J. Indian Fish. Assoc., 33: 31-47, 2006 31
NATURAL DIET OF PENAIED PRAWNS IN THE COASTAL WATERS OF MUMBAI
V. D. Deshmukh, M. S. Sawant, S. J. Mane and A. S. Hule Mumbai Research Centre of Centrallvfarine Fisheries Research Institute, Army & Navy Building, 2nd Flo01~ M.G. Road, Mumbai- 400 001, India
ABSTRACT
Foregut contents of eight commercially important species of penaeid prawns namely Penaeus merguiensis, Metapenaeus affinis, M. monoceros, M. brevicornis, Parapenaeopsis stylifera, P. lwrdwickii, P. ,r,'culptilis and Solenocera crassicornis were investigated from inshore, nearshore and offshore fishing grounds ofMumbai. Feeding intensity and index of preponderance (IP) of the dietary items were compared statistically for the species, sexes, fishing areas and maturity condition of females. AU the species except M. monoceros and P. sculptilis showed that females were better fed than males. The feeding intensity in the three depth-zones was different for M. affinis, M. brevicornis, M. monoceros, P. hardwickii and S. crassicornis, and un.iform for P. merguiensis, P. stylifera and P. sculptilis. Acetes spp., prawn remains, polychaetes, benthic crustaceans, foraminifers and fish remains were the important food items of the prawns. Dietary comparison between the two sexes of the species did not show any difference, but mature females of M. monoceros and P. sculptilis had different diets. Comparison of food items for all the species together showed significant difference between the three areas. Crustacean diet was the favourite in the inshore and nearshore, and polychaetes in the offshore waters. All the species except P. hardwickii showed difference in their dietary composition in the three depth-zones. It is concluded that these coexisting species are primarily carnivorous and exhibit diverse food preferences in different depth-zones by browsing on interstitial organisms, chasing epipelagic prey, raptorial predation, scavenging on dead organisms or adopting different temporal abundance to avoid inter-specific competition for food.
Keywords: Foregut, penaeid prawns, diet inter-specificity
INTRODUCTION migration to offshore waters for spawning. Mangrove-fringed estuaries Life cycle of the coastal penaeid are the food-rich nursery grounds which prawns is characterised by nursery provide detritus and benthic organisms grounds in estuarine waters and to their young ones for rapid growth 32 Y. D. Dcshmukh. M.S. Sawant, S. J. Mane and A. S. Hulc
(Garcia and Le Reste, 1981 ). However, Wassenberg and Hill ( 1987), Stoner and young ones of most of the species, Zimmerman ( 1988), andAlbertoni et al. which do not exhibit such obligatory (2003). dependency on the estuarine waters, abound in coastal mudflats and areas Penaeid prawns belonging to the close to the shores (Hughes, 1966; genera Metapenaeus, Parapeneopsis Kutkunh, 1969~ Staples et al., 1985), and Solenocera form bulk of the primarily for feeding. Before migrating traditional bag (dol) net and trawl to offshore waters, juveniles and sub catches in waters around Mumbai adults of these prawns traverse through (Deshmukh et al., 2001 ). Juveniles and inshore and nearshore habitats, where sub-adults of these genera occur benthic communities on the inte1iidal abundantly in the inshore creeks and and subtidal mudflats offer rich feeding nearshore waters from where they grounds to them. During their sojourn migrate to offshore waters for through such habitats, the species may spawning. The abundance ofprawns in show temporal and spatial feeding these waters could be due to profusion intensity or preference to certain food of food; therefore, it was intended to organisms to avoid competition among know the food and feeding habits of the them. Therefore, it is necessary to prawns in the inshore, nearshore and understand the interaction between offshore habitats. Since many coexisting species in relation to the coexisting species of prawns share the distribution of food organisms, which