Food and feeding habits of Crucian carp (Carassius carassius) in Melkawakena Reservoir, Ethiopia

Lemma Abera Hirpo

Zwai Fishery Research Center
P.O.Box 229, Zwai, Ethiopia
negrofarm@yahoo.com

Abstract

Food and feeding habits of Carassius carassius in Melkawakena reservoir were studied. Samples of C. carassius were collected monthly during August (2009) through to July (2010) using gillnets of different mesh sizes.

C. carassius was found to ingest a variety of organisms of plant and animal origins, as well as items including detritus and sand grains. However, insects, zooplankton and phytoplankton were found to be the most important food of the fish in the reservoir. Thus, the fish is considered to have a mainly omnivorous feeding habit. The major food items ingested were insects when the size of the fish is increase. However, the importance of phytoplankton and zooplankton tended to decrease where as that of insect tended to increase with the length of C. carassius. Thus, it appeared that the fish feeds progressively more insect as it grows larger. High incidence of empty stomachs was observed during the whole sampling period. But, the frequency of empty stomach was high during the rainy season, which could be associated with breeding activity.

Key Words: Fish, food items, periodicity, stomach content

Introduction

The study of interactions between the links in complex food chains can lead to an understanding of how specific organisms gain their food sources. Many components constitute these intricate food chains, from the smallest micro organisms, to the largest fish species; these all have consequential roles when assessing the ecological stability of a body of water. To advance the knowledge of feeding preferences of any one particular species, an understanding of the broader aquatic community is a requisite.

In freshwater fisheries management and aquaculture, the evaluation of natural food biomass is of importance, as in many cases, this is the primary source of food; sometimes the addition of artificial feeds are used as supplements. To gain equilibrium between the feeding of natural and artificial food, careful monitoring must be undertaken; this is essential due to the variability created by natural conditions. Just as significant is gaining an idea of the most utilised, most easiest obtainable and highest calorific value organisms as these all aid the development and growth rate of the species further up the food chain.

Since, the apparent abundance of C. carassius accumulated within Melkawakena reservoir. Nevertheless, scientific knowledge on the fish food and feeding habits in the reservoir is limited. Hence, this information provides baseline information that useful for sustainable exploitation and management of fisheries in the fish in the reservoir.

Materials and methods

Field sampling and measurement

Samples of C. carassius were collected monthly between August 2009 and July 2010 using gill nets from different sites. The gear were set in the afternoon (05:00 pm) and lifted in the following morning (7.00 am). Then immediately after capture, fork length (FL) of each specimen was measured to the nearest 0.1 cm. The stomach was checked if it contained any food. If it was empty, this was recorded, whereas stomach with contents was preserved in 5% formaldehyde solution. Preserved samples were then transported for further laboratory analysis. 

Stomach content analysis

Preserved content of each stomach was transferred in to petri dishes. Larger food items were identified by eye, whereas small sized food items were microscopically examined using a WILD type stereoscope (magnification 6X to 50X), and each food item was identified to the lowest taxon possible using description, illustrations and keys in the literature (Defaye 1988). In addition, smaller food items, such as phytoplankton, were examined at high magnifications (100X to 400X) under a compound research microscope. After identification, a list of items found in the stomach content was prepared, and each item counted whenever appropriate. Counting was performed using the whole stomach content for the majority of the samples. In some cases, however, counting was done from a sub-sample of 10 ml stomach content. All counts were converted to number per total volume of stomach content.

Determination of relative importance of food items

The relative importance and contribution of each food item to the diet of C. carassius was determined using the standard methods, i.e., the frequency of occurrence method and percent composition by number (the numerical analysis) (Hyslop 1980).

Estimation of fish size and feeding habit relationship  

To study whether there is ontogenetic shift in the food habit of C. carassius, results from each method were plotted against length of fish. Food items were grouped into major taxonomic groups for this purpose.

Estimation of feeding periodicity 

Seasonal difference in food habit of C. carassius was studied from the frequency of empty stomachs, and also from results on relative contribution of major items as determined from frequency of occurrence, and   numerical abundance methods.

Result and discussion

Stomach contents

A total of 789 stomach samples of fish varying in length between 7 and 36 cm FL were examined for food composition study. Of these 386 (49%) were completely empty. The list of items observed in the stomach contents of the fish is presented in Table 1. C.carassius in Melekawakena reservoir ingests a variety of organisms and items. Organisms identified from the stomach contents of the fish varied from plankton to higher plants (Macrophyta) (Table 1). These organisms are also ingested by the same species in other countries in different water bodies reported that in the stomach content of similar fish spices different algae, rotifers, cladocerans, copepods and insect larvae identified.

Relative importance of major food items

Frequency of occurrence

Organisms that were found relatively more frequently were insects, zooplankton and phytoplankton. Of these, the majority of C. carassius (79.8%) frequently ingested different groups of insects. The next important food items, which were ingested by most fish, were zooplankton (62.4 %) and phytoplanktons were 44.1, 42.1 and 13.8 for Diatoms, Blue green and Green algae respectively. Macrophytes (55.88 %) and detritus (9.2 %) were also recorded in the stomach of the fish (Table 2 and 3). 

