The Food and Feeding Habits of Fish Species Assemblage in a Niger Delta Mangrove Creek, Nigeria

INTRODUCTION

The extensive Niger Delta mangrove (over one million hectare) is the largest in Africa (Spalding et al., 1997) with diverse fish resources. The mangrove and its diverse fish resources are fast being depleted due to uncontrolled anthropogenic activities. There have been warnings, that supportive data have not been collected and that fish and decapods use of mangrove may not be the same in all areas of the globe (Chong et al., 1990).

Adult fishes feed in a variety of ways, ranging from sieving phytoplankton or grazing algae, to suction feeding on benthic invertebrates and to devouring other fishes whole or in portions (Bone et al., 2004). There is paucity of information on the food and feeding of fish species assemblage of Nigerian coastal waters. The food and feeding interrelationship of the fishes occurring in Lagos lagoon have been discussed, Fagade (1971) reported that two common species Tilapia melanotheron and Tilapia guineensis fed on similar food items, algae filaments diatoms and unidentified organic matter; Fagade and Olaniyan (1972) found that Ethmalosa fimbriata fimbriata fed on phytoplankton, zooplankton and unidentified food; Fagade and Olaniyan (1973) found that food of Lagos Lagoon fishes covers a wide spectrum and most of the available invertebrates are being utilized as food by the fishes. They defined fishes feeding on macroscopic animals as predatory species while those whose food include much bottom deposit (detritus) are called bottom or deposit feeders. They further grouped predatory species into piscivorous species i.e, fishes found feeding principally on fishes and non- piscivorous species, those fishes feeding more on other macroscopic animals other than fishes. They concluded that the division is not water-tight as some over-lapping exists. In the Niger Delta, Odum and Anuta (2001) reported that the main food items of Phractolamus ansorgii from Warri River were detritus, algae and sand grains and that the fish fed more actively in the dry season while diet diversity decreased with increased size. Alfred-Ockiya (2000) examined the found habits of goby, Porogobius schelgelii from the artisanal fisheries of the Bonny River in the Niger Delta and reported that they are omnivores, with detritus, diatoms and blue-green algae being the primary food items, followed by sand granules, macrophytes and nematodes as secondary food items. Stomach content has been used by many investigators to establish the food habits of fishes (Hartley, 1948; Hynes, 1950; Ball, 1961; Corbet, 1961; Munro, 1967). In fishes with no well-defined stomach, the contents of the entire gut were analysed (Corbet, 1961). Olaniyan (1969) suggested salinity as an important ecological factor in the distribution of fish fauna in the Lagos Lagoon. Fagade and Olaniyan (1973) posited that the availability of the food of the fish species can also influence their distribution. Wright (1986) attributed salinity to be the most important factor affecting fish population in shallow water creeks of a Nigerian mangrove swamp. Little et al. (1988), attributed high species record in East African mangrove creeks to the constant high salinity (approximately 35%) measured throughout the study period.

Although Oribhabor and Adisa-Bolanta (2009) have reported the food and feeding of tilapia species in Buguma Creek, Nigeria, this work which is the sixth in a series to provide data on the biology and ecology of fish species of the creek, is the first to document the food and feeding habits of the fish community of the creek and any Niger Delta mangrove creek.

MATERIALS AND METHODS

The Buguma Creek is located southeast of the Niger Delta between longitude 6°47'E and 6°59'N and latitude 4°36'N and 4°59'N Fig. 1. Detailed description of the three fish sampling stations have been given by Oribhabor and Ogbeibu (2010).

The fish samples collected monthly from November, 2004 to June 2006 at flood tides were caught by the use of hooks and lines and cast nets. The fish samples collected from three stations were ice-packed, kept chilled under ice-blocks in a plastic cooler and immediately transported to the laboratory. In the laboratory, fish specimens were pooled, sorted and identified to species level using the keys and descriptions of Scheider (1990) and Olaosebikan and Raji (1998).

The gut of each specimen was removed and preserved in a specimen bottle containing 4% formaldehyde. Each stomach was cut open and the contents washed into a petri dish using 4% formaldehyde. The food items were identified to the least taxon possible and counted. The frequency of occurrence, numerical and fullness methods (Hynes, 1950; Bagenal, 1978; Ogbeibu and Ezeunara, 2002) were used for analyzing the food items.