same habitats, it is imperative to explore can throw light on the habitat value species-wise and area-wise feeding (Minello and Zim1nennan, 1991 ). niches, and their individual preferences to particular food organisms. An Investigations on the food and attempt was also made to find out feeding habits of the individual species preference of either sex, in general, and in India have been reported with respect the mature females, in pmiicular, to to size and season (Panikkar and ce1iain food organisms. Menon, 1956; Kunju, 1967; George, 1974). The intensities of feeding and MATERIAL AND METHODS diet of prawns in different areas have been reported for Penaeus semisulcatus Random samples of eight species, (Thomas, 1980), P merguiensis (Chong viz., Penaeus merguiensis, and Sasekumar, 1981) and M. Metapenaeus G:ffinis, M. 1nonoceros, M. monoceros (Rao, 1988). Comparative brevicornis, Parapeneopsis styl~fera, P accounts of food of two or more species sculptilis, P hardwickii and Solenocera in different coastal areas have been crassicornis were collected during given by Dall (1968), Tiews et al. January-December 2002, frmn New (1968) and Kuttyamma. (1974). Ferry Wharf (NFW), Versova and Quantitative comparisons of the food Sassoon Docks landing centres at between the species are reported by fortnightly intervals from trawl and dol NATURAL DIET OF PENAJED PRAWNS IN THE COASTAL 33 WATERS OF MUMBAI nets. The samples collected from dol Elphidium spp. and Cyclammina spp. as nets operated in Mumbai Harbour and foraminifers. Generally, small fishes or landed at NFW and Sassoon Docks their larvae ingested by the prawns were represented inshore area (depth: < 10 m) identified by the presence of scales, and those from trawlers operated from bones, vertebrae and eye lenses. Entire Versova represented nearshore area shells · or pieces with ridges and (depth: 10-25 m), while those from the adductor muscles were the keys to multi-day trawlers at NFW represented identify bivalves, and spiral shells (and the offshore area (depth: 25-70 m). sometimes opercula) marked the Samples. of M monoceros and P presence of gastropods, while pieces of sculptilis were not available from arms with suckers enabled to nearshore and offshore areas, distinguish cephalopods. Small pieces respectively. The samples were of leaves, filaments of algae and preserved in 5% formalin. After noting siliceous diatoms were together size and sex, and maturity conditions in grouped as vegetable matter. Partly the case of females, the carapace of each digested semi-solid food that could not was cut open to observe distension of be identified to its origin was treated as foregut. The foreguts were dissected to semi-digested matter (SDM). find out feeding intensity and their Entangled thread-like material contents. appearing like nylon threads and white beads could not be identified The gut contents were examined (unidentified). The decomposed under stereoscopic binocular amorphous plant and animal matter, and microscope and categorized into broad their remains mixed with mud were taxonomic groups. Acetes spp. were treated as detritus. identified by the presence of elongated eyestalks and uropods with red Feeding intensity of 6425 chrmnatophores. Pieces of penaeid and specimens of the eight species was caridean prawns (prawn remains) in the determined by assigning 0-20 poinfs fore guts were identified by the presence depending on distension of foreguts. of antennal flagella, eyes, white mass of The prawns with 12-20 points were flesh and appendages. The polychaetes considered as well-fed, 5-11 points appeared as entangled mass with partly-fed and 0-4 points poorly-fed. distinct setae, jaws and sometimes, The intensities of feeding between the eletrae. Benthic crustaceans included sexes and maturity conditions of isopods, amphipods, harpacticoid I females were compared statistically by copepods, ostracods, cumaceans, the test of homogeneity while the same tanaedaceans