Prediction And Control Of The Spoilage Of Fresh Cured And Dried Tropical Fish In Nigeria

Project and Seminar Material for Fishery and Aquaculture

Prediction And Control Of The Spoilage Of Fresh Cured And Dried Tropical Fish In Nigeria


The study of the losses in fish from Maiduguri, the North Eastern area of Nigeria between June and December, 2004 is reported. The study was carried out in two phases: (a) field work to determine losses by fish stakeholders (fishermen – fish processors – sellers) and (b) loss assessment in the laboratory to determine the rate of infestation with developmental stages of the major insect pest (Dermestes maculatus) which attacks smoked/ dried fish. The weights and proximate composition of the fish types at different moisture levels before and after insect attack, were measured. Loss estimates to the stakeholders were found to be between 28% – 36% of loss in number and biomass of fish per annum. Assessment over a period of thirty – two (32) days in the laboratory showed that the four fish species used in the study (Tilapia zilli (Mgbasa), Heterotis niloticus (Efi), Clarias gariepinus (Okpo) and Polypterus annectans (Ebiyi) with different moisture contents (15%, 20%, 25%, and 30%) showed varied losses. Higher oviposition was found in samples with the moisture levels 25% to 30% in all the fish species compared to15% and 20% moisture levels. The differences in oviposition levels were found to be significantly different (P < 0.05). The percentage mean weight losses observed after insect pest attacks in all the fish species were dependent on oviposition and fish composition. Proximate composition of the fish species showed no significant difference with fish moisture content before infestation but moisture content had significant effects after infestation. It is therefore concluded from these finding that Tilapia zilli was more susceptible to insect attacks than the other three (3) fish species. The study also shows that insect attacks on fish samples were more between 25% and 30% moisture levels than in the other moisture levels. It is therefore suggested that fish species should be smoked dried to lower moisture levels as 15-20% to avoid heavy insect infestation, and thus reduce losses due to insect infestation.

Chapter One


1.1 Background to the Study

Fish and seafood constitute an important food component for a large section of world population (Wafaa et al., 2011). They come after meat and poultry as staple animal protein foods where fish forms a cheap source of protein (Wafaa et al., 2011). Sea foods have traditionally being a popular part of the diet in many parts of the world and in some countries constituted the main supply of animal protein. Today, even more people are turning to fish as a healthy alternative to real meat (Adebayo-Tayo et al., 2012). Fish as an important food commodity in the international trade deteriorate rapidly especially when storage facilities are lacking. Fish is one of the most highly perishable food products (Sallam, 2007; Adebayo-Tayo et al., 2012).

Fish can spoil from both outer surface and inner surfaces as fish stomach contain digested and partially digested food which can pass into the intestine (Emikpe et al., 2011). After fish is being caught and dying the immune system collapses and bacteria are allowed to proliferate freely on the skin surface and the stomach (Emikpe et al., 2011). The walls of intestines do break down sufficiently for bacteria to move into the flesh through the muscle fibre. During handling and storage, quality deterioration of fresh fish rapidly occurs and limits the shelf life of the product (Sallam, 2007; Adebayo-Tayo et al., 2012). The quality of fish degrades, due to a complex process in which physical, chemical and microbiological forms of deterioration are implicated (Sallam, 2007; Adebayo-Tayo et al., 2012).

Fish spoilage is a complex process in which physical, chemical and microbiological mechanisms are implicated (Hozbor et al., 2006; Adebayo-Tayo et al., 2012). Spoilage is the result of a series of changes brought about in the dead fish mainly due to enzyme and bacterial action. It starts in the fish as soon as the fish dies when caught. In areas where temperature is high, fish spoil within 15-20 hours depending on the specie and the method of capture (Adedeji and Adetunji, 2004; Adedeji, 2012). Fish is extremely perishable. It spoils easily. “Spoilage” can be defined as a change in fish or fish products that renders them less acceptable, unacceptable or unsafe for human consumption.

Fish undergoing spoilage has one or more of the following signs: slime formation; discolouration; changes in texture; off-odours; off-flavours and gas production (Adedeji and Adetunji, 2004; Adedeji, 2012).
Preservation of fish is done to prevent spoilage. Since fish is very perishable, it is therefore, necessary to preserve fish if not consumed or disposed immediately (Adedeji and Adetunji, 2004; Adedeji, 2012). Fish preservation is the method of extending the shelf life of fish and other fishery products by applying the principles of chemistry, engineering and other branches of science in order to improve the quality of the products and control spoilage (Adedeji and Adetunji, 2004; Adedeji, 2012). Fish spoilage is mainly controlled by dehydration, lowering temperature, increasing temperature and using preservatives (Adedeji and Adetunji, 2004; Adedeji, 2012).

