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The harmful dinoflagellate, Heterocapsa circularisquama, has been causing mass mortalities of bivalve molluscs in Japan, at relatively low cell densities. Although several studies have been conducted to determine the toxicity mechanisms, the specific cause of death is still unclear. In a previous study, in our laboratory, it was shown that H. circularisquama (10(3) cells ml(-1)) caused extensive cytotoxicity in the gills of short-neck clams, Ruditapes philippinarum. In the present study, Mediterranean mussels, Mytilus galloprovincialis, were exposed to H. circularisquama at four cell densities (5, 50, 500, 10(3) cells ml(-1)), three temperatures (15, 20, and 25°C), and three exposure durations (3, 24, and 48 h), and the pathologies in nine organs (gills, labial palps, mantle, hepatopancreas, stomach, intestines, exhalant siphon, adductor muscles, and foot) were assessed. Foot, adductor muscles, and exhalent siphons of mussels were not affected; however, 16 inflammatory (hemocytic infiltration and aggregation, diapedesis, hyperplasia, hypertrophy, edema, melanization, and firbrosis) and degenerative (thrombus, thrombosed edema, cilia matting and exfoliation, epithelial desquamation, atrophy, and necrosis) pathologies were identified in the gills, labial palps, mantle, hepatopancreas, stomach, and intestines. The total prevalence and total intensity of pathology in each individual mussel, and the prevalence and intensity of pathology in each organ increased significantly with increased cell density, exposure duration, and temperature. The prevalence of pathology was the highest in gills, followed by the prevalence in labial palps, mantle, stomach, and intestines. Pathology was least prevalent in the hepatopancreas. The intensity of pathology was the highest in the gills, followed by the labial palps and mantle, the stomach and intestines, and the hepatopancreas. This detailed quantitative histopathological study demonstrates that exposure to H. circularisquama induces a broad cytotoxic effect in six vital organs, even at low density (5 cells ml(-1)) and low temperature (15°C), but not in muscular organs. Combining cell density, time, and duration of exposure, the organ most affected by the harmful alga was the gill, followed by the labial palps and mantle, the stomach and intestines, and the hepatopancreas. The results of this pathological analysis show that exposure to H. ciruclarisquama severely affects the gills, the labial palps, and mantle thereby interfering with particle clearance and sorting, cleansing, and respiration, but also affects the stomach, intestines, and hepatopancreas, altering the digestive processes and possibly detoxification pathways, if mussels are able to detoxify the toxins of H. circularisquama. In the most severe cases, bivalves would most likely have died as a result of combined severe alterations of the vital functions, failure of tissue repair, and moderate to heavy hemorrhaging in both the external organs and the digestive organs concomitantly with light to moderate alterations in the detoxifying processes.

In a laboratory study, we investigated the clearance rates (CRs), respiration rates (RRs), total hemocyte count (THC), pathological alterations, and mucocyte densities in the gills of the short-neck clam Ruditapes philippinarum when exposed to the toxic dinoflagellate Heterocapsa circularisquama. Within 2 h of exposure to H. circularisquama at a concentration of 5–103 cells/mL, both the CRs and the RRs were significantly decreased by 43–52% compared with the control CRs and 43–93% compared with the control RRs, respectively (ANOVA, Newman-Keuls, P < 0.05). Clams exposed to H. circularisquama at 103 cells/mL for 96 h showed a set of defensive and degenerative pathologies that were absent in control clams. Within 3 h, the gills exhibited cilia matting, followed within 24 h by heavy hemocytic infiltration in the connective tissue of plicae, distortion of filaments, hyperplasia, and fusion of adjacent filaments with matted cilia. Within 48 h, the gill plicae became contracted and showed multifocal ep...