Fig. 1:	Map of the study area: (A) Nigeria showing Niger Delta, (B) Rivers state showing Buguma and (C) The study creek showing fish sampling stations

Table 1:	Filled portion of stomachs in buguma creek fishes, Nov. 2004-June. 2006

RESULTS

The species were arranged according to families and similarity of food items found in their stomachs. The results of analysis of stomach contents using the fullness method are shown in Table 1 of the 1149 specimens examined, 299 (26%) were empty stomachs. 150 (13.1%) were fully loaded stomach while 222 (19.3%), 275 (23.9%) and 203 (17.7%) were, ¾, ½ and ¼, respectively. Among the fishes represented by a single specimen, only Gobius sp. had empty stomach. Two of the remaining five species, Elops lacerta and Liza facipinnis had fully loaded stomachs while Sphyraena guachancho, Sphyraena sphyraena and Cynoglossus senegalensis had their stomachs half full Table 1.

The results of stomach content analysis using the frequency of occurrence method were based on all the species present except for Gobius sp. that had a single representation and also had empty stomach Table 2-8. Numerical method was used for all the species, except for L. falcipinnis, M. cephalus and Gobius sp. Table 2-8. Analysis of stomach contents of the fishes, E. lacerta, A. gigas, E. aeneus, C. latus, L. agennes, L. goreensis, P. macrolepsis, P. jubelini, A. regius, Pseudotolithus senegalensis, Fonticulus elongatus, P. sebae, S. afra, S. guachancho, S. sphyraena, P. quadrifilis, T. lepturus, C. senegalensis and D. margarita indicate that predatory fishes dominate the species, although some were found to have stomachs containing unidentified plant parts, unidentified fruit seed, dead plant matter while others were bottom (detritus) feeders.

Table 2:	Analysis of Food Item Found in the Stomachs of Elops lacerta, Arius gigas and Epinephelus aeneus in the Study Area, Nov. 2004- June 2006

%0: Percentage of occurrence, %N: Percentage of number

Animal preys which dominated the stomach contents of the dominant predatory fishes based on results of both the occurrence and numerical abundance methods were Insects, Shrimps, Lobsters, Crabs, Fishes, Polychaetes, amphipods, isopods, pagurid decapod, molluscs and nematodes.

Table 3:	Analysis of food items found in the stomachs of Caranx lactus, Lutjanus agennes and Lutjanus goreensis in the study area, Nov. 2004-June 2006

%0: Percentage ofoccurrence, %N: Percentage of number

Other items found in the stomachs of some species were pebbles in P. jubelini, A. regius, P. senegalensis, P. elongatus and D. margarita; sand in D. margarita and mud in P. jubelini, P. sebae and D. margarita.

Shrimps species, represented by Glyphus marsupialis, Nematopalaemon hastatus, Parapenaeus longirostris, Penaeus notialis and Sicyonia sp. constituted the dominant food items among the food species. They dominated the food items o f E. lacerta Table 2, C. latus and Lutjanus goreenis (Table 3), P. jubelini (Table 4), A. regius, Fonticulus elongatus, Pseudotolithus senegalensis (Table 5).

P. guadrifilis and T. lepturus (Table 7) by both the occurrence and numerical abundance. They occurred either partially as whole juvenile, parts or partially digested form or in mysis form for N. hastatus and P. longirostris.

Table 4:	Analysis of Food Items Found in the Stomachs of Plectorhynchus macrolepsis and Pomadasys jubelini in the Study Area, Nov. 2004-June 2006

%0: Percentage ofoccurrence, %N: Percentage of number

P. longirostris mysis occurred in A. gigas Table 2, Fonticulus elongatus and T. lepturus while N. hastatus mysis occurred in Fonticulus elongatus, Pseudotolithus senegalensis, P. quadrifilis and T. lepturus. These mysis forms are planktonic while the juvenile forms and adults are benthic. Penaeus notialis were scanty and were found in only A. regius and L. goreensis. Sicyonia sp. was found only as a single individual in S. melanotheron (Table 8).