and small crabs, which in inshore, nearshore and offshore areas were identified by the presence of their by the test of independence by 2 peculiar body parts and appendages. computing the X • Based on the visual The presence of typical chambered estimates of their volume, the recorded shells made it easy to identify food items were given points, and the 34 V. D. Dcshmukh. M. S. Sa want. S. J. Mane and A. S. Hulc percentage volume and percentage females were noted following Rao occurrence were calculated to get the (1968); the differences in the diet of index of preponderance (IP) as mature (stages III and IV) and non suggested by Natarajan and Jhingran mature females (stages I, II and V) were (1961). For the comparison of dietary also tested statistically by the items between the sexes and the areas, Spearman's rank correlation method. the IP of the food items were analysed using non-parametric Spearman rank RESULTS correlation method (Zar, 1984 ). The difference in preference of food items Feeding intensity: Sex-wise feeding between the species was found by the intensity of each species pooled from non-parametric Friedman's test (Zar, the inshore, nearshore and offshore 1984). The maturity conditions of areas (Table 1) showed that the proportion of moderately and well-fed Table 1: Feeding intensity of male and female prawns C'/o in. parentheses) pooled from all the areas
Species Sex Pool'ly fed !VIoderately fed Well Fed Results x2 P. merguiensis Male 97 (63.0) 36 (23.4) 21 (13.6) female 82 (50.0) 40 (24.4) 42 (25.6) 8.16* Pooled 1 79 (56.3) 76 (23.9) 63 (19.8) M. C{j{in is Male 388 (57.9) 135 (20.1) 147(21.9) Female 428 (52.1) 181 (22.0 212(25.8) 5.19* Pooled 816(54.7) 316(21.2) 359 (24.1) M. monoceros Male 96 (60.8) 31 (19.6) 31 (19.6) Female 101 (56.4) 37 (20.7) 41 (22.9) 0.74 NS Pooled 197 (58.5) 68 (20.2) 72 (21.4) M. brevicornis Male 407 (41.9) 171 (17 .6) 394 (40.5) Female 523 (33.9) 213(13J-\) 808 (52.3) 33.34** Pooled 930 (37.0) 384 (15.3) 1202 (47.8) P. styl[fera Male I 02 (40.2) 74 (29.1) 78 (30.7) Female 84 (21.8) 96 (24.9) 205 (53.2) 36.25** Pooled 186(79.1) 170 (26.6) 283 (44.3) P. hardwickii Male 31(27.2) 42 (36.8) 41 (36.0) Female 64 (30.0) 49 (23.0) 100 (46.9) 7.39* Pooled 95 (29.1) 91 (27.8) 141 (43.3) P. sculptilis Male 56 (50.9) 25 (21.3) 29 (26.4) Female 68 (40.2) 36(21.3) 65 (38.5) 4.66 NS Pooled 124 (44.4) 61(2l.9) 94 (33.7) S. crassicornis Male 117 (60.0) 41 (21.0) 37 (19.0) Female 143 (44.1) 102(31.5) 79 (24.4) 12.54** Pooled 260 (50.1) 143 (27.6) 116 (22.4) p< 0.05*, p females was significantly more than Area-wise intensity of feeding of that of males in the case of P all the spegies together (Fig. 1) showed merguiensis (p<0.05), M. affinis that the -proportion of poorly-fed (p<0.05), M brevicornis (p Polychaetes 12.60% Foraminiferans Detritus 2.62% 7.75% Bivalves 1.92% ...... Acetesspp 29.93% ...... ~ ...... Prawn remains 25.40% Fig. 1: Composition of diet ofpenaeid prawns pooled together nearshore and offshore waters (Table 2) S. crassicornis (p Results Species Area Poorly fed Moderately fed Well Fed X) Inshore 40 (61.5) 12 (18.5) 13 (20.0) P. merguiensis Nearshore 78 (54.5) 38 (26.6) 27 (18.9) 1.77 NS Offshore 61 (55.5) 26 (23.6) 23 (20.9) Inshore 331 (56.9) 100 (17.2) 151 (25.9) M affinis Nearshore 258 (54.0) 118(24.1) 113 (23.1) 9.59** :< >=' Offshore 227 (54.0) 1:::} 98 (23.3) 95 (22.6) 0 Inshore 155 (76.0) 25 (12.3) 24 (11.8) M. monoceros Nearshore - - - 65.53** l ~ Offshore 42 (31.6) 43 (32.3) 48 (36.1) ' Vl Inshore 555 (58.1) 165 (17.3) 236 (24.7) Cll M brevicornis Nearshore 118 (24.0) 74 (24.0) 300 (61.0) 362.23** ~ ~ Offshore 257 (24.1) 145 (13.6) 666 (62.4) r- I Vl Inshore 46 (23.8) 52 (26.9) 95 (49.2) ~ I a:: P. stylifera Nearshore 94 (30.6) 87 (28.3) 126 (41.0) 5.96 NS I ~ Offshore 46 (33.1) 31 (22.3) 62 (44.6) I & Inshore 21 (27.3) 10 (13.0) 46 (59.7) ?