Contrasting feeding patterns among species of fish larvae from the tropical Andaman Sea

Feeding habits of tropical fish larvae were analysed in a comparative study of four species (Scorpaenodes sp., Carangoides sp., Acanthocepola sp. and Cynoglossus sp.) from the Andaman Sea. We investigated morphological characteristics and their potential influence on larval feeding, and looked for common patterns in larval prey preference. Gut contents of a total of 300 larvae were examined and compared with local zooplankton composition. The feeding habits of the investigated larvae shared a number of characteristics. During ontogeny both the preferred prey size and the number of prey in the gut increased, and across all larval size classes the relative prey size spectrum stayed constant, of approximately the same magnitude for all four species. On the other hand, larval feeding also differed in a number of aspects, especially differences in the taxonomic composition of preferred prey were apparent. Scorpaenodes sp. preferred abundant and large prey taxa, Acanthocepola sp. and Carangoides sp. preferred large, but less common prey taxa, while Cynoglossus sp., which had the relatively smallest mouth size, preferred smaller sized prey groups. Hence, the findings indicate that from an offset of common characteristics, especially related to prey size preference, larvae have their individual feeding patterns related to specific morphology and patterns of distribution.Communicated by M. Kühl, Helsingør     

Changes in microflora of a puffer fish Fugu niphobles,with different water temperatures

Grass puffer Fugu niphobles, captured in November 1986 at Shimoda, Japan, and then reared at different temperatures ranging from 10 to 29°C, was examined for microflora changes in the skin, gill and intestines. At 10°C, the skin and gill were colonized mainly by Pseudomonas, Flavobacterium and Moraxella, while at 29°C Vibrio and Flavobacterium appeared abundantly. The intestinal microflora, consisting of Vibrio, Pseudomonas and Flavobacterium, revealed little temperature dependence, although the intrageneric composition of Vibrio changed conspicuously depending on the change of water temperature. Vibrio group 1, tentatively identified as V. alginolyticus, was detected in all tissues examined at 20 and 29°C. This, along with the fact that V. alginolyticus produces tetrodotoxin, suggests that the tetrodotoxin contained in puffer is, at least partly, accounted for by this bacterial species inhabiting intestines.     

Life cycle, seasonal vertical distribution and feeding of Calanus finmarchicus in Skagerrak coastal water

 Day/night zooplankton sampling in Kosterfjorden, Sweden, gave information on population succession, vertical distribution and feeding of Calanus finmarchicus over 17 months. Copepodid Stage 1 and 2 (C-I, C-II) were present from December to August, indicating reproduction during most of the year. Mating and breeding for the overwintering generation mainly took place in February/March, resulting in peak abundance of C-I in March/April. Secondary breeding periods were in April and July/August, but the resulting recruitment from these were low. The relative recruitment success in the first spring was around 13 times higher than during the second spring. Low temperature in the surface water early in the year and depression of the spring phytoplankton bloom may have caused the failure in the second year. Population biomass peaked at >15 g dry weight m⁻² during the numeric peak of the youngest stages in March/April. A more sustainable level of high biomass of 8 to 10 g dw m⁻² was gradually built up during summer, mainly due to a continuous accumulation of C-Vs. Adults and C-Vs comprised the overwintering population, with 7 to 14% and 85 to 93%, respectively, for the 2 years, but only C-Vs staying in the deep water were in a resting state. Adult males showed a strong diurnal vertical migration (DVM) of the usual type from spring to early autumn and a reversed DVM during the cold season. They were in a feeding state throughout the year. Adult females showed the usual type of DVM during summer to autumn, but commonly a reversed DVM during winter to spring. They were usually in a feeding state, with no pronounced differences between surface and deep water or between day and night. C-Vs aggregated in the deep water from October to March and performed DVM in April to June. They were commonly feeding in the deep water between March and June but showed no or very low feeding activity there from July to February. C-Vs in the surface water were commonly feeding and showed the highest proportion of feeding in autumn, when the population in the deep water was inactive. C-V constituted up to nearly 100% of the population biomass, and therefore must be of profound ecological importance. Defined by this dominant role, the population of C. finmarchicus can be characterised as having an active period of feeding, reproduction and development from February to July with a following 6 to 7 months of resting in the deep water, when development is arrested and no feeding occurs. Received: 1 October 1999 / Accepted: 27 April 2000     

