Five hundred ninety-six (596) specimens of
P. sanguinolentus, ranging in size from 77.3 mm to 165.2 mm carapace width (CW), comprising 294 males and 302 females, were assessed.
Diet composition
Gut contents analysis by points method revealed that crustaceans 31.45% was the top food preference of
P. sanguinolentus (which included appendages, telson, other body parts of prawn, chelipid of crabs, stomatopods), fish(scales, bones, eyeball, vertebrae) formed the secondary preferred food 22.84%, subsequently by mollusc remains (squid tentacles, bivalves, gastropods)18.70% and a large quantities of sand and debris (sand, mud, mesh and plastics)20.29% and miscellaneous items (algae filaments and unidentified matters) 6.68% (Fig 1, 2, 3, 4).
According to the occurrence method, the top food preference was crustaceans, which contributed the most in January (24.76%), followed by November (24.28%) and the least in August (10.71%). Fish remains were recorded maximum in December (19.45%), March followed subsequently (19.393%) and minimum in August (11.6%). Mollusc presence was significantly elevated in quantity during May (22.52%) and less in October (12.65%). Substantial amounts of sand and debris were detected throughout the study period, forming the highest in September (28.04%), followed by August (26.78%) and most down during December (17.64%). Miscellaneous food groups practically occurred in all the stomachs with food particles, with a peak in August (33.03%) and the lowest in May (12.61%) (Fig 5).
Food items in relation to size group
It was observed that juveniles (<80 mm CW) favoured miscellaneous items, with crustacean remains as the next most common component of their diet. In sub-adults (80-100 mm CW), the primary food source categories were crustaceans and miscellaneous. Adults (>100 mm CW) strongly preferred crustaceans and molluscs (Fig 6).
Feeding intensity
Based on the condition of the foregut, crabs were categorized into three groups. Crabs with full and ¾ full were considered active feeders and ½ were considered moderate feeders. Similarly, stomachs with ¼ and empty full were considered to denote poor feeding. Out of 596 stomachs (21.94%) were in full condition, (13.82%) were in 3/4
th full, (19.59%) were in ½ full, (18.13%) were in 1/4
th full and (26.50%) were in empty stomach. The majority of the actively fed crabs (full stomach) were recorded as being highest during December (24.59%), followed by September (22.72%) and least in August (8.46%). Moderately fed crabs were found maximum during October (32.25%), November (22.03%) and minimum in December (11.47%). Poorly fed crabs were recorded highest in August (33.07%), followed by March (30.90%) and lowest during October (16.12%) (Fig 7).
Feeding intensity in relation to size
Actively fed crabs (Highest feeding intensity) were discovered in the size group of 70-80 mm (49.9%) followed by 80-90 mm (26.47%) and least in 160-170 mm (11.53%). Moderately fed crabs were observed maximum in the size group of 100-110 mm (21.25%),140-150 mm (18.18%) and minimum in 150-160 mm. Crabs with empty stomachs were observed across all size groups except the 70-80 mm range, with the majorly occurred in the 130-140 mm (39.68%) and 160-170 mm size group (Fig 8).
Gastro-somatic Index
Gastro-somatic index of
P. sanguinolentus varied from 1.708 to 2.617. The highest value was observed in May (2.617) and minimum in August (1.708) (Fig 9).
Vacuity index
Out of 596 stomachs examined, 159 had empty stomachs (27.10%). The frequency of stomachs being empty was also analysed every month, where August had the most elevated number of empty stomachs (43.07%), followed by November (33.89%), April (32.25%) and May (30.43%) and the most downward was observed in December (14.75%) (Fig 10).
A comprehensive study of aquatic animals’ habits of food and feeding is important to understand their biology, such as growth, reproduction, migration patterns, etc. An organism’s diets vary considerably at different stages of life and the habitat they live in
(Khan et al., 2018). Based on qualitative and quantitative analyses, this research confirmed that
P. sanguinolentus (Fig 11 and 12) is a predator of faunal slow-moving benthic macroinvertebrates like crustaceans and molluscs, miscellaneous items consisting of algal filaments, polychaetes, fish remains and other items such as sand and debris. These findings in this study support those of
Rasheed and Mustaquim, (2018). The most common food items found in their study were crustaceans (small crabs) and fish. Molluscs (gastropods and bivalves) remains were found to be a minor food in this study. Comparable findings have been noted by
Chande and Mgaya (2004) for
P. segnis in Tanzania. The occurrence of fish remains in the gut load of portunids confirms that they exhibit scavenging behaviour that feeds on dead fish (
Prasad and Neelakantan 1988;
Cannicci et al., 1996).
Pooled data revealed the percentage occurrence of feeding habits across various months; crustacean remains formed major food items (20.22%), subsequently by fishre mains (16.93%) and large quantities of sand and debris (23.3%) and mollusc remains (16.5%) and miscellaneous items (22.96%). These observations agree with the study of
Prasad and Neelakantan (1988) on
Scylla serrata from the Karwar region, which showed that portunid crabs mainly fed on crustaceans, detritus, molluscs, fishes and miscellaneous items from Karwar waters (
Prasad and Neelakantan 1988).
Josileen (2011) observed that crustaceans constituted a prominent food group, molluscs constituted the second dominant group and teleost fish were the 3
rd most significant food item for
P. pelagicus from the Mandapam coast in India.
Portunus segnis’s diet mainly depends on local food availability, making it an opportunistic predator.
Hamida (2019) stated that the biological aspects of an organism, such as growth and reproduction, largely depend on the presence of favourite food items or prey organisms.
The blue crab Portunus segnis’s dietary makeup was observed by
Tadi Beni et al., (2019) from Iran, who reported 34.4% of empty stomachs. They concluded that the frequency of empty stomachs varied throughout the study period. In this study, the prevalence of an empty stomach fluctuated across different months, averaging 27.10% overall. The dietary patterns of portunid crabs have been previously studied (
Ropes, 1968;
Patel et al., 1979; Williams, 1982) and they reported that portunid crabs are opportunistic omnivores and rarely feed on motile forms like fish and shrimp species in their diets.
This study noticed fluctuations in dietary patterns concerning different size groups and juveniles strongly preferred miscellaneous and crustaceans. In subadults, crustaceans and other miscellaneous items were the predominant components. Adults showed a clear inclination for crustaceans and molluscs. This conforms to reports of
Sukumaran and Neelakantan (1997) in
P. sanguinolentus.
Khongngain et al. (2017) and
Sarkar et al. (2017) noted that feeding activity varies seasonally due to changes in the availability of preferred food items, maturity stages and spawning seasons. In this investigation also, feeding intensity varied among different months; crabs with full stomachs were observed highest in September (33.33%), 3/4 stomach in December (27.86%), ½ full in October (32.25%), 1/4 full in January (26.75%) and empty stomachs in August (43.07%). Same outcomes have been reported by
Khan et al. (2018), where the feeding intensity was less during the spawning season in
S. serrata.
Whereas in size groups, full stomachs were dominant in the size group of 70-80 mm CW (66.66%) and empty stomachs were highest in the size group 130-140mm CW (39.68%), followed by 160-170 mm CW (38.46%). These observations agree with
Wenner et al. (1974), who noticed that the preying utility is less in adults and relatively more among juveniles.
Freier et al., (1996) state that the impact of larger chela size and muscle mass is probably responsible for the variance in the propensity for food items among crab sizes.
