Attempted Predation and Prey Handling of Fish by the Checkered Keelback, Fowlea Piscator (Schneider, 1799) in Nepal (Serpentes: Natricidae)
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Herpetology Notes, volume 13: 1073-1077 (2020) (published online on 28 December 2020) You can’t always get what you want: attempted predation and prey handling of fish by the Checkered Keelback, Fowlea piscator (Schneider, 1799) in Nepal (Serpentes: Natricidae) Kamal Devkota1,*, Ayush Maharjan2, and Hinrich Kaiser3 The Checkered Keelback, Fowlea piscator (Schneider, During photography walks, the second author (AM) 1799)4 has an extensive distribution in South Asia, made serendipitous observations of encountered including Nepal, and throughout Southeast Asia herpetofauna at Taudaha Lake (27.6481°N, 85.2816°E, (Schleich and Kästle, 2002; Shah and Tiwari, 2004; elevation 1287 m), a small (4.63 km2) lake on the Whitaker and Captain, 2004; Das, 2010, 2012). It is a outskirts of Nepal’s capital city, Kathmandu. The fairly common aquatic snake that inhabits areas around lake and the surrounding area have experienced some freshwater bodies, rice fields, and marshy areas of human impact, but they are less polluted than the more lowlands and hills, entering the water while foraging urban water bodies and there is a significant diversity for a variety of prey during both day and night (Ahsan, of resident and migratory birds (Shrestha and Adhikari, 1983; Hossain, 2016; Parmar, 2018). Young snakes feed 2016). Among the fish, the population of native on aquatic insects, frog eggs, and tadpoles, whereas barbs, catfishes, and snakeheads is being disrupted adults prey on fish, frogs, and occasionally on rodents by several introduced carps, including Bighead Carp and birds (Shah and Tiwari, 2004; Whitaker and Captain, (Hypophthalmichthys nobilis), Common Carp (Cyprinus 2004). Almost the entire literature on feeding in this carpio), Grass Carp (Ctenopharyngodon idella), and species consists of reports from India, but websites in Silver Carp (H. molitrix). Our observations detail two other countries (e.g., Taiwan: Breuer and Murphy, 2010; predation attempts by F. piscator on fish, one on a native Thailand: Thai National Parks, 2020) and reports about catfish and the other on an introduced carp. parasitic infections (e.g., Indonesia: Audini et al., 2017) indicate that prey organisms listed for India are likely Results and Discussion taken by F. piscator throughout its range. Even though Observation 1.—At 13:50 h on 29 May 2019, AM this snake is a prominent member of the herpetofauna of walked near Taudaha Lake and encountered an adult Nepal, there have not been many reports on its feeding F. piscator pursuing a catfish (likely Clarias magur5) ecology in that country. Here we report two predation swimming near the water surface. He spotted the attempts by Fowlea piscator on two types of fish, catfish and carp, at Taudaha, Kathmandu, Nepal, which ultimately failed but provide an example for differential prey handling by this snake. 4 Most of the reports in the literature on the feeding of this species give its name as Xenochrophis piscator. However, the species piscator was recently reassigned to the genus Fowlea by Pur- kayastha et al. (2018) and we follow their recommendations. 1 Nepal Toxinology Association, Major Chowk, Kawasoti-8, 5 We asked several colleagues to assist with the identification of Nawalpur, Nepal. the catfish, but our images do not reveal complete views of the 2 Himalayan College of Agricultural Sciences and Technology, fish, making this a difficult task. Based on the faintly visible Kathmandu, Nepal. lateral line system we believe the catfish is not a member of 3 Department of Vertebrate Zoology, Zoologisches the genus Glyptothorax but of the genus Clarias. Of the two Forschungsmuseum Alexander Koenig, Adenauerallee species to most likely be encountered in Taudaha Lake, the 160, 53113 Bonn, Germany; and Department of Biology, darker belly colouration would indicate that the fish can be Victor Valley College, 18422 Bear Valley Road, Victorville, identified as C. magur. Whereas accurate prey species identity California 92395, USA. is not significant to our report or in a generalist predator, we * Corresponding author. E-mail: [email protected] attempted identifying the prey to the best of our ability. 