Spawning migrations and local movements of a tropical sparid fish

Between June 1994 and September 1996, a mark–recapture study was conducted in the Hinchinbrook Channel area of tropical northeastern Australia to investigate the movements of the sparid fish Acanthopagrus berda. A total of 962 A. berda were tagged, 922 within a single estuary system, Deluge Inlet. No movements among estuaries were detected. Of the fish tagged in Deluge Inlet, 12.9% were recaptured. Two movement regimes were detected: local movements (mostly <500 m) during non-spawning times, and longer migrations (up to 3.12 km) during spawning seasons, to and from a spawning site at the estuary mouth. Although there appeared to be a major spawning aggregation in the mouth of Deluge Inlet, ripe female A. berda were present in upstream sites, indicating that spawning probably occurs there also. This contrasts to the situation in South Africa, where A. berda is reported to spawn only close to estuary mouths. Differences such as this highlight our limited knowledge of variations in the reproductive biology of widespread species such as A. berda. Received: 25 November 1997 / Accepted: 10 September 1998     

Exfoliation of epithelial cells by the scallop Placopecten magellanicus : seasonal variation and the effects of elevated water temperatures

Previous studies have shown that large numbers of ciliated and nonciliated epithelial cells (diam.: 6 to 15 μm) are released by adult sea scallops, Placopecten magellanicus (Gmelin), during summer months in Newfoundland when water temperatures are at a maximum and gonads are well developed. Such exfoliation of cells could be a response to stresses associated with elevated water temperatures and/or spawning activity. In the present study an electronic particle counter/sizer was used to further investigate the factors that influence exfoliation of epithelial cells by juvenile and adult scallops throughout the year. We observed release of epithelial cells from juveniles, and from adults collected in months when gametogenic activity was minimal, indicating that exfoliation does not occur as a result of reproductive activity alone. SEM analysis revealed little difference in surface characteristics of the gills, mantle and gonad between scallops that had released cells and those that had not, suggesting that exfoliation of small numbers of cells may be a consequence of cellular turnover and normal physiological function. Adult scallops were monitored in a second experiment to determine the effects of raising water temperatures from 8.5 to 14.7 and to 21.0 °C on the frequency (proportion) and rate of cellular exfoliation. Only at the highest experimental temperature (21.0 °C) were exfoliation rates significantly higher than rates recorded at 8.5 or 14.7 °C. SEM analyses revealed some damage to gill, mantle and gonad tissues when scallops were exposed to 14.7 and then to 21.0 °C for a total of 8 d. Received: 21 August 1996 / Accepted: 13 September 1996     

Yolk resorption,onset of feeding and survival potential of larvae of three tropical marine fish species reared in the hatchery

This paper provides basic early life-history information on milkfish (Chanos chanos), seabass (Lates calcarifer) and rabbitfish (Siganus guttatus) which may explain in part the observed differences in their survival performance in the hatchery. Egg size, larval size, amount of yolk and oil reserves and mouth size are all greater in milkfish than in seabass, and greater in the latter than in rabbitfish. During the first 24 h after hatching, rabbitfish larvae grow much faster than milkfish and seabass larvae at similar ambient temperatures (range 26°–30°C, mean about 28°C). The eyes become fully pigmented and the mouths open earlier in seabass and rabbitfish (32–36 h from hatching) than in milkfish (54 h). Seabass larvae learn to feed the earliest. Yolk is completely resorbed at 120 h from hatching in milkfish, and yolk plus oil at 120 h in seabass and 72 h in rabbitfish at 26° to 30°C. Milkfish and seabass larvae have more time than rabbitfish to initiate external feeding before the endogenous reserves are completely resorbed. Delayed feeding experiments showed that 50% of unfed milkfish larvae die at 78 h and all die at 150 h from hatching. Milkfish larvae fed within 54 to 78 h after hatching had improved survival times: 50% mortality occurred at 96 to 120 h, and 10 to 13% survived beyond 150 h. Unfed seabass larvae all died at 144 h, while 6 to 13% of those fed within 32 to 56 h after hatching survived beyond 144 h and well into the subsequent weeks. Unfed rabbitfish larvae all died at 88 h, while 7 to 12% of those fed within 32 to 56 h after hatching survived beyond 88 h. A delay in initial feeding of more than 24 h after eye pigmentation and opening of the mouth may be fatal for all three species.Contribution No. 167 from the SEAFDEC Aquaculture Department     