The high frequency of insects was mainly due to Diptera (72.3 %) and Hemiptera (59.6 %) and most of the percentage frequencies of the other insects were below 14 %. The frequency of zooplankton was lower than that of insects, and the highest frequency was for Rotifers (57.1%) (Table 3). On average, therefore, insects were the most frequent food in the diet of C. carassius in Melekawakena reservoir.

Numerical abundance

Based on percentage composition by number, zooplankton was the most important diet of C. carassius in Melkawakena reservoir, which contributed 88.17% of the total food ingested (Table 3). Rotifers, Copepoda and Cladocera contributed 79.12% and 47.5% and 6.7 respectively, of the total food counted (Table 3). Similarly in other study Zooplanktonic organisms are proven to be significant natural food sources of carp resulting in many scientific investigations involving these organisms.

Among insect groups Odonata, Diptera and Hemiptera contributed each about 0.19 to 1%. The remaining insects were each less than 0.13 % of the total number of food items encountered in the stomach content of C. carassius (Table 3). The remaining item like macrophyte tissues and detritus were also observed frequently in the diet but, as it was difficult to count them, could not be compared numerically. In general, insects, zooplankton and phytoplankton each as a group contributed to the bulk of the diet, and they were the most important food of C. carassius in the reservoir.

Fish size and feeding habit relationship

The relationship between size of C. carassius and its feeding habit, which was studied based on the frequency of major food items (insect, zooplankton and phytoplankton), is shown in Figure 1. The major food items were ingested by individuals belonging to all length classes ranging from 7 cm to 36 cm of FL. The feeding habits of the fish composed of all food items, but the bulk of the food of C. carassius below 16 cm FL was composed of phytoplankton and between 17 to 26 cm was composed of zooplankton, whereas for larger fish the frequencies of the insect items were more. Generally, however, frequency of occurrence tended to increase for insect, whereas it tended to decrease for phytoplankton with increase in FL of C. carassius (Fig.1). 

Figure 1. Relationship between fork length of C. carassius and its food habit based on frequency of occurrence method

Feeding periodicity

Fish with empty stomachs, which accounted for about 49% of the total, occurred in all sampling months, but they were more frequent in August  (80 %),  September (70%), April (65%) and (60%) for March and July each. The frequency was the lowest in January (25 %) (Fig.2).

Figure 2. Frequency of C. carassius with empty stomach from the reservoir.

High incidence of empty stomachs was observed during the whole sampling period. But, the frequency of empty stomachs was high during the rainy season, which seems to be associated with breeding activity. As mentioned earlier heavy rainfall and subsequent rise in water level trigger spawning of most fish spices in African water bodies (Willoughby and Tweddel 1978) including Lake Tana (Tesfaye Wudneh 1998), Awassa (Elias Dadebo 2000) , Langeno (Leul Teka 2001) and Zwai (Daba Tugie and Meseret Taye 2004) in Ethiopia. Thus, the fish may be engaged more in spawning activity than in feeding.

Figure 3. Seasonal fluctuation in frequency of occurrence of major food items of C.carassius from the reservoir

The contribution of insects and zooplankton was relatively highest during late rainy season, whereas the contribution of phytoplankton to the diet of the fish was relatively less (Fig.3). The seasonal variation in food habit could be due to the opportunistic nature of the fish, which is capable of shifting from one diet to another depending on temporal variations in availability of the diet in the lake (Fryer and Iles 1972; Philipart and Ruwet 1982; Matipe and De Silva 1985). The same has been concluded for other species in L. Awassa (Elias Dadebo 1988, 2000), L. Langeno (Leul Teka 2001) and L. Zwai (Daba Tugie and Meseret Taye 2004).

Conclusions

• This study has explored the aquatic interactions between the micro and macro-organoisms and the fish within Melkawakena reservoir and has resulted in knowledge of the C.carassius feeding habits and preferences. Since, the study is the first of its kind to be conducted on C.carassius in Melkawakena reservoir. Therefore, further detailed studies are required on other aspects of the fish, as well as identification of appropriate gears for the fish in particular. However, some conclusions and recommendations can be made based on the findings of the present study. First, proper management actions are required to protect the immature fish. Therefore, gear size and type must be recommended for the fish in the reservoir. Secondly, C.carassius in the reservoir was found to feed mainly on phytoplankton, zooplankton and various developmental stages of insects. Therefore, conservation and management plan considering to protect these natural food of the fish would be an important development. Third, prior to this, however, in addition to the studies mentioned above, stock assessment study is strongly recommended to estimate optimum fishing level and sustainable yield.

References

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Received 24 April 2012; Accepted 24 May 2012; Published 1 June 2012

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