Dietary Overlap between Native and Exotic Fishes revealed through Gut Content Analysis at Head Baloki, Punjab, Pakistan

An imminent threat to indigenous freshwater ichthyofauna is the introduction of alien fishes that can alter the behavior, population dynamics and native community structure. Thus, it is necessary to understand their feeding behaviour to avoid any unwanted incalculable loss. At sampling site, Head Baloki feeding habits both of native (L. calbasu, C. catla, L. rohita and C. mrigala) and alien (H. nobilis, H. molitrix, C. carpio, C. idella, C. auratus, O. aureus, O. niloticus and O. mozambicus) species were analyzed through frequency of occurrence and percentage by number from January 2017-December 2019. Results indicated that L. rohita remained herbivorous while L. calbasu, C. catla, C. idella and both C. carpio and C. mrigala were detritivore, planktivore, phytoplanktivore and generalist feeders, respectively. H. molitrix and C. auratus showed planktivorus and generalist feeding behaviour, respectively. Tilapia species enlisted as detritivores Whereas, H. nobilis was generalist feeder. Complex dietary overlap has been observed between different co-existing species. Current study has uncovered some surprising results where diet of O. niloticus was altered as detritus feeder. Change in feeding habit of alien fishes is the strategy to make them successful that is in line with current findings from freshwater ecosystem of Punjab, Pakistan.


INTRODUCTION
The alien species may cause a drastic impact on already stable native fish faun of freshwater ecosystems however succession predictor characteristics of species which promote invasion success are few in number and are different from one system to the other (Ribeiro et al., 2008). It is therefore suggested that investigation of system and species is required to answer the question in particular way (Van-Kleunen et al., 2010). The trophic cascade of alien species in invaded habitats can predict and evaluate their success in new habitats. According to Marchetti et al., (2004), ecological generalist with strong physiological tolerance can be the powerfully established aliens in any new population.

Biological
invasion induces economic and ecological consequences worldwide (Gozlan et al., 2010). Fishes are introduced more because it has a strong interaction with human being. Some alien fish species cannot establish in selfsustained ecosystem while few established communities are not impacted by aliens (Gozlan, 2008). A strong literature body indicates that invader species have a strong effect on native populations which range from gene to an ecosystem level (Cambray, 2003;Cucherousset & Olden, 2011) but various impacts still have not been culminated. A fish in a new ecosystem may be added due mainly to four basic reasons including angling/sport, aquaculture, fisheries and ornamental purposes (Gozlan, 2008).
Alien fishes are generally lager than the native ones which is a biological trait leading to the invasive success (Miller et al., 2002;Blanchet et al., 2010). Trophic position of an organism in an ecosystem is also determined by the size of animal's body (Hildrew et al., 2007). Introduction of a large body alien animal in an ecosystem can develop an interaction with prey, predator and competitor. The new competition between alien and native fish may develop indirectly (trophic cascade) or directly (predation and competition) which may affect the native food web and community dynamics (Lockwood et al., 2007). It is required to investigate the ecological impact induced by alien fish on aquatic ecosystem that already has disturbed by the challenging human activities (Cucherousset & Olden, 2011).
Competition between two co existing species for resource acts as a limiting factor for shaping the community as in the case of geography and climate which are abiotic factors of the environment. Interspecific competition impacts both the species, negatively. Resources get exploited by the alien population (Molles, 2002). Each population has a dietary and fundamental niche. Members of the population mostly use possible diet as a subset which depends upon the dietary niche of the concerned population (Stephens et al., 2007). Both intraspecific and interspecific competition helps to find out the resources which belong to respective dietary niche (Stephens et al., 2007;Araujo et al., 2011).
In new habitats the trophic dynamics are important to predict the potential impact of invader species. Kolar and Lodge, (2002) demonstrated that alien species having broad dietary niche are more successful in establishing the new population.
Reservoirs face various anthropogenic disturbances than natural water bodies especially lakes which are ranging from public assessment to the water level fluctuations and face higher variability in its nature (Leira and Cantonati, 2008). It is also found that reservoirs are less resistant to the alien species and lakes are more susceptible to invasiveness (Johnson et al., 2008).
Exotic fishes such as O. niloticus, O. mozambicus, C. idella, H. nobilis and C. carpio were imported in 1985(De Silva, 2004), 1954(Naik 1973), 1964(FAO, 1970), 1975(Mahboob and Sheri, 1997) and 1964(FISHBASE, 2003 (FAO, 1970) and C. auratus (Mirza, 2003) were imported with unknown source. The alien fishes were introduced to promote Aquaculture practices, to control aquatic weeds, to promote ornamental culture and enhancement of sport fishing in Pakistan (khan et al. 2011). Alien fishes Compete with native fishes because they breed in shallow water, mother is mouth breeder, modify food and stabilize in changing food resources De Silva, (2004). Current study is designed to report actual mission of alien fishes in disturbed aquatic ecosystem of Pakistan. Invisibility of alien fishes is almost higher in disturbed ecosystem (Davis et al. 2017) that is driven by two basic phenomenon such as vacant and empty niches (Turetsky et al., 2017;Fridley and Sax, 2014;Lekevičius, 2009).

