Introduction

Decapod crustaceans, generally categorized into lobsters, shrimps and crabs are paramount faunal components that are widely distributed in a variety of habitats such as coral reefs, mangroves, estuaries, marine water, freshwater streams, lakes, rivers, seafloor vents, open ocean, ponds, ditches, semi-terrestrial habitats and even in relation with other organisms¹. Diversification among decapods occurred over a period of 455 million years, being recognized by over 3000 fossil species and 15,000 living species distributed among 233 families approximately^2,3. Freshwater crabs complete their entire life cycle in a freshwater ecosystem and do not require marine or brackish ecosystems. They are of great ecological significance and constitute a substantial amount of biomass in the river systems. Within the Brachyura, there is an enormous conglomeration of freshwater crabs and this infra-order is species rich among all the decapods. The diversity of freshwater crabs encompasses approximately 127 species⁴ across the country.

With the increase in human population, the demand for food rich in essential nutrients is rising especially in developing nations. This increasing demand has necessitated the investigation of underutilized natural food resources such as fin and shell fishes. Studies done by Manhas et al. have revealed that shellfishes found in J&K UT are rich sources of proteins and minerals, and thus have tremendous potential in the field of aquaculture⁵. However, only two species of freshwater crabs viz., Maydelliathelphusa masoniana and Himalayapotamon emphysetum are on record from the plain and hilly regions of Jammu and Kashmir Union Territory⁶. The culture of these freshwater crab species will palpably increase the economy of this UT and will act as an important means of subsistence for the fishermen’s community.

The choice of the behavior is closely linked to the ease of hiding place because excavation is effortless where the substrate is made up of small grain sizes⁷. To set up an experiment regarding the habitat choice of any species in the laboratory, it is important to examine its behavior in the natural waters that include their substrate and microhabitat such as coarse sand, gravel, pebbles, fine sand, silt, rocks, leaves, wet grass, moss, and aquatic macrophytes. In the present study, an experiment was conducted to investigate the habitat choice of adult females and males of Himalayapotamon emphysetum under laboratory conditions, using different microhabitats and substrates as the recognition of a suitable substrate is crucial to improve the probability of the survival of any species and to assure the success of recruitment of animal population⁸. Various aspects related to the culture of marine crab species have been addressed in detail by various workers^9,10; however, the insights into freshwater crab culture have been rarely discussed.

Material and Methods

Crab collection was done from the shallow areas of the three different river streams viz., Baba Dhansar, Jhajjar, and Kooh, the tributaries of river Chenab. Crabs were found below the stones, boulders, gravel, and sand. Sometimes, during the heavy flow of water in the streams cast net with 5mmx5mm mesh size was also used for crab collection. The crabs were transported immediately to the laboratory in plastic containers filled with the water of the stream for further experimentation. In the laboratory, acclimatization of the crab specimen was done in dechlorinated water kept in troughs which were prepared by adding sodium thiosulphate to the filtered water. This water was then replaced by filtered water, to which the stream water was also added to maintain the conditions of the natural environment to some extent, to avoid shock due to temperature change and other physical and chemical stress. For constant oxygenation, plastic troughs were equipped with aerators. Different types of substrates and microhabitats were provided to offer shelter to the crab specimen. Live and compound feed was given once a day, especially during early hours, and on every alternate day, the troughs were cleaned properly.

The experiment for the selection of substrate was done first, followed by the experiment for the selection of microhabitat. The experiment was carried out in three different round tubs (62cm in diameter and 31 cm in height), filled with filtered and stream water. All the experiments were carried out at room temperature under natural light conditions. The sides of the rounded tubs were opaque to prevent interference from an external environment. The bottom of Tub-1 was filled with gravel that was 0.3-3 cm in diameter. Similarly, the bottom of tub-2 and tub-3 were filled with stones (20x13x3cm) and cobbles (10-12 cm in diameter) respectively. The substrates were arranged randomly in each container. The first experiment with each substrate was carried out for fifteen consecutive days and the mortality rate of the crabs was recorded.

In the second experiment, the three options selected for the microhabitat were: grass, aquatic plants, and wood fragments. These microhabitats were placed in round plastic containers containing the substrate that was preferred by crabs in the first experiment. About twenty crab specimens were placed in the tubs. Data from the laboratory experiment was analyzed to infer the choice of the substrate and microhabitat preferred by the crab.

Results and Discussion

Continuous monitoring of the experimental setup revealed that out of gravel, stones, and cobbles used in the first experiment, the crab species preferred the substrate consisting of stones. Both male and female individuals prefer to live under the stones. At the time of feeding, they were found to lie at the surface of these stones. In the second experiment, the only substrate used was stones. The same kind of microhabitat was preferred to a significant extent by both the male and female crab species. Both the sexes of crabs selected wood fragments as their microhabitat.