The effects of the toxic dinoflagellate Heterocapsa circularisquama on the activity rate, development rate, prevalence of damage, and survival rate of trochophore and D-shaped larvae of the pearl oyster Pinctada fucata martensii were studied in relation to H. circularisquama cell densities and exposure duration. In addition, larvae were regularly processed via scanning electron microscopy to investigate morphological damage. The activity rate of both larval stages was significantly decreased after 3–6 h of exposure to H. circularisquama at densities ranging from 100 to 2 × 104 cells/mL. The prevalence of damage was significantly high after 3–6 h of exposure to H. circularisquama at densities of 100 to 2 × 104 cells/mL and 5 × 103 to 2 × 104 cells/mL for trochophores and D-shaped larvae, respectively. Cytoplasmic discharge, mass mucus production, irregular shape, delayed or inhibited mineralization of the shell, mantle protrusion, the appearance of abnormal masses in the velum, and the exfoliation...

The cephalopod receptor of particle motion was identified. In a previous study, it was suggested that statocysts served this function, but there was no direct supporting evidence, and epidermal hair cells had not been conclusively ruled out. Experiments on Octopus ocellatus were conducted using respiratory activity as an indicator of sound perception. Intact animals clearly responded to 141-Hz particle motion at particle accelerations below 1.3 ¥ 10 -3 m/s 2 , and the mean perception threshold at this frequency was approximately 6.0 ¥ 10 -4 m/s 2 . Specimens in which the statoliths had been surgically removed did not show any response for accelerations up to 3.9 ¥ 10 -3 m/s 2 at 141 Hz, which was approximately 16 dB greater than the mean perception threshold at this frequency. Specimens that had undergone a control operation in which the statoliths remained intact showed positive responses at 2.8 ¥ 10 -3 m/s 2 for the same frequency stimulus. This indicates that the statocyst, which is morphologically similar to the inner ear system in fish, is responsible for the observed responses to particle motion in O. ocellatus. This is the first direct evidence that cephalo- pods detect kinetic sound components using statocysts.

To explore behavioral responses to sound and the detectable frequency range of Octopus ocellatus, responses of the octopus to 120 dB rms sound stimuli of various frequencies were observed. The octopus did not respond at 200-1000 Hz, but clearly responded at 50-150 Hz by showing lengthened respiratory activities. Their respiratory activity was frequently suppressed for more than 5 sec after the sound stimulation, and the longest respiratory suppression reached 55.6 sec, while the mean respiratory activity length without sound stimulation was 1.23 sec. In the case of long-lasting respiratory suppression, they retracted the basal parts of their eyes simultaneously. This suggests that underwater sound may play an important role in the life of the octopus, possibly to detect predators.

Post-hatching development of the brain in the oegopsid squid, Todarodes pacificus was described using conventional histological and Cajal's silver impregnation methods. The oegopsid squids spend a specific paralarval period before attaining adult-like juveniles. In the just-hatched paralarvae, the brain lobes (lower and intermediate motor centers) are differentiating only in the ventral part of the brain (subesophageal mass, SBM), and development of the dorsal part of the brain (supraesophageal mass, SPM) shows a heterochronic delay. In the SPM, an arched bundle of axonal tracts (transverse arch, TA) crosses the region over the oral ingrowth. In the early paralarval period, the basal lobes and precommissural lobe (higher motor centers) begin to develop along the TA. A little later, a pair of longitudinal axonal tracts (supraesophageal ladder, SPRL) elongates anteriorly from the TA, and accessory lobes (centers for memory and learning) and superior buccal lobes begin to differentiate along the SPRL. In the mid paralarval period, the lobes of the olfactory center and the peduncle lobe develop well in each optic tract region. In the late paralarvae, all brain lobes become identifiable and the brain shows substantially the same organization as that in the adults. The dorsal-most region of the SPM largely increases in volume with striking growth of the accessory lobes. The SBM elongates in anterior and posterior directions and the rostral end (anterior SBM) separates from the middle SBM. The optic lobes become very large with neuropils arranged in layers. In the juveniles, the neuropils increase in relative volume to the perikaryal layers, and neuronal somata enlarge markedly in some lobes. The retarded development of higher motor centers during paralarval development suggests that the early paralarvae of T. pacificus are not active predators but suspension feeders.

