The interactions between beaugregory damselfish and ophiuroids, potential damselfish egg predators, were investigated using several field studies. A survey of back reef areas showed that the two most common ophiuroid species, Ophiocoma echinata and Ophioderma appressum, were significantly associated with the territories of beaugregory males within the coral rubble habitat where both ophiuroids and beaugregory's can be found. Feeding experiments showed that three ophiuroid species (Ophiocoma echinata, Ophioderma appressum and Ophiocoma wendtii) and Echinometra viridis consumed late development stage beaugregory eggs, whereas earlier stages were only consumed by Ophioderma appressum and Echinometra viridis. Manipulation of ophiuroid densities had no significant effect on the survival of beaugregory eggs and had no measurable impact on female mate choice. The aggressive response of male beaugregory damselfish towards three ophiuroid and one echinoid species showed significant differences among species but were lower than those shown to bluehead wrasse, Thallasoma bifasciatum; the principal daylight predator of eggs. The intensity of attacks by male beaugregory damselfish towards Thallasoma bifasciatum increased significantly if males were guarding eggs, but did not appear to change for the four echinoderm species. Male habitat selection was shown to be unaffected by the presence of ophiuroids.

The influence of circulation on abundance patterns of larval fish was compared at different phases of the tide in the vicinity of an estuarine front in Corral Bay, Chile during austral spring. Greatest differences in water salinity were found across the frontal region on ebb tides. Because rainfall was low, density differences were primarily due to tidal intrusion of salt water. Larval density was relatively low during both sampling periods with Strangomera bentincki, Oodntesthes regia laticlavia, Gobiesox marmoratus and Hypsoblennius sordidus as the most abundant species. Total ichthyoplankton was always higher near the tidal front (Stations 2 and 3). Spatial distribution in relation to tidal phase showed different patterns for the most abundant fish larval species. Circulation and larval distribution revealed that the bay was a source of young fish larvae but older individuals could also be recruited in and retained there. Results show that the front could act as a physical boundary for larvae transported from offshore through specific mechanism of circulation related with the tidal regime.

The growth patterns of juveniles of Solea solea and Solea senegalensis were compared, within the nursery areas of the Tagus estuary. Growth was estimated by modal progression analysis of length–frequency data, using the Bhattacharya method based on 1327 and 3255 individuals of S. solea and S. senegalensis, respectively. For the two species several cohorts of the same age-group were identified, being the number relative to S. senegalensis higher compared to S. solea. 0-group individuals of S. solea begin to occur within the nursery in May, while for S. senegalensis the recruitment is longer (from June to October). The number of individuals of the first cohort was higher relative to those belonging to the subsequent cohorts. The growth rate of S. solea juveniles varied from 0·01 mm d−1 to 1·51 mm d−1 and that of S. senegalensis was between 0·22 mm d−1 and 0·89 mm d−1. Although no significant differences were found when comparing growth rate values determined for the different cohorts, age-groups and species, it was noticed that the estimates determined for cohort I were generally higher at the beginning of the nursery colonization period. The differences in the seasonal variation of growth rate of S. solea and S. senegalensis reflected their spawning behaviour and time spent in the plankton and also their differential habitat use pattern.

The morphology of the cells during oogenesis in Amiantis umbonella (Mollusca: Bivalvia) was investigated from collections made between November 1997 and January 1999. Each stage is described and prominent features noted. A unique arrangement of auxiliary cells around the oocyte is described.

The sound characteristics and the sound producing system in silver sweeper, Pempheris schwenkii, are described. The main frequency component of the emitted sounds was 100–300 Hz, the mean duration of the sounds being 56 ms. The sounds were produced by paired extrinsic sonic muscles vibrating the swimbladder. The sonic muscles originated on the pterotic bones and extended to the anterodorsal surface of the swimbladder, and were innervated by two branches of the occipital nerves. Moreover significant sexual dimorphism of the sonic muscles was observed, those in males being three times as large as in females.

The olfactory organs in juvenile Dascyllus aruanus and Amphiprion ocellaris, studied by scanning and transmission electron microscopy (SEM and TEM), consisted of two bilaterally radial rosettes per specimen, fan-shaped, located medio-ventrally, one in each of two olfactory chambers. In D. aruanus the rosette comprises six lamellae, three on each side of a midline raphe; in A. ocellaris 12 lamellae, six on each side. In both species, the sensory regions in the lamellae are continuous, except for the margin of the lamellae, and richly covered with stereocilia. Areas with juvenile bipolar receptor cells were observed in both species. Two dissimilar types of olfactory receptor cells in the sensory epithelium: ciliated and microvillous were observed.