Tolerance to high temperatures and potential impact of sea warming on reef fishes of Gorgona Island (tropical eastern Pacific)

Knowledge of upper thermal-tolerance limits of marine organisms in the tropical eastern Pacific (TEP) is important because of the influence of phenomena such as El Niño and global warming, which increase sea temperature. Laboratory experiments were conducted to determine the critical thermal maximum (CTM) of reef fishes from the TEP. In 15 reef fishes of Gorgona Island (TEP) the CTM was between 34.7°C and 40.8°C. None of these CTMs was exceeded by sea temperature in the TEP during any of the strongest El Niño events in this century (32°C during El Niño 1982-1983 and 1997-1998), which indicates that all species studied here may tolerate El Niño maximum temperatures. In addition, the CTM of the least-tolerant species was 8°C above the current mean sea temperature in a wide range of latitudes in the TEP. This suggests that fishes live far from their upper thermal tolerance limits and that the current global-warming trend is still unlikely to be dangerous for these species. If sea temperature continues to increase at the current rate, in about a century sea temperature could exceed the thermal tolerance of some reef fishes and threaten them with extinction. Such risk, however, might occur sooner if the sea temperature during El Niño also increased in step with the global warming, but also because other processes involved in maintaining population, such as reproduction, can be affected at lower temperatures. The possible ability of reef fishes to adapt to increases in sea temperature is discussed.     

Association of color and feeding deterrence by tropical reef fishes

Summary. While many marine molluscs have been suggested to use aposematic coloration to avoid predation, few studies have tested the ability of marine predators to learn to associate colors with distasteful prey. In field experiments, we tested the ability of two populations of reef fishes to discriminate among red, yellow, and black artificial nudibranch models when one color was paired with a feeding deterrent. We offered fishes (1) the models without any feeding deterrents, (2) the models with a feeding deterrent coated onto one color, and (3) the models without deterrents again. If reef fishes learn to associate colors with noxious prey, we expected the color paired with the feeding deterrent to be eaten less frequently in the final assay than the initial assay. In both populations, fishes formed clear associations between color and feeding deterrence. However, when the experiment was repeated in one population, changing the color paired with the feeding deterrent, fishes did not form an association between color and feeding deterrence. In this case, prior learning may have affected subsequent trials. Our study indicates that common colors of nudibranchs are recognizable by fishes and can be associated with noxious prey. Received 24 September 1998; accepted 18 December 1998.     

Reproductive cycle and seasonal feeding activity of the neogastropod Buccinum undatum

The whelk Buccinum undatum L. in the northern Gulf of St. Lawrence has a distinct annual reproductive cycle. The ovary and pallial oviduct of the female, and the seminal vesicle of the male, show parallel development, whereas the testis has an inverse cycle. Thus, at the end of winter when the ovary, pallial oviduct and seminal vesicle reach maximal size, the testis is small and undeveloped, whereas the reverse situation occurs in summer. This is the first report of a totally inverse relationship between the ovary and testis for a marine invertebrate. This unusual pattern is due to the long-term storage of sperm in the seminal vesicle of the male prior to copulation. There is no resting period at the end of oogenesis, but rather renewed ovarian development starts shortly after gamete release. By contrast, in the testis after transfer of sperm to the seminal vesicle at the end of spermatogenesis, there is a distinct period of phagocytosis. Mating begins in mid-May, reaches a peak during June and terminates prior to July. Egg laying begins in late May, reaches a peak in mid-June to mid-July and can continue until late August. Examination of the incidence of individuals with food in their stomachs showed that feeding activity is maximal in late autumn through to early spring and decreases sharply coincident with the onset of breeding in late May.     