To control spoilage, one avoid exposing the fish to sunlight. Keep them in a shaded area. Ice the fish immediately after they are caught to lower their temperature (Adedeji and Adetunji, 2004; Adedeji, 2012). Remove the gills and internal organs. Avoid soaking the fish too long in the water after death as this easily spoils the fish. Use mechanical refrigeration if there are facilities (Adedeji and Adetunji, 2004; Adedeji, 2012). Salting, smoking, drying and cooking are among the methods used in control of spoilage in fresh fish while salting is majorly used in dry fishes. However, this study will examine approaches into the prediction and control of the spoilage of fresh cured and dried tropical fishes in Nigeria.

1.2 Statement of the Problem

Fresh fish is extremely perishable and is subject to bacterial spoilage. As fish spoils, its nutritional valuedecreases, as the bacteria causing the spoilage degrade the protein which is intended for human consumption. However, bacterial action produces nitrogenous compounds with noxious odours and the affected fish will become highly unattractive because there is too much nutritional damage. Bacterial spoilage in fresh fish can produce toxins which cause food poisoning; histamine contamination is prevalent among pelagic fish such as mackerel and sardine. Pathogenic bacterial contamination of fresh fish caused by poor handling and washing the fish in polluted water can also cause food poisoning. Traditional processing of cured fish frequently involves high temperatures, particularly when the fish is smoked or dried. It used to be thought that salting and drying effectively preserved the nutritional value of the original fresh fish and much of the older literature.

1.3 Objectives of the Study

The following are the objectives of this study:

  1. To examine the method of prediction of the spoilage of fresh cured and dried tropical fish in Nigeria.
  2. To examine the approaches for the control of the spoilage of fresh cured and dried tropical fish in Nigeria.
  3. To identify the disadvantages of fish spoilage.

1.4 Research Questions

  1. What is the method of prediction of the spoilage of fresh cured and dried tropical fish in Nigeria?
  2. What are the approaches for the control of the spoilage of fresh cured and dried tropical fish in Nigeria?
  3. What are the disadvantages of fish spoilage?

1.5 Significance of the Study

The following are the significance of this study:

  1. Finding from this study will educate on the method of prediction and control of the spoilage of fresh cured and dried tropical fish in Nigeria. The outcome of this study will also expose the factors causing spoilage in fish and the disadvantage of fish spoilage.
  2. This research will be a contribution to the body of literature in the area of the effect of personality trait on student’s academic performance, thereby constituting the empirical literature for future research in the subject area.

1.6 Scope / Limitations of the Study

This study will cover the approaches into the prediction and control of the spoilage of fresh cured and dried tropical fish in Nigeria.

Limitation Of Study
Financial constraint

Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet, questionnaire and interview).

Time constraint

The researcher will simultaneously engage in this study with other academic work. This consequently will cut down on the time devoted for the research work.

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Chapter Five

Conclusion and Recommendation

5.1 Conclusion

Fishes from Lake Chad suffers different types of losses before the processed or smoke dried fish reaches its final consumers. Losses recorded from the fish stakeholders – from the fishermen to the fish storage sites were about 28 – 36% loss per annum. This result agrees with the work done by Ladu et al (2001) who estimated losses at about 30-35% but in contrast with the works of Azeza 1976 and Osuji, 1976 which estimated losses to be about 40 – 60% mostly due to blowflies’ infestation, poor handlings, packaging, transportation and damage by rodents. From the study, the fresh fish is seen dumped by the fishermen on the ground or on raffia mats before and after they are washed. This exposes the fish to microbial infestation and encourages spoilage. The fish is also exposed to blowflies and houseflies which oviposit on them, maggots develop inside the fish which may aid the continuation of spoilage when eventually the fish is not properly smoke dried. Autolysis/spoilage sets in quickly in fresh fish, as a result, most fishermen in Lake Chad area keep their catches cool by keeping them under shades to reduce the temperature around the fish.