Ontogenic change patterns in otolith Sr:Ca ratios in the threespine stickleback, Gasterosteus aculeatus, collected from Japanese brackish waters and freshwater, were examined by wavelength dispersive X-ray spectrometry on an electron microprobe. Two-dimensional images of the Sr concentration in the otoliths showed a variety of patterns of Sr concentration relative to salinity of habitat in all specimens collected in Hokkaido Island. Otolith Sr:Ca ratios in line analysis of all specimens collected in Hokkaido Island fluctuated strongly during the life history transect in accordance with the migration (habitat) pattern from sea to freshwater, via brackish water. In contrast, the Sr concentration or the Sr:Ca ratios of the Otsuchi River stickleback remained at consistently low levels throughout the otolith (1·5×10−3 in the Sr:Ca ratios). The higher ratios (3·2–6·3×10−3) in sticklebacks collected in Hokkaido Island probably reflect the ambient salinity or the seawater–freshwater gradient in Sr concentration. The findings clearly indicated that otolith Sr:Ca ratios reflected individual life histories, and that the stickleback had a flexible migration strategy in the ambient water.

Big-bellied seahorses, Hippocampus abdominalis (Chordata: Syngnathidae), feed predominantly on swarming mysids in southern Tasmania. We tested the possibility that kairomones mediate this predator/prey interaction. ‘Fish water’ was prepared by holding one seahorse in 4 l of seawater for 1 h and using this water within 1 h to test for presence of kairomones. One ml of this water pipetted into a tank containing five mysids, Paramesopodopsis rufa (Arthropoda: Mysidacea), induced a significantly increased number of tailflips (mysid escape response) compared with control seawater. The same effect was seen whether seahorses were fed or starved immediately before the experiment. This effect was not seen when realistic concentrations of excretory products, either ammonium hydroxide or urea, were used instead of fish water. When seahorses were kept in visual contact with mysid prey, but unable to capture them, subsequent testing of the ‘fish water’ in the same way as above did not produce a significant increase of tailflipping in mysids. Thus it appears that, when attacking, seahorses can suppress release of kairomones in order to remain chemically inconspicuous to their prey. This is the first demonstration of this phenomenon. When mysids in a cohesive swarm (65 or 100 individuals) were exposed to ‘fish water’, no significant anti-predator response i.e. decrease in swarm volume, could be detected. We interpret these results to indicate the greater vulnerability of mysids when not in social groupings (swarm or school) and the higher likelihood of an energetic response (particularly tailflipping) to a threat.

This paper reports the occurrence of the fifth species of Mobula in the western Atlantic, M. thurstoni, based on specimens caught by artisanal and driftnet fisheries in coastal waters off southern Brazil.

Spatial distribution of the southernmost population of the purple clam, Amiantis purpurata (Bivalvia: Veneridae), was described from systematic survey data (density and local biomass), and was related to environmental variables (depth and sediment). Geostatistical techniques were used to model and map density, and to estimate absolute biomass.

Spatial distribution was highly contagious: half of the population lives at densities up to 240 clams m−2. Higher clam abundance occur only at sites with finer and well sorted sediment and intermediate depth. Even when the demographic structure of the population was composed of three year-classes recruited between 1978 and 1980, local biomass and density exhibited a non-linear relationship between them, and discrepancies between their distributions of frequency, their relationship with depth, and variographic analysis.

The spherical model was fitted to the experimental variograms. Anisotropy was explored and introduced into the model. The resulting map shows the location and extension of the patches in the study area; they conform a fringe where the highest concentrations are oriented parallel to the coast line, interrupted by small shoals. No anisotropism was evident in the variographic analysis of local biomass. The kriged mean was 3369 g m−2; and estimated total biomass was 53,290 tn.

Such differences between density and local biomass seem to be linked to compensatory processes involving biomass, growth and mortality, originated at the scale of individual overlapping neighbourhoods.

Like their counterparts at lower latitudes, many Antarctic midwater fish make extensive, diel vertical migrations. However, Antarctic species make these migrations in the absence of two of the three selective advantages generally ascribed to this behaviour. Because the water column is nearly isothermal, there is no metabolic bonus to be gained from thermal differences in habitat depth. Likewise, because their prey do not perform significant vertical migrations, the fish migrations act to diminish rather than enhance their feeding opportunities. For Antarctic midwater fish, the sole advantage of these migrations appears to be the avoidance of visually-cued predators in the upper part of the water column. An evaluation of the relative importance of the three selective factors supports the suggestion that predator avoidance may also be the principal driver of diel vertical migrations for midwater fish at lower latitudes.

The relation of moisture content, temperature, nest depth, incubation, distance from sea and vegetation to hatching success of loggerhead sea turtles, Caretta caretta, in Turkey was studied. Nineteen randomly selected clutches were examined. Moisture was found to be negatively correlated with distance from the sea (P<0·05) but positively correlated with temperature (P<0·01). Temperature was negatively correlated with incubation time. Hatching success was not correlated with any of the environmental factors examined.