> Vl P. hardwickii Nearshore 42 (31.8) 42 (31.8) 48 (36.4) 15.22** ~ Offshore 32 (27.1) 39 (33.1) 47 (39.8) ~ Inshore 61 (46.9) 28 (21.5) 41 (31.5) P. sculptilis Nearshore 63 (42.3) 33(22.1) 53 (35.6) 0.68 NS Offshore - - - Inshore 87(43.1) 53(26.2) 62(30.7) S. crdssicornis Nearshore 98(53.3) 52(28.3) 34(18.5) 14.33** Offshore 75(56.4) 38(28.6) . 20(15.0) p< 0.05*;p<0;0] **and NS Non-significant Table 3: Feeding intensity of mature and non-mature females from breeding areas s Results a'"i ...., Species Sex Poorly fed Moderately fed Well Fed (!) P"' x2 (!) § Non-mature 36 (56.3) 13 (20.3) 15 (23.4) p_.~ P. merguiensis Mature 29 (43.3) 20 (29.8) 18 (26.9) 2.44 NS (!) ~ &. 0 ~ Pooled 65 (49.6) 33 (25.2) 33 (25.2) ~(JQ I Non-mature 231 (54.0) 93 (21.7) 104 (24.3) s ..... z M affinis Mature 211 (56.7) 82(22.1) 79 (21.2) 1.10 NS a~ c~ '"i ~ 175 (21.9) 183 (22.8) (!) CZl ~ Pooled 442 (55.3) ..... r ~ ...... f""'t Non-mature 94 (64.8) 24 (16.5) 27 (18.6) (!) (]) CJ 7 13 (37.1) 15 s CZl ~ M. monoceros Mature (20.0) (42.9) 23.01 ** 0 e.o :;E"Tl Pooled 101 (56.1) 37 (20.5) 42 (23.3) (]) ~ CZl ~~ f""'t rnz Non-mature 145(17.5) 103 (12.4) 580 (70.1) ..... l:r' to;x:. ~ (]) C/l- M brevicornis Mature 93 (23.3) 44 (11.0) 263 (65.7) 5.77 NS orn "TJCJ Pooled 238 (19.4) 147 (12.0) 843 (68.6) CZl ~ $:;,'5 i:r'(l) C;x:. Non-mature 42 (21.3) 5 I (25.9) 104 (52.8) 0 ~ $::;E ~ ~ coz P. stylifera Mature 42 (22.4) 45 (23.9) 101 (53.7) 0.21 NS (]) l:r' ?CZJ o...o --z Pooled 84 (21.8) 96 (24.9) 205 (53.2) g.@ -l :r: ~§ rn Non-mature 31 (25.2) 24(19.5) 68 (55.3) n s p_. 0 P. hardwickii Mature 37 (30.8) 26 (21.7) 57 (47.5) 1.54 NS 0 0 ? 68 (28.0) 50 (20.6) 125(51.4) CZl Pooled ~~ ~ 0 l:r' r Non-mature 42 (41.6) 21 (20.8) 38 (37.6) ~0 f""'t-'"i 11 6 (20.0) 0.34 NS :::::r-(1) P. sculptilis Mature (36.7) 13 (43.3) (]) e; Pooled 53 (40.5) 27 (20.6) 51 (38.9) CZl (]) '"d ~ (!) CZl 107 (46.1) 70 (30.2) 55 (23.7) () ,---., Non-mature ...... , ( 42.5) 16 (20.0) 2.67 NS (]) ~ S. crassicornis Mature 36 (37.5) 34 CZl u Pooled 143 (45.0) 104 (32.7) 71 (22.3) ~~ - - -·····- - __ .....;...___- -- -- (!) \.;.) p_. "--" w *p< 0.05, **p< 0.05, NS Non-significant. --.] 38 V. D. Deshniukh, M.S. Sawant, S. J. Mane and A. S. Hule uniformly excepting M monoceros Table 4: Index of preponderence (0/o) (p (.,;.) N (.,;.) ...... (.,;.) No. of Vo N 0\ Vo -+:>...... -...l N (.,;.) ...... (.,;.) ...... \0 \0 0\ \0 -...l \0 00 specimens 35,------,J 0\ ...... examined m (.,;.) 00 N ...... g 30 N ...... -+:>. Vo N 00 N 0\ -...l v:; E (.,;.) i..o 00 ~ Vo ...... 0\ Vo Acetes spp. ~ 25 -+:>. (.,;.) \0 00 tv 0\ c -+:>. ~ 20 E ...... Vo -+:>. -+:>. (.,;.) ...... c. 15 (.,;.) -+:>...... \0 0\ -...l Vo (.,;.) 0\ ...... '"0 ...... \0 (.,;.) ...... -+:>. 00 Vo 00 0\ -...l \0 Prawn remains @ 10 "" '0 "" f ...... 0 0 ...... 0 ...... 0 0 'f...... 0 0 0 ~ 0\ -...l -+:>. -...l N N N -+:>. 00 N Cephalopods 0 0 0 0 0 0 -+:>. tv 0 0\ 00 0 0 \0 00 Vo -+:>. 00 \0 Vo 0\ ...... Gastropods ...... N N 0 0 0 0 0 0 (.,;.) -...l tv 0\ ~ ...... ~ (.,;.) Fig. 2: Comparison of diets between inshore Vo 0 (.,;.) 0 0 ...... -...l ...... Bivalves (stippled), nearshore (crossed lines) and ...... (.,;.) offshore waters (solid bars) -+:>. 0 N 0 -...l 0\ 0 00 ~ 0 tv ~ 00 -...l ...... Vo 0 tv Foraminiferans -+:>. -+:>. 00 0\ Vo N \0 (.,;.) N consisted of Acetes spp., prawn 0 \0 0 (.,;.) Vo Vo ~ 00 -...l ~ \0 tv ...... (.,;.) remains, polychaete s, benthic 00 (.,;.) -...l 0 (.,;.) -+:>. N ...... Polychaetes crustaceans, foraminifers and fish with 0 Vo ...... 0 0 (.,;.) 0\ 0 ...... ~ Benthic IP 29.93, 25.40, 12.60, 7.50, 7.75 and tv 0 00 \0 tv i..o ~ 00 00 0\ (.,;.) \0 crustaceans 5. 72, respectively. All the crustaceans 0 -+:>. (.,;.) ...... N 0 \0 Vo 0\ put together formed the propitious food ...... -+:>. ~ Vo \0 Vo \0 ...... 0 -...l ...... -...l (.,;.) -+:>. -...l Fish with IP of 63.08. Other food items and -...l their ponderal indices were: SDM -...l ...... 0 0 (.,;.) 0 00 ~ 0\ (.,;.) ...... 0 tv ...... ~ (3.61), detritus (2.62), bivalves (1.92), -...l 0 -...l 0 0\ 0\ ...... Sand/Mud (.,;.) (.,;.) (.,;.) 