It is essential to consider the substrate and microhabitat among the culture conditions to ameliorate the chances of survival of crab species under laboratory conditions. Crabs attack, kill and eat their species and so the phenomenon of cannibalism is very common among the crabs as reported¹¹. Besides this, aggression and cannibalism reduce the survival rate of Scylla sps¹². However, with the type of substrate and microhabitat preferred by the crab species in the present studies, minimal cannibalism was observed in the trough provided with stones and wood fragments as a large number of crabs were recovered at the end of the experiment.

Experiments conducted in the laboratory revealed that Himalayapotamon emphysetum prefers to live under the stones. This substrate was preferred by all the adult individuals of this crab species (Fig. 1). Mitra and Valarmathi¹³ observed a similar choice of habitat in Himalayapotamon chambaensis, collected from the different localities of Chamba district, Himachal Pradesh. They found that this crab species prefers to live beneath the rocks and boulders in the stream. In a study on the habitat preference of Cryotograspus angulatus, it has been observed that this species preferred muddy, sandy, beaches and even lives under the stones¹⁴. According to their study, the crabs survive better under the stones as they protect the growing individuals. This study is in line with our findings that Himalaypotamon emphysetum live under the stones most of the time and rise to the surface generally at the time of feeding. The literature surveyed revealed that the Hemigraspus sanguineus, Gaetice depressus, Acmaeopleura parvula, Cyclograspus insularum, and C. lavauxi all belonging to the family-Varunidae live under the stones or boulders during low tides^15,16,17. According to them, these crab species use stones as a type of refuge during low tides.

Figure 1: Substrate choice among adult crabs of Himalayapotamon emphysetum. Click here to view figure

The results of Schuwerack et al.,¹⁸ depicted that Macrophthalmus definitus and M. convexus prefer to live under the sea grass and algal mats. Our results for the choice of microhabitat revealed that both males and females of H. emphysetum chose fragments of wood as their microhabitat (Fig. 2). Post-settlement juvenile forms of Menippe mercenaria, are found to inhabit habitats that are complex in structure to avoid predation¹⁹. A similar observation was made in the present study in which the crabs were found beneath the stones in the experimental troughs. The highest mortality among the crab, Paralithodes camtschaticus, kept in the tank provided with sand as a substrate has been observed²⁰. The culture prospects of different crab species in West Bengal have been presented²¹ and it has been reported that the adult individuals of Scylla serrata and Scylla tranquebarica generally remain hidden under the logs of wood. Similar microhabitat i.e., wood fragments were chosen by the species selected for the present study.

Figure 2: Microhabitat choice among adult crabs of Himalayapotamon emphysetum (a) stones and grass (b) stones and aquatic plants (c) stones and wood fragments Click here to view figure

Conclusion

Characterization of the habitat occupied by any crab species provides significant information regarding its successful culture and management. The results of this study revealed that crabs prefer structurally complex substrates for their survival in laboratory conditions as seen in their natural habitat. Knowledge regarding the selection of microhabitat and substrate preference is crucial before taking into consideration the stock enhancement and breeding practice of any crab species. It is expected that the present paper will provide a standard protocol to the researchers for carrying out the future research on the culture of Himalayapotamon emphysetum which can be further helpful to the farming community.

Acknowledgement

The authors would like to thank Department of Science and Technology (DST), Government of India (GOI) for providing necessary facilities under Fund for improvement of S&T infrastructure (FIST) and Promotion of university research and excellence (PURSE) programs. The valuable suggestions and help provided by Head, Department of Zoology, University of Jammu is duly acknowledged.

Conflict of Interest

The authors declare no conflict of interest.

Funding Sources

There is no funding sources.