An immunological technique has been developed, which discriminates the Pecten maximus larvae among all other species present in different plankton samples from Brest Bay. This tool was used on each plankton sample to target the temporal distribution of the larvae between summer 1997 and summer 1998. The least abundant period for larvae from April to July 1998, was confirmed and also identified P. maximus which would have been very difficult to recognize with only the help of the analysis of prodissoconch shape. Multi micro-cohort larvae principally from April to July 1998 corresponded probably with as many spawning events.

Histological analysis was used to describe and analyse the process of ovarian atresia in sardine (Sardina pilchardus sardina) from the central Aegean Sea (eastern Mediterranean). The spawning potential of females in relation to intensity of atresia was evaluated and the rate that the ovary passed from the active to inactive condition was followed in fish collected over an annual cycle. Early postspawning females, defined as those with 100% alpha-atretic oocytes, occurred throughout the spawning period; they had lower gonosomatic and hepatosomatic index, but similar total length compared to reproductively active females.

A roughtail stingray, Dasyatis centroura, and a spiny buterfly ray, Gymnura altavela, were caught near Kolocčep Island (Elafiti Archipelago, southern Adriatic) and the settlement Crkvice (Pelješac Peninsula, southern Adriatic) in October 2002 and November 2000, respectively. The roughtail stingray is the largest specimen recorded. Morphometric data of spiny butterfly ray are the first for this species in the Adriatic Sea.

Investigations conducted off the Algerian coast between 1996 and 2001 resulted in the collection of 201 blue sharks, Prionace glauca, including 144 females and 57 males. Prionace glauca is mainly captured off the central area and lesser in the eastern area from the Algerian coast. The central area is probably a mating site of the species. The sex ratio changes are calculated according to specimen sizes and seasons. The recent abundance of the species in Mediterranean areas is discussed.

This study reports the age estimation of marine tucuxi dolphins (Sotalia fluviatilis) found dead along the south-east coast of Brazil (24°40′S–25°30′S). The investigated specimens were collected from August 1995 to December 1998. Ages were estimated through the number of Growth Layer Groups (GLGs) from decalcified and stained thin sections of teeth. A total of 36 individuals was investigated. Estimated ages of marine tucuxis varied from zero to 29 years. The growth curve was attained from a modification of the von Bertalanffy equation applied to body length and age data. It was possible to estimate the total length of 97·8 cm in newborns, physical maturity was attained at seven years of age, and an asymptotic length of 179·8 cm.

Two species of bivalves, Cerastoderma glaucum and Abra Ovata, typical inhabitants of brackish waters, were found in Vouliagmeni Lagoon. Seasonal qualitative and quantitative samples were extracted from the different types of the substratum during 1997–1998. Overall, 800 individuals of C. glaucum and 2700 individuals of A. ovata were collected and measured and their population structure studied.

The reproductive biology of the tarwhine Rhabdosargus sarba has been studied in three very different environments in Western Australia, namely the lower reaches of the Swan River Estuary and marine waters at the same latitude, i.e. ≈32°S, and a large subtropical marine embayment (Shark Bay) approximately 800 km further north. A macroscopic and histological examination of the gonads demonstrated that R. sarba is typically a rudimentary hermaphrodite in Western Australian waters, i.e. the juveniles develop into either a male or female in which the ovarian and testicular zones of the gonads, respectively, are macroscopically undetectable. This contrasts with the situation in the waters off Hong Kong and South Africa where R. sarba is reported to be a protandrous hermaphrodite. Although R. sarba spawns between mid-late winter and late spring in each water body, the onset of spawning in the estuary is delayed until salinities have risen well above their winter minima. Although males and females attain sexual maturity at very similar lengths in the Swan River Estuary and Shark Bay, i.e. each L50 for first maturity lies between 170 and 177 mm total length (TL), they typically reach maturity at an earlier age in the former environment, i.e. 2 vs 3 years old. During the spawning period, only 25 and 12% of the males and females, respectively, that were caught between 180 and 260 mm TL in nearshore marine waters were mature, whereas 94 and 92% of the males and females, respectively, that were collected in this length-range over reefs, were mature. This indicates that R. sarba tends to move offshore when it has become ‘physiologically’ ready to mature. The L50s at first maturity indicate that the minimum legal length in Western Australia (230 mm TL) is appropriate for managing this species.

The surface-swimming duration of basking sharks (Cetorhinus maximus) was determined in the western English Channel from May to July over a five-year period. Surface duration showed marked variation from 0·17 to 1·45 h over the short time period from late May to mid-June. Stepwise multiple regression was used to identify any relationships between surface-swimming duration and time of day, daily sea surface temperature (SST), and zooplankton density. There was no support for any effects of SST or two measures of zooplankton density (median and maximum densities). However, there were significant relationships for surface duration with time of day and minimum zooplankton density (r2=0·50) indicating basking sharks respond to the abundance of prey and its temporal availability. This suggests that the probability of sighting sharks at the surface will vary depending on the diel period and the surface abundance of zooplankton.