Control of populations of the coral-feeding nudibranch Phestilla sibogae by fish and crustacean predators

Juvenile lesser blue crabs, Callinectes similis Williams, were exposed to a range of salinities for measurement of survival and bioenergetics. Effects of salinity on survival were determined by exposing juvenile crabs to salinity treatments ranging from 0 to 74‰. All crabs survived 21 d of exposure to 5 and 45‰S. The 21 d LC₅₀ values for salinity tolerance (calculated from survival data) were 2.6 and 60.8‰S at low and high salinities, respectively. Energy-budget components and scope for growth were determined for crabs exposed to 2.5, 10, 25, 35 and 50‰S. Energetic absorption rates were highest at 2.5 and 35‰S. Energetic expenditure rates (energy lost to respiration and excretion) were greatest at 2.5‰S, and decreased as salinity increased. Respiration constituted the majority of energetic expenditure at all salinities (92.3% average). Scope for growth was significantly affected by salinity and was highest in crabs exposed to 35‰S. Increased respiration at low salinity may indicate that C. similis incurs greater costs due to osmoregulation. The results of this study indicate that C. similis is capable of surviving and growing in waters with salinities as low as 10‰. Received: 10 January 1997 / Accepted: 11 February 1997     

Diel and seasonal changes in the distribution of fish on a southeast Brazil sandy beach

The effect of diel and seasonal changes in the distribution of fishes on a subtropical sandy beach on the southeastern coast of Brazil were studied. Seine netting was carried out on both seasonal and diel scales between July 1998 and June 1999. A total of 46 fish species was recorded, six being numerically dominant: Anchoa tricolor, Gerres aprion, Harengula clupeola, Atherinella brasiliensis, Mugil liza and Diapterus rhombeus. Seasonal changes in abundance of dominant species were detected. Species dominant in winter were Anchoa tricolor, H. clupeola and Atherinella brasiliensis; in spring, Anchoa tricolor and G. aprion; in summer G. aprion and D. rhombeus; and in autumn M. liza and H. clupeola. Overall, diel patterns did not reveal any significant trends; however, if we consider each season separately, an increase in A. tricolor abundance was recorded during the day in winter/spring, being replaced at night by H. clupeola in winter, and by G. aprion in spring. Increases in number of individuals and biomass at sunset, and decreases during the night were recorded. The winter/spring inshore/offshore movements at diel scale performed by the three most abundant species demonstrate that diel fluctuation acts more at a species-specific level than at a structural one; in summer there was no evidence of diel movements due to a heavy influx of G. aprion and D. rhombeus, which use the area throughout day and night, increasing overall abundance. Seasonal movements seems to be related to ontogenetic change in species, while diel movements in the fish assemblage seem to be more related to physiological requirements, such feeding activity of each particular species, than to physico-chemical conditions.Communicated by O. Kinne, Oldendorf/Luhe     

Cephalopod hatchling growth: the effects of initial size and seasonal temperatures

Temperature is known to have a strong influence on cephalopod growth during the early exponential growth phase. Most captive growth studies have used constant temperature regimes and assumed that populations are composed of identically sized individuals at hatching, overlooking the effects of seasonal temperature variation and individual hatchling size heterogeneity. This study investigated the relative roles of initial hatchling size and simulated natural seasonal temperature regimes on the growth of 64 captive Octopus pallidus over a 4-month period. Initial weights were recorded, and daily food consumption and fortnightly growth monitored. Two temperature treatments were applied replicating local seasonal water temperatures: spring/summer (14–18°C) and summer/autumn (18–14°C). Overall octopuses in the spring/summer treatment grew at a rate of 1.42% bwd⁻¹ (% body weight per day) compared to 1.72% bwd⁻¹ in the summer/autumn treatment. Initial size influenced growth rate in the summer/autumn treatment with smaller octopuses (<0.25 g) growing faster at 1.82% bwd⁻¹ compared to larger octopuses at 1.68% bwd⁻¹. This was opposite to individuals in the spring/summer treatment where smaller octopuses grew slower at 1.29% bwd⁻¹ compared to larger octopuses at 1.60% bwd⁻¹. Initial size influenced subsequent growth, however, this was dependent on feeding rate and appears to be secondary to the effects of temperature.     