0 (.,;.) gastropods (0.55), cephalopods (0.44), \0 0\ 0 0\ ~ 00 Vo i..o Vo ...... unidentified matter (0.33), vegetable 00 (.,;.) ...... Vo -...l (.,;.) ...... SDM matter (0.06), and sand and mud (1.57). -+:>. -+:>. 00 ...... Vo ...... 0 ~ 0 0 ...... 0 Detritus -+:>. (.,;.) 0\ \0 Species-wise IP of the dietary 0 0 0 ...... 0 Vegetable 0 0 0 0 0 0 ~ 0 items pooled from different areas is 0\ Vo ...... N (.,;.) Matter given in Table 4. The comparison of 0 0 0 0 0 0 Unidentified ~ 00 Vo Vo 0 ...... 0 0 0\ 00 0 -...l -...l ...... matter NS: Not significant, *p < 0.05 NATURAL DIET OF PENAIED PRAWNS IN THE COASTAL 39 WATERS OF MUMBAI major food items between the species were significantly different (p<0.05). pooled from all the areas by Friedman's Comparisons of the dietary items between the sexes, maturity condition test Cl o.os. 8 = 19. 07) revealed that the dietary preferences between the species and areas by rank correlation are presented in Table 5. Table 5: Species-wise rank coefficients (rJ of dietary items between sexes, maturity condition and the areas Areas Maturity Species Sexes of females· Inshore- Inshore- Nearshore- Nearshore Offshore Offshore P. merguiensis 0.91 NS 0.62 NS 0.01 * 0.06* 0.55* M. ajjinis 0.83 NS 0.92 NS 0.65 NS 0.50* 0.58* M. monoceros 0.98 NS 0.59* ~ 0.30* ~ M. brevicornis 0.83 NS 0.92 NS 0.91 NS 0.81 NS 0.60* P. stylifera 0.86 NS 0.96 NS 0.77 NS 0.49* 0.72 NS P. hardwickii 0.78 NS 0.79 NS 0.79 NS 0.80 NS 0.78 NS P. sculptilis 1.00 NS 0.50* 0.70* ~ ~ S. crassicornis 0.81 NS 0.67 NS 0.30* 0.33* 0.78 NS NS: Not significant, *p < 0.05 Acetes spp. had the highest IP of with the IP of 12.60 was the third most 29.93 making it the most favourite food important food item but in offshore item, particularly in inshore water waters (28.27) it was the most preferred (30.53).Amongthe species, F. sculptitis item. It was the most favoured food for (81.43) and S. crassicornis (32.84) M. affinis (55.12), but formed sizeable favoured it most. Prawn remains were proportion in the guts of P. merguiensis the second most important item of food (25.31) andM. monoceros (23.24). with an IP of 25.4 but taken more in inshore (29. 7 6) waters. With IP of Benthic crustaceans had an IP of 51.15, 49.32 and 47.97, it was 7.5, but taken more in inshore (10.61) predominantly observed in P. and nearshore waters (10.76). It was the hardwickii, P. stylifera and M. predominant food of M brevicornis monoceros, respectively. Polychaetes (56.94). Foraminifers for all the species 40 V. D. Deshrnukh, M. S. Sawant, S. J. Mane and A. S. Rule together had aniP of7.75, which varied P. merguiensis from the maximum of 16.28 in M 50 affinis to the minimum of 0.84 in P sculptilis. Fish in all the species J.:J ll IO~~Jl =IIIIDIIilb"""' I together had an IP of 5.8, but M. monoceros appeared to prefer it more M.afflnis (9.3). Although IP for the bivalves and gastropods were only 1.92 and 0.55, respectively, bivalves were particularly :I ollfl ~ lllllli] -= llll I taken more in the nearshore waters (7. 78) and their presence in the gut ofP M. monoceros merguiensis was remarkable with an IP 1oo I of23 .31. The overall IP for cephalopods 0 1 ..... ll ..n ·- was low (0.44) though perceptibly more for P merguiensis (1. 72), M monoceros ~. brevicornis (1.44) and S. crassicornis (1.14) as 100 I compared to the other species. 0 llllfl IIIII= = lla:, -=" I Vegetable matter was rarely noticed in the guts ofprawns (IP 0. 06) except in M affinis (IP 1.5). Detritus was mainly P. sty/ifera seen in prawns which were poorly fed. 100 I The IP was 2.62 and found appreciably 0 ..0 ll OIIICJ ~--~ in the guts of P stylifera (IP 8.46), S. crassicornis (IP 4.54), M brevicornis P.scu/pti/is (IP 4.2), andP sculptilis (IP 4.13). 1~~ ~ ll - I Sex-wise diet: IP of the food items for the males and females of different P.hardwickii species is shown in Fig. 3. It was 100 I observed that the dietary composition 0 1110 ll -= I overlapped in the two sexes of all the species and the rank correlation S. crassicornis coefficients (rJ for the food items I (Table 5) ranged from 0. 