1074 Kamal Devkota et al. approximately 1-m-long snake swimming actively (2017) and Kalki (2020), who documented F. piscator towards its desired prey, and it was able to strike at it feeding on the eggs of Rhacophorus malabaricus inside in the water and hold onto it with its teeth (Fig. 1A). the foam nest of these treefrogs, and Moktadir and Hasan The fish was relatively large in comparison with the (2016), who reported that F. piscator consumed boiled snake’s head, and it struggled violently to free itself rice and cooked chicken from a student dormitory’s from the snake. The fish struggled for ca. 15 min and cafeteria outlet drain at night on two consecutive days finally succumbed to its injuries. After the fish ceased on the campus of Jahangirnagar University in Dhaka, struggling, the snake tried to swallow it while remaining Bangladesh. It would certainly appear that either fish in the water. However, perhaps due to size of the fish and the difficulty with manoeuvring slippery prey into an ideal position for ingestion, the snake was unable to consume the fish. After a few minutes of trying to eat the fish, the snake pulled the fish into a nook in the rock wall near the bank of the lake (Fig. 1B). It struggled there once again to swallow the fish (Fig. 1C) but was ultimately unable to do so. After several attempts and struggles, the snake departed and left the dead fish behind. The various scrapes and cuts on the body of the catfish and the changing position of the snake’s head during our observations (Fig. 1B, C) attest to the struggles of trying to subdue the fish and then to swallow it. The observation lasted ca. 35 min. Observation 2.—During another walk at Taudaha Lake, AM again encountered an adult F. piscator, at 12:45 h on 29 November 2019, this time chasing a Common Carp (Cyprinus carpio). He witnessed the capture and followed the snake swimming in the water with the fish in its mouth (Fig. 2A). This fish was also large in size and struggling to free itself from the snake’s grasp, but it eventually ceased struggling and died (Fig. 2B). Unlike in the observation with the catfish, this snake did not attempt to swallow the carp while remaining in the water. Instead, it kept a firm bite in the same position for the entire time of the observation and moved the fish to the lakeside rocks (Fig. 2C). It remained among the rocks for a few minutes with the carp held up out of the water (Fig. 2D). It subsequently attempted to swallow the fish but was unable to do so. Eventually, the keelback disengaged and left the fish among the rocks. The total time taken for these activities was about 20 min. Figure 1. Feeding attempt on 29 May 2019 by an adult Studies on the diet of F. piscator from across its range Fowlea piscator to capture and consume a catfish (likely include Norval et al. (2010), who reported predation Clarias magur) in Taudaha Lake near Kathmandu, Nepal. (A) on a microhylid frog (Microhyla heymonsi) and a fish Having bitten, subdued, and killed the fish, the snake engaged in several futile attempts to ingest it while remaining in the (the snakehead Channa asiatica) in Taiwan, Whitaker open water. (B) Having failed to swallow the catfish in the and Captain (2004), who reported its diet from Indian open water, the snake landed it and tried again at the water’s populations, and Hossain (2016), who recorded that edge. (C) Finally, after dragging its desired prey into the the major food items of F. piscator in Bangladesh were rocks bordering the lake, the snake again tried in vain several insects (56.5%), fish (26.1%), and amphibians (17.4%). times to consume the dead fish. Multiple injuries to the fish Among the more unusual observations on predation in sustained while handled by the snake are visible. Photos by F. piscator are observations by Phansalkar and Gowande Ayush Maharjan. Attempted predation and prey handling of fish by the Checkered Keelback 1075 species in our observations would fall well within the (Nilssonia hurum) in Jagadishpur Reservoir, Kapilvastu, expected food spectrum of F. piscator. Nepal, an attempt that was likely also unsuccessful Clearly, each of the snakes we observed made an based on the width of the turtle’s carapace relative to the error in determining how to optimally exert its energy size of the snake’s head (the observation was fleeting to capture food, given that neither was successful in and when the snake disappeared from view it had not its attempt to eat the large fish. According to Greene yet swallowed the turtle; Kritagaya Gyawali, in litt.). (1997), colubrids commonly prey on animals weighing Another instance of poor judgment by a checkered about 20% of their own mass, with gape width generally keelback was reported by Patel et al. (2017), who found a determining factor. Prior to our observations, Gyawali a dead keelback that appeared to have been killed by the (2019) reported an episode of F. piscator attempting spines of its intended fish prey. to feed on a juvenile Indian Peacock softshell turtle Explanations for such odd occurrences may lie with Figure 2. Feeding attempt on 29 November 2019 by an adult Fowlea piscator to capture and consume a carp (Cyprinus carpio) in Taudaha Lake near Kathmandu, Nepal. (A) After getting a firm grip on the fish, the snake swam while holding on to the fish until it died. (B) The snake elevated its head above the water level to move the fish, retaining a firm bite at an area dorsal to the anal fin.