Early ontogeny of the Japanese Common Squid Todarodes pacificus was described for artificially inseminated and collected specimens to present new criteria for developmental stages in relation to its ecological adaptation. For the purpose, details for formation of the following organs and tissues were observed with special attention: cilia on the integument, mouth part, shell sac and stellate ganglia, visceral mass, funnel-collar complex, statocysts, eye parts, and ventral photosensitive vesicles. At the embryonic stage (i.e., pre-hatching), various types of epidermal cilia that seem to work as the embryonic rotation were detected. At the early postembryonic stage (i.e., post-hatching), the epidermal lines were characteristically arranged at the scattered condition on arms, tentacles, head, and funnel. Novel strong muscle fibers were distinct in the base of tentacles and funnel retractor muscles at the early postembryonic stage, which is clearly related to the head withdrawal behavior of the paralarvae. The lip cilia and toothed beak developed at the early postembryonic stage, but disappeared later; these apparatus were considered to be related with a change of unique feeding mode in the paralarval life. Based on such morphological features, four distinct stages, namely, paralarval stage 1, 2, 3, and juvenile stage are proposed. The present observations are discussed in relation to survival strategy at early life of T. pacificus and they are compared with those in other cephalopods.

An atlas of the developing brain up to hatching stage is established using conventional histo-logical methods in the oegopsid squid, Todarodes pacificus. The brain originates from placodal thickenings in the ectoderm at the end of epiboly. The neuroblasts composing the placodes ingress in a group and accumulate into ganglia under the proximal surface of the surface epithelium. Four pairs of the ganglia, pedal, palliovisceral, cerebral, and optic, form the brain primordium. These ganglia come into contact with one another, and eventually accumulate into a ring-like cluster (circumesophageal cluster) encircling the oral ingrowth and the inner yolk around the surface of the head. The circumesophageal cluster regionally differentiates into brain lobe anlagen through formation of neuropiles and nerve tracts. The neuropiles form a ladder-like structure with two longitudinal columns situated in the ventrolateral parts of the circumesophageal mass and some axonal tracts bridging the left and right column...

The embryonic development of the central nervous system (CNS) in the oval squid Sepioteuthis lessoniana is described. It has three distinct phases: (1) The ganglionic accumulation phase: Ganglionic cell clusters develop by ingression, migration, and accumulation of neuroblasts. (2) The lobe differentiation phase: Ganglia differentiate into lobes. The phase is identified by the beginning of an axogenesis. During this phase, neuropils are first formed in the suboesophageal mass, then in the basal lobe system, and finally in the inferior frontal lobes and the superior frontal-vertical lobe systems. (3) The neuropil increment phase: After the shape of the lobes reached its typical form, neuropil growth occurs, specifically in the vertical lobe. The paralarval central nervous system (CNS) is characterized by neuronal gigantism of the giant fibers and some suboesophageal commissures and connectives. The neuropil formation in the CNS of S. lessoniana occurs somewhat earlier than in Octopus vulgaris, although the principal developmental plan is quite conservative among the other coleoids investigated. Some phylogenetic aspects are discussed based on the similarities in the morphologic organization of their brains. J. Comp. Neurol. 437:449–475, 2001. © 2001 Wiley-Liss, Inc.