78 to 1.0, which were high (p>0.05) enough to suggest ..OIIIII.:Jil., I .m:J~I1I I I I I I I I that the diets of the two sexes do not ~ln~.- ~ P. merguiensis in inshore, nearshore and offshore areas 2 by Friedman's test showed (X o.DI, 11 =29 .41) that the preference ofprawns to different food items is significantly M.affinis different (p M. brevicornis Inshore area: Acetes spp. (30.53%), prawn remains (29.76%), polycha~tes (9.14%), benthic crustaceans (10.61 %), fish (6.39%), M. monoceros foraminifers (3.68%) and molluscs (1.60%). For all the crustaceans 60 : together, theiPwas 70.90. "I n 13 ~ ".I. Nearshore area: Acetes spp. (22.54%), prawn remains (20.56%), polychaetes (11.39%), benthic crustaceans (10.76%), foraminifers (9.99%) and molluscs (8.94%). For all P. hardwickii the crustaceans together, the IP was 53.86. Offshore area: Polychaetes (28.27%), prawn remains (23.57%), Acetes spp. (14.61 %), foraminifers (9.84%), benthic crustaceans (6.66%) and fish (5.21 %). In this area, for all the crustaceans together, the IP was 44.84 but polychaetes were the single most S.crnsslcom/s 80 favoured food. 60 40 The comparison ofiP of the dietary 20 items of the individual species by correlation coefficients (rs) between Acatoa llpp Bonthlc G~:Jtropodn Fish Polychooto:~o t~nnd/mud Ootrltus inshore and nearshore, nearshore and Fig. 4: Comparison ofdiet ofspecies of offshore, and inshore and offshore prawns in inshore (stippled), nearshore waters showed (Table 5) that diet of P (crossed lines) and offshore waters (solid bars) merguiensis is significantly different (p<0.05) in all the three depth-zones. 42 V. D. Dcshmukh, M. S. Sawant, S. J. Mane and A. S. Hulc The species showed that prawn remains and polychaetes being the most desired were the preferred food item in inshore, food items in the two areas bivalves in nearshore and polychaetes respectively. ' in the offshore waters. In the case of M. brevicornis, the The dietary preference of S. food items were significantly different crassicornis was similar between between nearshore and offshore areas nearshore and offshore waters (r,.=0.60); in nearshore area the order of (rs=O. 78), but significantly different preference was benthic crustaceans, between inshore and nearshore waters prawn remains andAcetes spp., while in (rs=0.30), and inshore and offshore the offshore area, it was Acetes spp., waters (rs=0.33). Acetes spp. were the benthic crustaceans and fish. The diet in favourite food in inshore, and the inshore area was more or less the foraminifers in the nearshore and same as in the nearshore waters. offshore waters. P stylifera showed difference in M affinis showed that the dietary feeding preference between inshore and items are significantly different offshore waters (r.,.=0.49). Prawn between offshore and inshore (rs=0.50), remains and Acetes spp. were the and nearshore and offshore waters dominant food items in both inshore and (rs=0.58); polychaetes formed the most offshore waters, but the order of favoured food in all the three areas but preference of other food items was the sequential preference of the rest of detritus, fish and foraminifers in .the the food items was different, i.e., in former and foraminifers, polychaetes, inshore area, foraminifers, benthic detritus and gastropods in the latter crustaceans, fish and prawn remains areas. was the order of preference, while in offshore area, besides foraminifers and P sculptilis showed significant benthic crustaceans, Acetes spp. were difference between inshore and preferred by the species. In the nearshore areas (rs=O. 70), largely due to nearshore area, the preference was for the order of preference of the food prawn remains, benthic crustaceans, items: Acetes spp., prawn remains, detritus, Acetes spp. and fish. Thus, detritus and fish in the former, and polychaetes were the primary food in all Acetes spp., detritus and prawn remains