Heavy metals in water of the rivers Hooghly and Haldi at Haldia and their impact on fish

The paper deals with the measurement of five heavy metals viz., Cd, Cu, Mn, Pb and Zn in water of the rivers Hooghly and Haldi at Haldia during June 1999 to October 2002. The industrial effluent out fall (OF) at Patikhali, Haldia was also taken as sampling site along with above out fall (AOF) and below out fall (BOF) sites. Most of the metals exhibited their least concentration at the sampling site above the Haldia industrial area of river Hooghly. The average concentrations of the studied metals were Cd 2-14, Cu 5-19, Mn 8-88, Pb 17-41 and Zn 22-37 microg l(-1). Comparison of the data with the Criterion Continuous Concentration (CCC) of USA revealed that Cd, Cu and Pb were the pollutants present at alarming level to disturb the aquatic life process in the zone. The effect was found to reflect on the tissue level aberrations in the residential fishes. The other two metals viz., Mn and Zn were probably less harmful to the aquatic ecosystem. In India, necessity is felt to develop the CCC values, which will be more appropriate for protection of aquatic environment than comparing with drinking water standards.     

Spatial and seasonal differences in the fish fauna in the shallows of a large Australian estuary

Samples of fish were collected by beach seine throughout the shallow waters of the large Peel-Harvey estuarine system (south-western Australia) in the wet (June to November) and dry periods (December to May) between August 1979 and July 1981. The number of species, density and biomass declined with distance from the estuary mouth and rose with increasing temperature and salinity. Both classification and ordination distinguished the faunal composition of the saline reaches of the rivers from that of the narrow Entrance Channel and two large basins (Peel Inlet and Harvey Estuary). Classification also separated the fauna of the riverine group into wet- and dry-period components, and divided samples taken in the Entrance Channel from those in the basins. Differences between the faunal composition of the Peel Inlet and its tributary rivers were related to differences in salinity regime. The riverine fauna was subjected to much more variable and lower minimum salinities. Species characteristic of the rivers included teleosts such as Atherinosoma wallacei and Amniataba caudavittatus, which are estuarine sensu stricto in southwestern Australia, the semi-anadromous Nematalosa vlaminghi and juveniles of the marine Mugil cephalus. The species diagnostic of the wet periods in the rivers were the estuarine species A. wallacei and Favonigobius suppositus, while the dry periods were characterised by the marine species Atherinomorus ogilbyi and Sillago schomburgkii. Marine species also characterised the Entrance Channel (Favonigobius lateralis, Sillago bassensis), whereas the indicators in Peel Inlet and Harvey Estuary were Hyporhamphus regularis and Apogon rueppellii, both of which can pass through the whole of their life cycle in estuarine as well as marine environments.     

Home range, activity and distribution patterns of a temperate rocky-reef fish, Cheilodactylus fuscus

Red morwong (Cheilodactylus fuscus; Cheilodactylidae: Perciformes), are large temperate rocky reef fish that are patchily distributed in local aggregations of 3 to >100 fish. The home ranges and aggregating behaviour of red morwong were investigated using external tags (n = 114, over 35 mo) and ultrasonic transmitters (n = 9 over 20 d) at coastal and estuarine sites in south-east Australia. Adult red morwong had a mean home range during the day of 1865 m² (SE = 268). Night movement, determined by ultrasonic telemetry, indicated a significantly greater mean home range of 3639 m² (SE = 416). Home range did not differ significantly with size or sex. Fish movements were greatest and aggregation sizes varied most during the non-reproductive mid-summer period. Tagged fish (N = 20) displaced 200 to 900 m returned in 1 to 3 d to the point of capture, often traversing open sand habitat and other aggregations. During the day, fish were commonly found on bouldered habitat. During the night, these site-specific aggregations fragmented as fish dispersed over a variety of substrata, with crepuscular peaks in activity. Therefore, estimates of habitat-specificity and feeding patterns collected only by day may give misleading results. Received: 28 June 1996 / Accepted: 8 July 1998     

Comparison of fine-scale acoustic monitoring systems using home range size of a demersal fish