They ensure that the surface of the fish is moist and sometimes leave the fish covered in water as observed by Ezenwaji, (1997). According to the processors in Maiduguri and Doro-baga markets, it was clear that only small pelagic fishes such as Tilapia were sun-dried because they are lean and can dry fast. This process however exposes the product to blowflies and houseflies which oviposit on them causing spoilage thereby initiating loss. Sun drying is effective here mostly in the dry season and harmattan periods (Nov-March). They also confirmed that even in the rainy seasons, days without rain having high temperature and low humidity can be effective for sun-drying. Awachie and Ezenwaji (1981) had earlier reported that in Nigeria small pelagic fishes are dried using sun’s radiant energy as the only source of heat. They noted that fish are scattered or placed usually near inland river banks and especially in the northern states where abundant dry weather conditions are available. It was also observed in the markets that due to insufficient supply of woodfuel to smoke dry the product. The processors sometimes smoke the fish for a short time and display them in the sun on mats for the sun to further dry them. Okonkwo (1993) made this observation when he noted that most important fish products in Nigeria are smoked either partially or fully and spread in the sun for further drying in attempt to reduce cost of woodfuel used in smoking. The fishes are sometimes charred on heaps of grasses for lack of wood fuel as the fire cannot be well controlled which reduces the quality of the product thereby increasing losses.

It was further observed that the processors do not use salt or any form of preservative r fish before smoking. They only wash the fish and it goes straight to the smoking kiln, sometimes without gutting except for protepterus species. They believe this species contains a poisonous substance in its operculum. This situation suggests why most of the fishes which had already been attacked by blowflies or responding to autolytic spoilage continue to spoil even after smoking especially where smoking was not properly done. Osuji (1975) and FAO (1981) confirmed that insects and maggots attack on salted smoked fish was less compared to unsalted smoked fish. Azeza (1976) also reported that salting reduces the rate at which developmental stages/forms of beetle develop throughout storage period. The processors despite these, insists that the use of salt gives their fish a colour that is not palatable to their consumers thus they belief that salted fish fetch them less revenue and also reduces the time at which they would smoke a large number of fish. Azeza (1976) however reported that it was necessary to use the right quality and quantity of salt in order to avoid “pink” whilst producing an acceptable, palatable and tasty product.

When insects and rodents attack smoked fish, the products are prone to contamination with pathogens as numerous holes are created in them which predispose the product to fragmentation thereby reducing its volume, weight and nutritive value. Some of the fishes that have been attacked by insects and maggots are sometimes re-smoked to kill or drive out the organisms, thereby burning the products.

Smoking activities in these markets are usually carried out using locally constructed oven. They are designed with cylindrial metal drums with wire gauze shelves inside where the fishes are placed and a small opening beneath from where the wood-fuel is slotted inside the drum (plate 2a). This smoking device allows for smoking small quantity of fish. The fire can however be controlled and burning of the fish is reduced. The processors introduced another type of smoking kiln in order to smoke large quantities of fish. The kiln is constructed with mud and big wire gauze across it for placing fish with an opening on one side for wood-fuel (plate 2b). This method unknown to the processors allows for more losses as it is difficult to control the fire especially when smoking fatty fishes as oil drops into the fire to rekindle it resulting to fish burning. Okonkwo et al, (1991) had similar observation when they reported that such ovens made from local cheap materials, lack mechanisms of control of air circulation/smoke deposition, all of which affect the efficiency of smoking and the quality of the final product. They noted that because of the open nature of the ovens, energy utilization is poor and wasteful. There could also be incomplete combustion of wood leading to deposition of soot and resins on the products surface. These soot and resins constitute health hazards and lead to poor quality products which are usually dark and sometimes with sooty flavour (Okonkwo 1987).

The modern smoking kiln equipment used in this experiment has many advantages over the local smoking kiln used in the processing site.The modern smoking kiln is constructed with strong lron pans separted in-between with lron guaze where the fish is placed for drying away from the fire compartment unlike the local kiln made with mud and drums.The modern smoking kilns does not conduct much heat on its body as it is with the drum smoking kiln.This condition favours fish drying on the modern drying kiln as the fishes dries gradually because the fire is not directly close to the fish. There will also be little or no issue of case-hardening on the fish.The fishes smoke dried with the modern smoking kiln will not decay easily by means of fungi or mucor on the fish as the fish dries well on the inside,only containing the required moisture level unlike the local kiln with little orno regulation/control. There may be no need for re-smoking the big fishes because of early decay as this the case with the local smoking kilns.

It was observed in the study area that fragmentation/breakage was a major problem as various heaps of broken fishes were seen displayed for sale. On investigation it was observed that this situation was caused by many factors such as over drying of the fish. Such over dried fish breaks easily during packaging for transportation. Smoking already spoilt fish and nonchalant attitude exhibited by people loading the fish unto lorries was another factor.

