BEIIAVIOLIR of Jiwenile CEPIIALOPODS: PREFERENCE for TEXTI,]RE AI\D BRIGIITNESS of SI.]BSTRA

$BEIIAVIOLIR of Jiwenile CEPIIALOPODS: PREFERENCE for TEXTI,]RE AI\D BRIGIITNESS of SI.]BSTRA$ Phuhet Marine Biological Center Special Publication 21(1): 103-112 (2000) 103 BEIIAVIOLIR OF JIwENILE CEPIIALOPODS: PREFERENCE FOR TEXTI,]RE AI\D BRIGIITNESS OF SI.]BSTRA. TA Jaruwat Nabhitabhata & Pitiporn Nilaphat Rayong Coastal Aquaculture Station, Ta-pong, Changwat Rayong 2100, Thailand. ABSTRACT strata is referred to as epipsammon (on Behavioural preference for different types and sand) or epipelos (on mud). An important levels of brightness of substrata was studied in property for the inhabiting animals is the cultured, juvenile sepiid cuttlefish, Sepia suitability to move upon and to burrow in pharaonis and Sepiella inermis. Sand, muddy the soft substrata. Substrata affect metabo- sand and mud represented types ofbenthic sub- lism and activity of the animals via their stratum. Both species ofcuttlefish preferred sand physico-chemical properties, particularly to mud in long term studies (24 hrs). White, grey and black plastic plates were used as substrata their resistance to animal activities such as representing high, medium and low levels of Iocomotion, respiratory ventilation, and bur- brightness. The cuttlefish preferred medium level rowing in benthic cephalopods. Exposure ofbrightness during the early phase (up to 3 hrs) and water movement influences properties of the experiment. The degree of preference for of soft substrata. Therefore, habitat selec- substratum was higher in Sepia, living in the tion of aquatic animals is essentially the re- open sea, compared to the estuafine Sepiella. Iationship between behaviour and environ- Cuttlefish selected substrata in relation to ben- ment (Meadows & Campbell 1972). The ani- efrts, which we suggest are facilitated respira- mals are not able to differentiate between tion, crypsis, and energy conservation. Cultured bigfin squid, Sepioteuthis lessoniana, was stud- every variable they encounter in their erivi- ied as an outgroup on preference for brightness ronment. Meadows & Campbell(L972) corn- ofsubstrata. The bigfrn squid preferred medium mented that few animals are known to show level ofbrightness during the first 6 hrs and then lack of preferences. The preference may al- gradually changed to prefer low level of bright- ter depending upon physiological state as ness at night. We suggest that preference for well as previous experience and learning. brightness is associated with visual discrimina- The behavioural preference of individuals performing in- tion of depth in the pelagic squid may vary in rather unexpected ways but nate diurnal migration to greater depth. The preference species recognisable present results should be applied to painting of a has a cephalopod culture tanks in order to reduce pattern. Closely related species living in the stress, promote grou'th and enhance the contrast same environment have different habitat of feed. preferences but changes in physiolory associated with preference are very little known. INTRODUCTION Cephalopods lie, burrow and attach to sub- The term "substratum" refers to structures strata. Hence, the type ofsubstratum affects to which organisms in question maintain, the behaviour of cephalopods in several temporarily or permanently, a close contact ways, e.g. in ritualised behaviour, in am- and does not include aquatic or nutritive bushing, and sheltering (crypsis, camou- media (Gerlach 1972). Animals may move flage). Most cephalopods can adjust the ap- on, o attach to the surface ofsolid substrata pearance of their bodies to match different called epilithion. The surface of soft sub- substrata. Female cephalopods attach their 704 Tlopical Marine Mollusc Programme (TMMP) egg capsules to various types of substrata; countering any types of soft substrata in sponge, coral, seaweed, and rock. The Thai order to avoid learning behaviour. pygmy squid, Idiosepius thq.ilondicus, ad- The bottom ofeach glass aquarium (35 x heres to seaweed fronds in ritualised behav- 60 x 36 cm) was divided into 3 sections. Each iour, in mating behaviour, and for transpor- section was randomly spread with one of the tation when the seaweed turns into a float- three types of substrata, sand, sandy mud ing substratum (Nabhitabhata 1998). and mud. One glass aquarium represented The eyes ofcephalopods are excellent and one replicate. The soft substrata had been have a structure and function comparable collected from Changwat Rayong, Thailand. to those of higher vertebrates, but The sandy mud was a mixture of collected cephalopods are colour-blind (Messenger ef sand and mud at the ratio of 1:1 by volume. aL.1973, Roffe 1975, Messenger 1977, Flores The trial consisted of 8 tests, each with 3 et al. 7978). However, they able to distin- replicates (24 replicates in total) for spine- guish the level of brightness (Messenger & less cuttlefish. For the pharaoh cuttlefish, Sanders 7972) and,the plane ofpolarisation the trial consisted