Table 5:	Analysis of food items found in the Stomachs of Argyrosomus regius, Pseudotolithus (Pseudotolithus) senegalensis and Pseudotolithus (Fonticulus) elongatus in the study area, Nov. 2004-June 2006

%0: Percentage ofoccurrence, %N: Percentage of number

The Lobster, Scyllarides herklotsii was another food item which was always found in the stomach contents of A. gigas, L. goreenis, P. macrolepsis, P. jubelini, A. regius, Fonticulus elongatus, Pseudotolithus senegalensis and P. quadrifilis, particularly at times when shrimps were scarce.

True Crabs, represented by the dominant Geryon maritae, Goniospsis pelii, Sesarma angolense and Callinectes marginatus occurring as larvae, juveniles, parts or partially digested form, constituted the dominant food items of Arius gigas (Table 2) by the occurrence method. They also occurred in the stomach contents of L. agennes, E. aeneus, P. macrolepsis, P. jubelini, A. regius, Fonticulus elongatus. Pseudotolithus senegalensis, P. quadrifilis, D. margarita and S. melanotheron.

Extraneous insects, wing reproductive termite, Termes flavipes which occurred in the water at a period of nuptial flight was found in large number in the stomach content of A. gigas (Table 2) and P. sebae (Table 6). Extraneous hymenopteran nymph was also found in the stomach content of S. melanotheron (Table 8). Diptera larvae, represented by Chironomus transvalensis, Cryptochiromomus sp. Polypedilum sp. and Palpomyia sp. dominated the stomach content of P. macrolepsis (Table 4). The Trichopteran, Oxyethira sp. was also found in the stomach content of Sarotherodon melanotheron.

Isopods (Gnorimosphaeroma sp. and Ligia sp.) and nematodes dominated the food items of D. margarita Table 7. Gnorimosphaeroma sp. and Ligia sp. were also found in Fonticulus elongatus. Nematodes which were most abundant in Fonticulus elongatus were also found in A. gigas, E. aeneus, C. latus, P. macrolepsis, P. jubelini, Pseudotolithus senegalensis, P. sebae, S. afra, P. quadrafilis, T. lepturus and D. margarita. Amphipods, represented by Argissa and Ampelisca brevicornis were also found in Fonticulus elongatus. Also found in Fonticulus elongatus was the pagurid decapod, Clibernarius sp. (Hermit Crab) (Table 5).

Table 6:	Analysis of Food Items Found in the Stomachs Of Psettias sebae, Sphyraena afra, Sphyraena guachancho and Sphyraena sphyraena in the Study Area, Nov. 2004-June 2006

%0: Percentage ofoccurrence, %N: Percentage of number

Table 7:	Analysis of food items found in the stomachs of Polydactylus quadrifilis, Trichiurus lepturus, Cynoglossus senegalensis and Dasyatis margarita in the study area, Nov. 2004 -June 2006

%0: Percentage ofoccurrence, %N: Percentage of number

Table 8:	Analysis of food items found in the Stomachs of Sarotherodon melanotheron, Tilapia guineensis, Liza falcipinnis, Mugil cephalus and Mugil curema in the study area, Nov.2004-June. 2006

%0: Percentage ofoccurrence, %N: Percentage of number

Polychaetes in partially digested form were found in Arius gigas. The species, Harmothoe sp. was found in Pomadasys jubelini Table 4. Molluscs represented by Tympanotonus fuscatus fuscatus and Tympanotonus fuscatus radula were found in the stomach contents of E. aeneus and L. agennes. The planktonic Crucibranchaea sp. was found in Polydactylus quadrafilis. Unidentified shell parts were found in D. margarita.

Unidentified animal parts were found in E. aeneus, P. quadrifilis, L. agennes, L. goreenis, P. jubelini, P. macrolepsis, P. elongatus and M. curema.

Unidentified plants parts were found in A. gigas, C. senegalensis, P. sebae, L. agennes, L. goreensis, Fonticulus elongatus, Pseudotolithus senegalensis, P. macrolepsis, E. aeneus and P. jubelini. Dead plant matter was also found in P. sebae and Fonticulus elongatus. Unidentified fruit seeds were found in S. melanotheron. Pebbles were found in P. jubelini, A. regius, Fonticulus elongatus, Pseudotolithus senegalensis and D. margarita. Sand was also found in D. margarita.