References

1. Wolfe J.M., Breinholt J.W., Crandall K.A., Lemmon A.R., Lemmon E.M., Timm L.E., Siddall M.E., Bracken-Grissom H.D. A phylogenomic framework, evolutionary timeline and genomic resources for comparative studies of decapod crustaceans. Proceedings of the Royal Society B: Biological Sciences. 2019;286:20190079.
   CrossRef
2. De Grave S., Pentcheff N.D., Ahyong S.T., Chan T.Y., Crandall K.A., Dworschak P.C., Felder D.L., Feldmann R.M., Fransen C.H.J.M., Goulding L.Y.D., Lemaitre R., Low M.E.Y., Martin J.W., Ng P.K.L., Schweitzer C.E., Tan S.H., Tshudy D., Wetzer R. A Classification of Living and Fossil Genera of Decapod Crustaceans.Raffles Bulletin of Zoology. 2009;Supplement:1–109.
3. Bracken H.D., De Grave S., Toon A., Felder D.L., Crandall K.A. Phylogenetic position, systematic status, and divergence time of the Procarididea (Crustacea: Decapoda). Zoologica Scripta.2010;39:198–212.
   CrossRef
4. PatiK. Two new species of freshwater crabs of the genusPotamiscus Alcock, 1909 (Brachyura: Potamidae) from Nagaland, northeastern India. Nauplius – The Journal of the Brazilian Crustacean Society. 2021;29: e2021006. 
   CrossRef
5. Manhas P. Studies on some nutritional aspects and clinical significance of shell fishes prawns and crabs of Jammu region of J and K state. Ph.D thesis. University of Jammu, Zoology Department. 2017.
6. Bandral M., Gupta K., Langer S. Inventory on the diversity of fresh water crabs in some water bodies of Jammu (J&K) North India. Journal of International Academic Research for Multidisciplinary. 2014;2(9): 330-341.
7. Dall W., Hill B.J., Rothlisberg P.C., Staples D.J. The Biology of the Penaeidae. Advances in Marine Biology, Academic Press, London. 1990;pp489.
8. Zenone A., Badalamenti F., Giacalone V.M., Musco L., Pipitone C., Fernández T.V., Anna G.D. Substrate preference and settlement behaviour of the megalopa of the invasive crab Percnon gibbesi (Decapoda, Percnidae) in the Mediterranean Sea. Helgoland Marine Research 2016;70:21.
   CrossRef
9. Galley T.H., Green B.C., Watkins L., Vay L.L. Development of larval culture techniques for the shore crab, Carcinus maenas (L) Aquacult Int 2011; 19:381–394.
   CrossRef
10. Syafaat M.N., Azra M.N., Waiho K., Fazhan H., Abol-Munafi A.B., Ishak S.D., Syahnon M., Ghazali A., Ma H., Ikhwanuddin M. A Review of the Nursery Culture of Mud Crabs, Genus Scylla: Current Progress and Future Directions. Animals (Basel). 2021;11(7):2034.
    CrossRef
11. Roy P., Chandan C.S.S., Roy N.C, Islam I. Feed types affect the growth survival and cannibalism in early juvenile of striped snakehead (Channa striata ). Egyptian Journal of Aquatic Research. 2020;46 377–382.
    CrossRef
12. Sanda T., Shimizu T., Dan S., Hamasaki K. Effect of body size on cannibalism in juvenile mud crab Scylla serrata (Decapoda: Brachyura: Portunidae) under laboratory conditions. Crustacean Research. 2021;50: 87–93.
    CrossRef
13. Mitra S., Valarmathi K. Himalayapotamon chambaensis, a new species of freshwater crab (Crustacea: Brachyura: Potamidae) from Himachal Pradesh, India. Zootaxa. 2017;4324(3):482–490.
    CrossRef
14. Spivak E., Anger K, Luppi T, Bas C, Ismael D. Distribution and habitat preferences of two grapsid crab species in Mar Chiquita Lagoon (Province of Buenos Aires, Argentina). Helgoländer Meeresuntersuchungen. 1994;48:59-78.
    CrossRef
15. Lohrer A., Fukui Y., Wada K., Whitlatch R (2000) Structural complexity and vertical zonation of intertidal crabs, with focus on habitat requirements of the invasive Asian shore crab, Hemigrapsus sanguineus (de Haan). Journal of Experimental Marine Biology and Ecology.2000;244:203–217.
    CrossRef
16. Brousseau D., Baglivo J., Filipowicz A., Sego L., Alt C. An experimental Weld study of site Wdelity and mobility in the Asian shore crab, Hemigrapusus sanguineus. Northeastern Nat. 2002;9:381–390.
    CrossRef
17. Brockerhoff A., McLay C. Comparative analysis of the mating strategies in grapsid crabs with special references to the intertidal crabs Cyclograpsus lavauxi and Helice crassa (Decapoda: Grapsidae) from New Zealand. Journal of Crustacean Biology. 2005;25:507–520.
    CrossRef
18. Schuwerack P.M.P., Barnes R.S.K., Underwood G.J.C., Jones P.W. (2006) Gender and Species Differences in Sentinel Crabs (Macrophthalmus) Feeding on an Indonesian Mudflat. Journal of Crustacean Biology. 26(2):119-123.
    CrossRef
19. Krimsky, L.S., Epifanio, C.E. Multiple cues from multiple habitats: effect on metamorphosis of the Florida stone crab, Menippe mercenaria. Journal of Experimental Marine Biology and Ecology. 2008;358:178–184.
    CrossRef
20. Stevens B. Settlement, substratum preference, and survival of red king crab Paralithodes camtschaticus (Tilesius, 1815) glaucothoe on natural substrata in the laboratory. Journal of Experimental Marine Biology and Ecology. 2003;283:63 –78.
    CrossRef
21. Roy M.K.D, Nandi N.C. Culturable crabs of coastal West Bengal: an overview. Journal of Aquaculture & Marine Biology. 2019;8(1): 1-5 .
    CrossRef