the areas followed by the crustacean in the latter. · diet and foraminifers. Among all the species, P. hardwickii alone did not show any Although M monoceros could not difference between dietary items in the be obtained from nearshore waters, the three areas. The favoured items of food species clearly showed difference in were prawn remains, Acetes spp. and dietary preference in inshore and po lychaetes. offshore areas (rs=0.30), prawn remains NATURAL DIET OF PENAIED PRAWNS IN THE COASTAL 43 WATERS OF MUMBAI Maturity-wise diet: The composition of mature females of P sculptilis had first the diet of mature and non-mature preference toAcetes spp., but the former females presented in Fig.· 5 shows preferred fish to prawn remains as the significant variation in the case M next important food item and the latter monoceros (rs 0.59) and P sculptilis prawn remains to detritus. (rs=0.50) only. The mature females of M monoceros preferred polychaetes to DISCUSSION prawn remains, particularly in the offshore waters. Both mature and non- Williams ( 19 55) noted the association between the distribution of white shrimp and detritus-rich '~Bj,_------P.m-erg-uien---lsis.l. sediments in estuaries, and suggested j ""- r;ll= Kl • that there may be a species preference I for a particular type of substratum in which the availability of food is very l·u ,----~--- .....-ffi!II----'---M-. affi----jo;, I important. Dall (1968)commented that penaeid prawns feed on benthic micro- . fauna and therefore, the density of such benthic organisms would enable to estimate the abundance of prawns in any given area. The substrata of inshore, nearshore and offshore waters off Mumbai have been reported to be clayey silt (Parulekar et al., 1976; Varshney et al., 1988; Mathew and Govindan, 1995) with the proportion of sand increasing, and the biomass of meio-benthic and macro-benthic· P. hardwickii I organisms decreasing with depth. jl Quantitative investigations on benthic macro-fauna in Mumbai waters showed mean biomass of 4.47 g/m2 in inshore· (Mathew and Govindan, 1995), 6.82 g/m2 innearshore (Varshney et al., 1988; S.crassicornis Varshney and Govindan, 1995) and only 1.01 g/m2 in offshore waters (Parulekar et al., 197 6), which clearly indicate that the biomass of macro benthos is .the highest in the nearshore waters and relatively poor in the Fig. 5: Comparison ofdiet ofspecies of offshore waters. But, feeding intensity · prawns in non-mature (crossed) and of all the species pooled together mature (solid) females 44 V. D. Deshmukh, M. S. Sawant, S. J. Mane and A. S. Hulc showed (Fig. 1) that the prawns feed prawns do not simply graze at the better in offshore than inshore waters. bottom, but pick their food selectively. The higher feeding intensity and relatively poor standing stock of macro Selective feeding by the prawns benthos implies that the prawns must be can be further elucidated by considering grazing very intensively in the offshore the distribution and preference of the waters. Parulekar et al. (1976) opined food items. The biomass ofpolychaetes that the fluctuations in biomass of meio was the highest in all the three depth benthos in the offshore waters are due to zones; but excepting M. afjinis, the grazing by micro-benthos, but the prawns did not consume it impulsively present study indicates that the in the inshore and nearshore areas. fluctuations in biomass of both meio However, in the offshore waters, the and micro- benthos could be due to increased preference to polychaetes grazing by prawns. In the present study, was shown by almost all the species in M monoceros and M brevicornis general and M monoceros, M. affinis showed significantly higher feeding and P nzerguiensis in particular. The intensity in the offshore waters which importance of polychaetes in the diet consumed polychaetes and benthic suggests that the prawns select either crustaceans avidly. In this context, the tubicolous polychaetes by sifting the intensive