MATERIALS AND METHODS
The sampling was conducted from the year 2017 to 2019 in the territory of Punjab Province, Pakistan from Head Baloki, River Ravi (31°23'23 N; 73°86'90 E) (Figure 1).
The sampling was made twice in the month of January, April, August and December throughout the whole study period to collect maximum number of samples. Data based on Global Positioning System (GPS) was collected from selected sampling site and recorded in Table 1. Targeted fish species were captured through cast nets, drag nets and hand nets. Gill nets with same length of (10 m) and height of (1.6 m), but with meshes varying from 15 to 110 millimeter, knot-knot (Khan et al., 2011) Appropriate identification keys were used to identify the samples up to the species level (Mirza and Sharif, 1996;Talwar and Jhingran, 1991). Values of Schoener index ranges from 0 (overlap is absent) to 1(complete overlap between two species). 0.6 values indicated a significant overlap of diet item between two species (Schoener, 1974).

S. No
Fish Species *S.T **I.S ***T.S.S Phytoplanktons, macrophytes and zooplanktons were present in 100% and unidentified matter in 50% whereas higher invertebrates, fish/fish parts, mud/sand and detritus were the least preferred food as reported in 0% of the examined guts of L. rohita.
Its food comprised of phytoplanktons, macrophytes, zooplanktons and unidentified matter as 50.50%, 45.50%, 3.50% and 0.50%, respectively whereas other food categories (H, F, MS and D) remained absent in the examined gut of L. rohita. IRI & %IRI indicated that Phytoplankton>Macrophytes>zooplankton >undifferentiated matter>higher invertebrates, fish/fish parts, mud/sand and detritus was the food selection pattern of L. rohita. L.rohita did not show any significant dietary competition with other reported fish species (Table 2).
The occurrence frequency of phytoplanktons, macrophytes, zooplanktons, unidentified matter, mud/sand and detritus was 100% in L. calbasu while higher invertebrates and fish/fish parts remained absent in same fish. Major food of L. calbasu was based on detritus which comprised about 91.80% (undifferentiated matter, mud/sand and detritus as 0.50, 1.50 and 89.80%, respectively). Plant based diet was 5.70% (phytoplankton 4.40 and macrophytes 1.30%) of the total consumed food. The least consumed food 2.50% by L. calbasu was animal based (zooplankton as 2.50% while higher invertebrates and fish/fish parts remained 0%). According to %IRI L. calbasu preferred food as Detritus>Phytoplanktons>zooplanktons>m ud/sand>macrophytes> undifferentiated matter. Higher invertebrates and fish/fish parts were not found from any one of the examined gut (Table 3). L. calbasu showed a significant dietary competition with three tilapia species (O. niloticus, O. aureus and O. mozambicus) ( Table 2).
Phytoplanktons, macrophytes, zooplanktons, unidentified matter, mud/sand and detritus were found in all (100%) examined guts of C. catla whereas occurrence frequency of higher invertebrates and fish/fish part remained 0%.
According to percentage analysis plants (phytoplanktons 40.00% and macrophytes 4.00%) and animals based (zooplanktons 53.00%, higher invertebrates and fish/fish parts as 0.00%) whereas detritus based diet comprised only 3.00% (undifferentiated matter, mud/sand and detritus as 2.00%, 0.50% and 0.50% respectively) of total consumed food. zooplankton>phytoplankton>macrophytes >undifferentiated matter>mud/sand and detritus was the food preference strategy of C. catla in wild habitat at Head Baloki. Higher invertebrates and fish/fish parts were not observed form the analyzed fish guts (Table 3). C. catla diet significantly overlapped with an alien fish H. molitrix (Table 2).
Current study demonstrated that phytoplankton, macrophytes, zooplankton, higher invertebrates, fish/fish parts, mud/sand and detritus were observes in all (100%) processed guts of C. mrigala. Results indicated that it takes detritus based diet that is about 49.50% (detritus, mud/sand and undifferentiated matter as 39.50%, 5.50% and 4.50% respectively) while plant based diet was 26.80% of the consumed diet (Phytoplanktons 21.50% and macrophytes 5.30%). animals based diet was consumed about 23.70% (zooplanktons, higher invertebrates and fish/fish parts as 19.20%, 4.30% and 0.20% respectively). Detritus>phytoplankton>zooplankton>mu d/sand>macrophytes>undifferentiated matter>higher invertebrates>fish/fish parts is the food preference strategy of the C. mrigala as mentioned in table 2.    (Table 2). C. idella did not show significant diet overlap with any other selected specie at Head Baloki (Table 3).
Phytoplanktons, macrophytes, zooplanktons unidentified matter, mud/sand and detritus food contents showed the 100 whereas higher invertebrates and fish/fish parts as 50 and 0% frequency of occurrence in processed guts of O. niloticus. Present study investigated that O. niloticus's major portion of diet is based on detritus 92.00% (detritus, mud/sand and unidentified matter as 90.00, 1.50 and 0.50% respectively) followed by plant matter 5.00 % (4.00% phytoplanktons and 1.00% of macrophytes) and animal based 2.50% (zooplanktons, higher invertebrates and fish/fish parts and as 2.00%, 0.50% and 0.00% respectively) consisted of diet based on animals.  (Table 3).
O. mozambicus significantly overlapped its diet with three species including two aliens (O. niloticus and O. aureus) and one native (L. calbasu) of the Punjab, Pakistan (Table  3).