Ezenwaji (1997) observed that fish processed after full fermentation was more brittle and liable to easy fragmentation. He further noted that fish species with very soft flesh produce very fragile dried products which tend to break easily during handling and transportation. From the study it can be suggested that fishes should not be over-dried and not allowed to ferment before smoking. This can be achieved by the processors buying the quantity of fish they can handle a day depending on the number of smoking kilns available. Fish smoking should not be delayed after purchase.

It was observed in the markets that the predominant packaging material was carton (plate 3). From the nature of the packaging however, it may be suspected that it might not be able to offer adequate protection against insect attack. It might not be able to protect the product against physical damage during transportation as the material is not strong enough especially when they are heaped on top of one another during transportation. Open topped lorries are however, in common use and little attempt is made to protect the fish from the weather as was observed earlier by Osuji (1976).

In the storage sites it was observed that spoilage of smoked fish storaged for about 4 – 10 days is due to oxidative breakdown of fats with the production of off colours on the fish. Ezenwaji (1997) also reported that oxidative rancidity does not depend on moisture content alone but on the presence of molecular oxygen. He suggested that this can be prevented by the exclusion of air (oxygen) where the fish is kept by using air-tight containers to package and store fish. Unfortunately, this is not practicable in Nigeria for smoked fish due to low technological advancement of the country. However, he noted that when introduced, it can help in prolonging the shelf life of smoked fish by also preventing other spoilage activities as insect infestation. It was observed that smoked fish absorbs moisture on prolonged storage or during periods of high relative humidity as in the rainy seasons. This situation can lead to swelling of the fish and mould growth which can initiate easy breakage. Proper drying/smoking can control this situation. Ezenwaji (1997) suggested that moisture absorption can be prevented by using moisture proof packaging, the best of which is air-tight tins. This technology however might not be feasible in Nigeria partly due to poverty, illiteracy or even ignorance. He therefore recommended packaging materials like thick polythene bags available in the country and cheap to obtain. Polythene bags however can be easily torn by fish spines thereby providing access to insects. The polythene bag also can release moisture inside making the fish surface wet and conducive for mould growth. He further suggested that to prevent moisture inside the polythene bag, the package must be kept under cool environment i.e. avoiding direct sunlight and in rooms with temperature differentials.

In all the fish samples examined pre-oviposition periods varied greatly (P<0.05). In T. zilli the longer preoviposition period was in 15% moisture level. This low moisture level in T. zilli probably prohibited oviposition by the beetles (Ezenwaji and Obayi 2004). The oviposition period was however shortest for this level. H. niloticus and C gariepinus showed an inverse relationship to the above observation as the longer preoviposition periods were in their 30% moisture level thus, the higher the moisture level the longer the preoviposition period. P annectans showed a total difference as its 25% moisture level exhibited a shorter preoviposition time and the longest oviposition time. Generally oviposition time was shortest in T. zilli and longest in P. annectans and there was no significant statistical difference between H niloticus and C gariepinus. Oviposition (number of eggs laid) increased in all the fish samples as moisture levels increased and also reduced as moisture level decreased showing that oviposition is moisture dependent. This observation probably explains the observation made by Johnson and Esser (2000) that fish with moisture level of 32% – 47% are very suitable for infestation with dermestid eggs.The fecundity of D maculatus females (27.7 – 353.3) is in conformity with the works done by Taylor, (1964, 160 eggs; Osuji, (1985, 250 eggs) and Michael, (2000, 318 eggs).

There is a strong inverse relationship between the number of eggs laid in these fishes sampled and the percentage rate of hatching of eggs into larva as moisture level increased. This observation confirms the report by Ezenwaji and Obayi (2004) which showed that at 14% moisture content 54 eggs were laid by the C.gariepinus and 43 (79.63%) larva observed while at 77% moisture content 598 eggs were laid hatching into 120 (20.07%) larva.

Pupae development was extremely low compared to the high rate of larval percentage survival. Pupae emergence showed inverse relationship with moisture level and direct relationship with larval development as the higher the percentage larval developments.

Emergence of adult D maculatus was very high and varied greatly independent of both moisture level and percentage rate of pupal developments.

An overview shows that D maculatus developmental stages survived more in lower moisture levels (15%, 20%) than in the higher moisture levels (25%, 30%). For fish samples, survival rate was much higher in T. zilli and lowest in P annectans with no significant difference between H niloticus and C gariepinus.

