992). Fermented fish in Africa. A study on processing, marketing and consumption. FAO Fisheries Tech. paper 329, FAO, Rome

Harrigan, W.F. and McCance, M.E. (1976). Laboratory Methods in Food and Dairy Microbiology. Academic Press, London.

Jay, J.M. (1987). Modern Food Microbiology. 3^rd Ed. EBS Publishers, New Delhi, India.

Kent, G. (1984). National fisheries policy of Thailand, FAO Fisheries circular No 777, FAO, Rome, Italy.

Negbenebor, C.A. (1990). Raw material supply for fish and animal processing Industries. In Proceedings of a workshop organized by the N/E Chapter of NIFST, Maiduguri, Nigeria. Pp12-24. Eds. I. Nkama and P. Sopade.

Negbenebor, C.A., Kaduara, S.G. Igene, J.O. and Chikwem, J. (1995). Preliminary studies in the production of "Bunyi- youri" (A putrefied sun-dried fish product). Agrosearch 1:25-33.

Pearson, D. (1981). Chemical Analysis of Foods. 8^th Ed. Pp 33-120. New York, Church-hill Livingstone.

Purseglove, J.W., Brown, E.G., Green, C.L. and Robbins, S.R. (1981). Spices, Longman, London.

Steel, R.G.D. and Torrie, J.H. (1980). Principles and procedures of Statistics. McGraw-Hill Book Co. Inc. New York.

Vileg, P. and Body, D.R. (1988). Lipid content and fatty acid composition of some New-Zealand fish. NZJ Marine Fresh water Res. 22:151.

Waterman, J.J. (1976). The production of dried fish. FAO fish report (F42), FAO, Rome.