Bioaccumulation of cadmium (Cd) by oval squid, Sepioteuthis lessoniana, the relative contributions of Cd in water and food to bioaccumulation, and the distribution of cadmium among organs were studied. In a bioconcentration test, oval squid was exposed to 0.2 mg Cd/l seawater for 14 days, then was reared in Cd-free seawater for 14 days. After the exposure and elimination periods, the Cd concentrations in the whole body were 3.10 ± 0.18 and 1.90 ± 0.05 μg/g wet weight (ww), respectively. The bioconcentration factor (BCF) was 15.5 after exposure for 14 days. The liver exhibited the highest Cd concentration ( 49.3 μg / g ww), and had the highest proportion of organ Cd content (42.8%) to whole-body burden at the end of the exposure period. In a biomagnification test, oval squid was exposed to 0.12 mg Cd/l seawater for 15 days and was simultaneously fed mummichog, Fundulus heteroclitus, that were simultaneously exposed to the same Cd concentration. For a further eight days the squid was kept in Cd-free seawater and was fed mummichog that were also kept in Cd-free seawater. After the exposure and elimination periods, the Cd concentrations in the whole body were 4.18 ± 0.69 and 2.80 ± 0.44 μg/g ww, respectively. The concentration of whole-body Cd in the oval squid that was derived from water was estimated at 1.86 μg / g ww after calculation of a BCF from the bioconcentration test. The contribution of Cd derived from water to the whole-body Cd burden appeared similar to that of the Cd derived from food. In the biomagnification test, the liver Cd concentration ( 58.8 μg / g ww) and its proportion of the whole-body Cd concentration (40.6%) were the highest among those of all the organs after exposure for 15 days, regardless of the uptake route. Because wild squid seem to be exposed to much lower Cd concentrations in water and are subjected to similar Cd concentrations in their prey, compared with squid of the present study, the main Cd source for squid would appear to be dietary.

Summary Oocyte development in the small penaeid shrimp Metapenaeopsis dalei was studied histologically. Seven stages were distinguished, namely (1) oocytes 10μm in diameter are strongly basophilic and spherical, (2) weakly basophilic ooplasm appears around the germinal vesicle, (3) follicle cells appear, (4) lipid globules appear in the ooplasm, (5) yolk granules start to appear in the ooplasm, (6) the germinal vesicle shrinks and migrates marginally, (7) the follicle cells disappear. This is the first report of a fully matured penaeid oocyte without cortical crypts which release materials forming a jelly coat when the eggs are exposed to seawater. Since ovulated oocytes occur in the same section of the ovary as earlier stages, M. dalei is concluded to be a multiple spawner which has short spawning intervals.

Batissaviolacea Lamarck (l806) locally known as “cabibi” is considered endemic in Cagayan River at Lallo, Philippines and the most expensive freshwater bivalve in the region. This study described through monthly histological examination the cytological characteristics of gametogenesis and sexual dimorphism of the gonad of B. violacea collected from the wild, and determined spawning response using serotonin. Eight category sizes of the species were established, and 10 samples from each size were processed. Gonads were preserved, and subjected for histological processes to confirm gametogenesis. Using descriptive data analysis, confirmation of the identified mature stage at 31-35 mm was further tested through induction of serotonin. Results showed progressive stages of sperm formation in male follicles. Follicles could be seen in clusters and identified as to their sizes from spermatogonia, spermatocytes, spermatids and spermatozoa. Growing female follicles appeared attached to a cytoplasmic stalk in different sizes and shapes. Initially male germ cells appeared tiny and became concentrated at the lumen in radiating bands as they become mature. Likewise, mature oocytes with enlarged nucleus and tiny nucleolus fill the center of the lumen of the female gonad was observed. B. violacea successfully spawn using either 0.2 ml or 0.5 ml earlier (0.21 hour) compared to 36.70 hour when no injection was administered. This is a first time report in the country along the possibility of breeding the species in captivity.Keywords: Aquatic ecology, Batissa violacea, gametogenesis, Cagayan River, induced spawning,experimental design, Cagayan river

Oxygen consumption rates of the young oval squid Sepioteuthis lessoniana (0.033-27.54g BW) reared from eggs and those captured from wild population were investigated on an individual basis by both water bottle and flow-through methods. Oxygen consumption rate (R in ml oxygen/ind./h) increased linearly with increase in BW (W in g) expressed as R=aWb. For squid smaller than about 2g BW, there was not a significant difference in the values of the exponent b and the coef-ficient a between R's measured respectively by water bottle and flow-through methods. The R was not significantly different from each other between squid reared from eggs and captured from the sea. The exponent b and coefficient a for young squids ranged from 0.741 to 0.944 and from 0.697 to 0.966, respectively. There was a tendency for the exponent to change with growth, such as b for the squids less than 0.5g BW being 0.944, while for the squids over 0.5g was 0.813, respec-tively. This suggests that R in very early life stage tends to increase more rapidly with growth than in older stages.