Percentage mean weight loss after infestation in the fish samples examined was highest in T.zilli and lowest in P. annectans showing direct relationship with oviposition. This observation is independent of moisture levels since the weights of the fish samples before insect infestation was not significantly different. This observation suggests that D maculatus females fed more on T. zilli than the other fishes. This can however be attributed to its low fat content. Percentage moisture loss in all the fish samples were higher in P. annectans and H. niloticus than in T. zilli and C gariepinus. Percentage moisture loss was dependent on the initial moisture contents of the fish samples as 30% moisture level had high percentage moisture loss.

The protein composition of all the fish samples at different moisture levels varied (P < 0.05). This observation compares favourably with that reported by Ikeme (1991) where proximate composition of smoked dried fish samples were taken from production sites and the market. In all the fish samples T.zilli contained the highest value of protein followed closely by Clarias gariepinus. After infestation the protein contents of the fish samples readily increased. This is attributable to concentration effect due to moisture loss. The fat contents of all the fish samples were in contrast with the earlier work done by Ikeme (1991). However P.annectans contained the highest fat level while T .zilli had much lower fat contents. The pest,dermestes used to infest the fishes influences increase in fat content of the fish in that the pest consumes the fishes which contain fat ,extracting the fat from the fish body into its body. On excreation by the pest,their waste product will contain the fat from the fish.The waste therefore increases the fat content in the fish after analysis as the waste products were not sieved off before analysis. The ash contents did not vary greatly (P>0.05). The observation made however was all smaller than the reports of earlier works. After infestation the observation increased similar to other proximate composition results also attributable to concentration effects due to moisture loss. P.annectans however recorded the lowest result while Clarias had the highest in contrast with Ikeme (1991). There was no significant difference between T. zilli and C. gariepinus in their ash contents.

The fibre contents of all the fish samples were all in the same range before infestation.

After infestation P.annectans showed the lowest content of fibre. The carbohydrate contents of all the fishes varied. P.annectans however had the highest carbohydrate content both before and after insect pest infestation.

An overview shows that proximate composition of fish samples were not dependent on moisture contents of fish samples before infestation but rather on types while all values increased after infestation due to moisture loss. The effect of long pre-oviposition period on the life of an insect is the probability of the insect having a low life expectancy by the time its set egg laying thereby laying few eggs.Survival rate of the insect will be low as its lays fewer eggs which may likely have a low survival rate as it undergoes metamorphosis.

Short pre-oviposition period encourages laying of plenty eggs by the insect thereby increasing its life expectancy and survival rate.The survival rate of the different stages of the insect will also be high thereby producing more adult insects so the abundance of the insect.

Long oviposition period in the life of an insect entails laying of plenty eggs thereby increasing the insects survival rate as it passes through complete metamorphosis. This condition also favours higher life span of the female insect; for the female insect might not die as agravid female.

Short oviposition period in an insects life on the other hand favours laying of few eggs thereby reducing the survival rate of the insect as the egg passes through complete metamorphosis. The life span of the female insect also reduces as the gravid female may likely die after oviposition.

5.2 Recommendations

Majority of the fish stakeholders are illiterates and they are also ignorant of modern devices/ methods used in fish handling. These stakeholders should be educated at least to adopt modern methods in their trade and maintain good hygienic practices. This can be achieved by fishery research institutes embarking on education programmes for them in their fishing ports/communities and markets. This will reduce losses and increase quality and quantity of product which will attract higher income to these stakeholders.

Basic infrastructure and modern smoking kilns should be provided in these fishing communities which are less time consuming and labour effective reducing the time the fish will stand before smoking. This will eventually reduce spoilage/autolysis thereby reducing a greater percentage of loss.

Loss assessment studies are not always straight as there are variations involved with season and different geographical locations. A six month observation carried out in this study may not be sufficient to ascertain losses in this area as there may be great difference between one season and the other and between one year and the next. Finance however is a great constrain for a self-financed researcher. Improvement in this aspect therefore can be achieved if the government through fishery research institutes or individual researchers finances these projects for at least minimum of five years period in different fishing locations in the country to actually measure loses so as to effectively recommend solutions.

The cost of laboratory studies are too high so the need to study few fish species for a self-financed researcher. All the dominant fish species/types in a study area chosen should all be studied to effectively recommend the type/fish species which can effectively resist insect infestation and at what conditions to effectively combat these problem of losses. It is however recommended from this research work that drying fish to lower moisture levels as 15%-20% can help reduce losses.

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