DISCUSSION
Mahboob, (2011) investigated the major food component of L. rohita is composed of Phytoplanktons (70-80%) followed by zooplanktons (25-30%) which supports current investigations as L. rohita comparatively have large openings in filtering apparatus thus it takes large sized food particles (Khaing and Khaing, 2020). Imran et al. (2014) corroborated the current investigation by nominating the L. calbasu as bottom dwelling fish that mainly feeds on detritus whereas macrophytes, zooplanktons and Phytoplanktons were also found from processed guts. Khabade, (2015) investigated that C. catla is an omnivore surface feeder whose adult members feed on algae, higher invertebrates and vegetable debris. Mahboob, (2011) is in line with the current study reporting that the C. mrigala is a generalist feeder. Soni and Ujjania, (2018) reported that major food C. mrigala consists of detritus while small portion was unicellular algae, filamentous algae and plant matter endorsing the current picture. H. molitrix took plankton based diet while H. nobilis was found to be a general feeder. Cremer and Smitherman, (1980) reported that both silver and bighead carps (Asian carps) mainly feed on zoo and Phytoplanktons based on the structure of their gill rakers (Bighead carp 20-60 µm and silver carp 20-25 µm) and compete with native filter feeding fishes.
C. idella is phytoplanktivore specie that preferably eed on plant matter. Milstein and Svirsky (1996) narrated that major food component of C. idella is plant based matter while zooplanktons remained in the recessive food category probably due to feeding habit. It was further explained that C. idella intake variable food based on its availability (available prey organism), interaction and combination of species. Khan et al. (2016) reported supporting results that C. carpio feeds primarily on decaying floral matter and benthic fauna at the bottom of water body. Due to high tolerance against temperature and turbidity C. carpio have more growth rate than native C. mrigala also feeding at bottom (Parameswaran et al., 1971). Current study indicates that C. auratus is a generalist feeder. Saoud, (2006)  Fishes have wide range of feeding habits ranging from herbivore-detritus feeder based on resource availability which is reflection of fish behavior (morphology and physiology) along with the consumed food. Alien fishes (surprising concern O. niloticus) have wide range of feeding habits than indigenous fish fauna that tells the story of their successful survival in fatly changing aquatic ecosystem of Punjab, Pakistan. Dietary overlap between alien and native fishes is due to high fecundity, feeding on general food categories and tolerance (temperature and turbidity) of alien fishes to survive in invasive environment.

CONCLUSION
The human activities like urbanization, species introduction, change in climate, destruction of habitat and pollution are causing the jeoparadism of fish community worldwide (Abilhoa et al., 2011). Study of feeding ecology is necessary because there is a strong link between population dynamics and understanding the subject such as prey selection strategy (Motta and Wilga, 2001). Alien fishes have wide range of feeding habits ranging from herbivoredetritus feeder based on resource availability than indigenous fish fauna that tells the story of their successful survival in fastly changing aquatic ecosystem of Punjab, Pakistan. Diet overlap between indigenous and alien fish fauna has ecological perspectives and needs different aspects to produce a clear picture. Dietary overlap between alien and native fishes may be due to high fecundity, feeding on general food categories and tolerance (temperature and turbidity) of alien fishes. Further, it is recommended that by using analysis of Stable Isotope and Gut Content from large number of fish samples can provide a vibrant picture on feeding competition among native and alien fishes.