of2 tests, one test with 3 of the substrata and other objects (Wells replicates and another with 2 replicates (5 1966). The retina of the cephalopod eye may replicates in total). Ten cuttlefish were re- possess a system for detection ofwavelength leased into one aquarium (replicate) and (Messenger et al. 7973). Different colours then the numbers of lying and burrowing appear as different degrees of brightness cuttlefrsh on each type of substratum were contrasting against the surrounding back- counted and the behaviour were observed. ground on a grey scale. Messenger & Sand- The observation from initial time lapse was ers (1972) reported that the eyes of Octopus at 0.05,0.15, 0.30, 0.45, 1.00, 1.30,2.00, 3.00, uulgaris were able to discriminate bright- 6.00, 9.00, 12.00, 18.00 and 24.00 hrs. The ness better than orientation ofshapes. Young time interval was 5, 10, 15, 15, 30, 60, 180, (1968) found that octopus tended to attack 180, 360 and 360 min respectively. Signifi- black objects more often than white ones if cance was tested by chi-square test at 95 Vo appearing against a white background. Such (P < 0.05) and at 99 7o (P < 0.01) for each difference was not present with a grey back- observation of the test. grou.nd. The appearance ofthe objects to the During the tests, water parameters were cephalopod eyes partly depends on the con- monitored every 6 hours. Water tempera- trast ofthe object against the surrounding ture, pH and salinity were determined by background. mercury thermometer, pH meter (HANNA electric paper) and refractometer (ATAGO MATERIALS AND METHODS S-10) respectively. Average temperature re- Soft substrata (terture) corded was 28.2 + 0.6 oC, average pH was The experimental cuttlefish were reared 8.0 t 0.1 and average salinity was 30 + 2 from hatchling tojuvenile at the age ofabout ppt. 30 days. The average size of the pharaoh cuttlefis[ Sepia pharaonis,was 3.68 t 0.33 Solid s ub strata ( b rightnes s) cm in mantle length and 8.67 + 2.79 g in The experimental cephalopods were reared weight. The average size of the spineless from hatchling to juvenile at the age of about cuttlefrsh, Sepiella inerrnis,was3.22 t 0.16 20 days. The rearing methods followed cm in length and 6.53 + 0.85 g in weight. Nabhitabhata (1978a,1996) for the bigfin The rearing method foliowed Nabhitabhata squid, Sepioteuthis lessoniana, and as pre- (1978b) and Nabhitabhata et al. (1984) re- viously mentioned for the other two species spectively. The animals were reared in con- of cuttlefish. The pelagic bigfrn squids were crete tanks and had no experience on en- tested as an outgroup for comparison. The Phuhet Marine Biological Center Special Publication 21(1): 103-112 (20OO) 105 rearing tanks were painted sky-blue consid- licates for each species ofcephalopod. In each ered as neutral brightness in order to avoid replicate, the animals used were 24 pharao learning behaviour. The average size ofthe cuttlefish, 9 spineless cuttlefish, and 12 bigtin squids was 1.75 t 0.15 cm in mantle bigfin squids respectively. Other details as length and 1.20 t 0.34 g in weight. The av- well as water quality were the same as men- erage size of the pharaoh cuttlefish was 0.85 tioned for soft substrata. + 0.06 cm in length and 0.45 + 0.11 g in weight and of the spineless cuttlefish was RESULTS 1.35 t 0.18 cm, 0.85 t 0.27 g. Tnxr:uno oF sUBSTRATUM The bottom of each glass aquarium (35 x (sorr suesrRArA.) 60 x 36 cm) was divided into 3 sections. Each section was randomly spread with one of the Pharaoh cuttlefish, Sepia pharaonis three plastic plates ofwhite, grey or black Preference for mud dominated signifrcantly in colour representing the high, medium and over other substrata (P < 0.05) in the first low level of brightness respectively. One 15 minutes (Table 1) but after that the de- aquarium represented one replicate for the gtee ofpreference decreased to non signifi- cuttlefish test. The test for bigfrn squid was cant difference until 1.30 hrs (P > 0.10-0.35). held in circular concrete tanks of 1.50 m di- The preference increased to significant dif- ameter with 60 cm water depth. One tank ference again (P < 0.025) until 3.00 hrs. In represented one replicate for the squid test. nighttime through the daytime of the next Plastic plates of the three colours were ran- day (24.00 hrs), the preference for sand and domly and in equal numbers spread on the mud were not different (P > 0.05) but sig- tank bottom. nificantly different (P < 0.05) from sandy The trial consisted of one test with 3 rep- mud substratum. The highest degree of pref- Table 1. Pharaoh cuttlefish, Sepia pharaonls. Test ofpreference on type ofsubstratum. There were 50 individuals in this trial. N = the number ofcuttlefish lying on substrata (swimming cuttlefrsh were excluded). *, x* indicate signifrcant difference (P < 0.05, 0.01) respectively; a,b,c indicate significant range difference (P < 0.05) as different consonants; n = nighttime; ns = non significant difference 1P > 0.05); x = maximum frgure.

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