We compared the results from fixed acoustic transmitters and transmitters implanted in lingcod Ophiodon elongatus provided by two fine-scale passive acoustic monitoring systems: the older Vemco^? Radio Acoustic Positioning (VRAP) system and the newer VR2W Positioning System (VPS) with either three or four receivers. The four-receiver VPS method calculated five times more positions of lingcod than VRAP and more than twice as many as the three-receiver VPS. Calculated positions of fixed transmitters were less precise with VRAP than either VPS approach. Measurements of home range for lingcod were similar between the four-receiver VPS and VRAP, which were both greater than the three-receiver VPS. Comparisons varied when lingcod were in/near complex habitats. As new technology develops, it is important to understand how new methods compare to previous methods. This may be important when describing patterns of movement or habitat use in the context of changes in habitat or management efforts.     

Effects of feeding history on the growth characteristics of a reef fish at settlement

A feeding experiment was conducted on the pelagic stages of the tropical goatfish Upeneus tragula (family Mullidae) to examine how food quantity affects growth characteristics and potential success at settlement. Pelagic goatfish were collected from aggregation rafts 3 nautical miles west of Lizard Island on the northern Great Barrier Reef during December 1990. Three tanks in each of four feeding regimes were stocked with 25 pelagic goatfish between 20 and 23 mm standard length (SL). The four feeding regimes were: fed ad lib. (fed): fed once per day (f1pd); starved every second day (stld); starved for 3 d and re-fed (st3d). Fishes were fed 36 to 48 h old Artemia sp. nauplii (Ocean Star strain). Fish were removed from tanks when they underwent metamorphosis, changed pigmentation and settled to the bottom of the tanks. Morphology, muscle development, time taken to settle and biochemical condition were examined. Growth attributes of the treated fish were compared to fish which settled within 24 h of capture (field). All attributes examined were significantly influenced by the feeding treatments. Fish within the fed and st3d treatments were significantly larger and heavier than fish in the less well-fed treatments (f1pd, st1d). Similarly, concentrations of total lipid, carbohydrate and protein in the settled fish were significantly higher in the fed and st3d treatments compared with the st1d and f1pd treatments. For all these morphological and biochemical attributes the st1d and f1pd fish did not significantly differ from the field fishes, but did differ from the fed and st3d fishes. Water content was significantly higher in the f1pd, st1d and field fishes compared with the fed and st3d fish. Furthermore, the average time taken to settle followed the pattern: fed (14d)U. tragula are physiologically well suited to exploiting a patchy food source, and that food availability within the pelagic stages can have a major influence on the growth characteristics of this reef fish at settlement. The ramifications of this finding are discussed in relation to survival and success once fish have recruited to the reef population.     

Understanding determinants of home range behaviour of feral cats as introduced apex predators in insular ecosystems: a spatial approach

The introduced feral cat (Felis catus) is a widespread generalist with flexible social behaviour and an apex predator without major interspecific competitors in insular ecosystems that evolved in the absence of predators. Mechanistic definitions consider an animal’s home range to be the spatial expression of a cognitive map that is kept up-to-date with the status of critical resources that contribute to animal fitness. We assumed there are two major determinants structuring the home range of cats as apex predators in insular ecosystems: the distribution of critical food resources and conspecific distribution. We hypothesized that cats structure their home ranges by optimizing the use of staple critical food resources and that as a consequence of the presence of rich resources cats tend to socialise, aggregate and share space. We carried out spatial analyses using location data for feral cats tracked using lightweight GPS collars in conjunction with the suitability value of rabbit patches and their associated ownership costs for cats within a New Zealand braided-river environment. Cat home ranges and spatial distribution, especially for females, were related to the inclusion of rabbit patches within home ranges with higher mean value than the average of neighbourhood patches in the landscape. Cats showed solitary behaviour but tolerance to conspecific presence by sharing high-use areas and high-value rabbit patches, mostly at different times, resulting in occasional encounters among males and females. Home range size and patterns of spatial overlap were dependant on sex and season. Solitary spacing patterns as consequence of innate preferences together with resource constraints may regulate feral cat population densities.