Mud was found in P. jubelini, P. sebae and D. margarita. Mud was the dominant food item in the stomach contents of the bottom feeders, S. melanotheron, T. guineensis, L. falcipinnis, M. cephalus and M. curema.

A. gigas, Fonticulus elongatus, Pseudotolithus senegalensis, T. lepturus, P. quadrifilis, S. afra, S. guachancho and S. sphyraena were benthopelagic feeders while C. latus, C. senegalensis, D. margarita, E. lacerta, P. macrolepsis, P. jubelini, L. agennes, L. goreensis, P. sebae, A. regius and E. aeneus were benthic feeders and all were predominantly predatory.

DISCUSSION

The food items in the stomachs of Buguma creek fish species indicated that they were euryphagous, i.e., feeding on a wide range of organisms (Olojo et al., 2003), except for bottom feeders in the families Cichlidae (S. melanotheron and T. guineesis) and Mugilidae (L. falcipinnis, M. cephalus and M. curema). The food of the predatory feeders were highly dominated by benthic and planktonic species.

Any seasonal changes in the composition of the stomach contents probably reflected the abundance and availability of each item recorded (Beumer, 1978).

Comparison with finding of Fagade and Olaniyan (1973) on Lagos lagoon species reveals a minor shift in food items. M. sebae, L. goreensis, P. elongatus and P. jubelini which they considered non-piscivorous predators in their study were found to be piscivorous predators in this study. This could be attributed to differences in habitats, relative abundance of prey organism and individual species food habitat (Sarker et al., 1980; Alfred-Ockiya, 2000). But their finding that E. lacerta, E. aeneus, C. hippos, Sphyraena spp. and P. quadrifilis are piscivorous predators conforms with this study. Other piscivorous predators in this study were L. agennes in which whole Sardinella maderensis and fish parts were found, Pseudotolithus senegalensis and A. regius.

Apart from the bottom feeders and the piscivorous Sphyraena spp., the overall picture of the diet that emerged from the fishes of Buguma Creek is that of species which are largely unspecialised in their feeding habits. This is further confirmed by the feeding on the extraneous wing reproductive termites, Termes flavipes by A. gigas and the extraneous hymenopteran nymph by S. melanotheron. Unspecialised flexible dietary habits are an optimal strategy for survival in habitats where food sources are subject to fluctuation (Welcomme, 1979; Olojo et al., 2003). Similarly, the inclusion of large amount of mud (detritus) in the diet of D. margarita (Dasyatidae) is of survival value. It is abundant always in the creek.

Shrimps juveniles and mysis were the dominant food items of the predatory fishes. The abundance of these shrimps could be attributed to the fact that unlike penaeid adults that live offshore and spawn in deeper waters, the juvenile forms inhabit estuaries (Khan et al., 2001). The predators also feed on the lobster, Scyllarides herklotsii. This serves as dominant food item at periods when shrimps were not available.

The occurrence of the planktonic Shrimp mysis in the diet of A. gigas, Fonticulus elongatus, Pseudotolithus senegalensis, T. lepturus and P. quadrifilis which was also observed to feed on the planktonic Crucibranchaea sp. is an indication that they are benthopelagic. The predatory fishes of Buguma creek were either benthopelagic or benthic feeders.

Stomach content analysis based on fullness method revealed that out of 1149 number of fishes examined, only 299(26%) had empty stomach. This could be attributed to the fact that predatory fishes have irregular feeding habit and tend to take a large meal when their prey is available (Corbet, 1961; Thomas, 1966; Munro, 1967; Fagade and Olaniyan, 1973). Odum and Anuta (2001) attributed high empty stomach in Phractolaemus ansogii to intermittent feeding. On the other hand, the mud containing detritus was always available for the bottom feeders.

Frequency of occurrence method was not used for Gobius sp. because only one individual was examined. The numerical method was not used for L. falcipinnis, M. cephalus and T. giuneensis because only mud was found in their stomachs.

ACKNOWLEDGMENTS

We are grateful too Dr. Ezenwa, B.I. and Mr. Ugbodu, V.A. of Nigerian Institute for Oceanography and Marine Research, Lagos, Nigeria for their support that initiated the choice of this study. The support of Prof. Okaka C.E. of the Department of Animal and Environmental Biology is also highly appreciated.