feeding of mature M. mud or by hunting the errant species to monoceros females on polychaetes in meet their nutritional requirements. offshore waters is ofgreat significance. Benthic crustaceans formed second most important biomass in inshore The order of abundance of major waters, and the least in nearshore and macro-benthic organisms reported for offshore waters; yet these were the most the inshore waters was polychaetes, preferred food of M. brevicornis in all benthic crustaceans, foraminifers and the depth zones, which points out that molluscs (Mathew and Govindan, the species is selective and browses 1995); polychaetes, foraminifers, only on the interstitial crustaceans such benthic crustaceans and molluscs in the as amphipods, isopods, cumaceans and nearshore waters (Varshney et al., tanaidaceans. Although foraminifers 1988); and polychaetes, molluscs, was numerically the most abundant sipunculids, echinoderms, foraminifers group in all the depth-zones, it was the and benthic crustaceans in offshore second most preferred dietary item of S. waters (Parulekar et al., 1976). But the crassicornis and P stylifera in the preferences shown by the prawns were nearshore and offshore waters, and for not in accordance with the density or M. a./finis, in the inshore waters. Rao availability of these benthic food (1988) reported that the occurrence of organisms. Moreover, sipunculids and foraminifers in guts is due to accidental echinoderms reported in the offshore ingestion while browsing on the waters were not noticed in the guts of substratum, but substantial preference the prawns. This indicates that the of it by S. crassicornis and M. afjinis NATURAL DIET OF PENAIED PRAWNS IN THE COASTAL 45 WATERS OF MUMBAI alone rules out this possibility. The two waters from August to December and species must be exercising some sort of the latter during December-April choice to this food item in order to meet (Deshmukh et al., 2001 ), which their nutritional requirement. Bivalves obviates the competition between them. and gastropods did not form the bulk of the benthos, nevertheless they together Although individual species of formed the preferred food of P prawns exhibited diverse preferences to merguiensis in nearshore waters, which different food items, it . can be also suggests selectivity by the species. generalized that the prawns prefen·ed crustacean diet in both inshore and Interestingly, the epipelagic nearshore areas, and after migrating to shrimp Acetes spp. are not benthic; yet it the offshore area, changed over to was the primary food item of P polychaetes. It also emerges from the sculptilis (IP 81.43) and S. crassicornis study that these species are primarily (IP 32.43), which suggests that the two carnivorous and select different species are raptorial predators, organisms of their choice in varied swimming in the water column and proportions in different areas, which catching the moving prey. Though the may be advantageous to avoid predilection for prawn remains was competition for food among the observed in P hardwickii and P coexisting species. stylifera in all the zones, and in the juveniles of M monoceros in inshore ACKNOWLEDGEMENTS area, their presence in the guts may be due to scavenging on their own moult This work fonned pmi of the and eating newly moulted prawns that project funded by the Indian Council of can be termed effortless predation. Agricultural Research under AP-Cess Similarly, the incidence offish remains Fund. The financial support to the in the gut could be due to scavenging on Senior Research Fellows (MSS, SJM & dead fish larvae and juveniles. Since ASH) is gratefully aclmowledged. detritus was observed mainly in the guts of poorly-fed prawns, its presence in the REFERENCES guts of M brevicornis, P styl(fera, P sculptilis and S. crassicornis suggests Albertoni, E. F., Silva, C. P. and that it may be their emergency food Esteves, F. A., 2003. 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