Rhythms in larval release of the sublittoral crab Neopanope sayi and the supralittoral crab Sesarma cinereum (Decapoda: Brachyura)

Ovigerous females of the subtidal xanthid crab Neopanope sayi (Smith) and the high intertidal grapsid crab Sesarma cinereum (Bosc) were collected during the summers of 1986 and 1987 in the Beaufort, North Carolina (USA), area and brought into the laboratory, where rhythms in larval release were monitored. When crabs with late-stage embryos were put under a 14 h light:10 h dark cycle in an otherwise constant-environment room, an apparent tidal rhythm in release of larvae was observed for both species, with N. sayi releasing near the time of day and night high tides, and S. cinereum releasing around the time of night high tides. The time of sunset relative to high tide was a complicating factor, since larval release for both species was often concentrated around sunset when evening high tides fell several hours before sunset. When a group of N. sayi and S. cinereum were brought into the laboratory and placed under constant lowlevel light for 5 d, the release rhythm of the population persisted, thus implying that the rhythm is endogenous. Larval release near the time of high tide and often at night is common among brachyurans living in tidal areas, regardless of specific adult habitat, suggesting a common functional advantage. Possibilities include transport of larvae from areas where predation and the likelihood of stranding and exposure to low-salinity waters are high, as well as a reduced probability of predation on adult females. Results of the present study suggest that the importance of release after darkness may increase with increasing tidal height of the adult.     

Hatching rhythms in Uca pugilator (Decapoda:Brachyura)

Gravid female Uca pugilator (Bosc) maintained in conditions of 14h L: 10h D light regime and constant temperature without simulated tides showed a significant positive correlation between time of hatch and time of the nighttime high tide. Light: Dark experiments showed no entrainment by LD cues. Larval hatching was delayed until dark when high tide occurred between 1900 and 2130 hrs. Hatch time was a positive linear function of the time of the nighttime high tide when high tide occurred after 2130 hrs. Time of hatch was delayed by the light period on days lacking a nighttime high tide. Experiments conducted under constant light (LL) and temperature, without simulated tides, indicated a persistent free-running rhythm of approximately 25 h 03 min, suggesting an endogenous timer. Rhythmic larval release on the nighttime high tide may be adaptive as a predator-avoidance mechanism for adult gravid females.Contribution No. 366 from the Belle W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina     

Circatidal swimming behavior of brachyuran crab zoea larvae: implications for ebb-tide transport

Larvae of the blue crab Callinectes sapidus and fiddler crab Uca pugilator are exported from estuaries and develop on the continental shelf. Previous studies have shown that the zoea-1 larvae of some crab species use selective tidal-stream transport (STST) to migrate from estuaries to coastal areas. The STST behavior of newly hatched larvae is characterized by upward vertical migration during ebb tide followed by a descent toward the bottom during flood. The objectives of the study were (1) to determine if newly hatched zoeae of U. pugilator and C. sapidus possess endogenous tidal rhythms in vertical migration that could underlie STST, (2) to determine if the rhythms persist in the absence of estuarine chemical cues, and (3) to characterize the photoresponses of zoeae to assess the impact of light on swimming behavior and vertical distribution. Ovigerous crabs with late-stage embryos were collected from June to August 2002 and maintained under constant laboratory conditions. Following hatching, swimming activity of zoeae was monitored in darkness for 72 h. U. pugilator zoeae displayed a circatidal rhythm in swimming with peaks in activity occurring near the expected times of ebb currents in the field. Conversely, C. sapidus zoeae exhibited no clear rhythmic migration patterns. When placed in a light field that simulated the underwater angular light distribution, C. sapidus larvae displayed a weak positive phototaxis at the highest light levels tested, while U. pugilator zoeae were unresponsive. Swimming behaviors and photoresponses of both species were not significantly influenced by the presence of chemical cues associated with offshore or estuarine water. These results are consistent with predictions based on species-specific differences in spawning and the proximity of hatching areas to the mouths of estuaries. U. pugilator larvae are released within estuaries near the adult habitat. Thus, ebb-phased STST behavior by zoeae is adaptive since it enhances export. Selective pressures for a tidal migration in C. sapidus larvae are likely weaker than for U. pugilator since ovigerous females migrate seaward prior to spawning and hatching occurs near inlets and in coastal waters.     

Distribution,habitat preferences and breeding periods in the crustaceans Sesarma cinereum and S. reticulatum (Brachyura: Decapoda: Grapsidae)

The distribution and habitat preferences of Sesarma cinereum and S. reticulatum were studied in the region of Beaufort, North Carolina, USA. S. cinereum inhabits the supralittoral zones of marshes characterized by high salinities (mean=27.9%) and sandy substrates, while s. reticulatum were found to prefer eulittoral marshes with brackish salinities (mean=16.2%) and silty substrates. Major differences have also been found in the cycling of egg production between these two species. Populations of S. cinereum produce approximately 4 to 6 egg batches in close synchrony with the lunar phase, whereas populations of S. reticulatum produce only from 2 to 3 batches of young per breeding season. It appears that female S. cinereum invest less time in carrying their eggs (approximately 1 lunar month), while female S. reticulartum invest a greater amount of time (eggs carried for approximately 45 days). These and other specific differences in reproductive strategies suggest that populations of S. cinereum are responding to density-independent selective pressures, while populations of S. reticulatum exhibit characteristics of density-dependent selective effects.     

Control of larval release in the Caribbean spiny lobster, <Emphasis Type="Italic">Panulirus argus</Emphasis>: role of chemical cues

The current model for larval release in subtidal crustaceans suggests that hatching time is controlled by the embryos, which release a pheromone that stimulates the parent female to undergo behaviors that synchronize larval release. Alternatively, hatching could be controlled by the females. Ovigerous spiny lobsters Panulirus argus (Latreille) exhibit stereotypic behaviors during larval release, including rapid abdominal extensions and pleopod-pumping activity. Ovigerous P. argus were collected from coral reefs in the Florida Keys, USA during the summers of 2005 and 2006. Pleopod-pumping activity was quantified to determine if a female’s pumping activity correlates with the developmental state of the embryos. The role of pheromones released by developing and hatching embryos in controlling pumping behaviors was tested by measuring the pumping response of ovigerous lobsters to (1) hatch water, (2) homogenized embryo water, (3) embryo-conditioned water (unhatched late-stage embryos soaked for 20 h), and (4) water containing homogenized post-hatch embryo cases. Bioassays were conducted under constant conditions (dim-red light) in the laboratory at random times during the day to control for any possible rhythm in pumping activity. Spontaneous pleopod-pumping activity increased significantly with increasing embryo development. Upon exposure to hatch water, ovigerous lobsters with late-stage embryos displayed increased pleopod pumping with increased treatment concentration. Water individually conditioned with homogenized late-stage embryos, intact late-stage embryos, and homogenized post-hatch embryo cases all induced larval release behaviors in females with late-stage embryos. Ovigerous females with early-stage embryos did not respond to water conditioned with homogenized early- or late-stage embryos. These results suggest that active substances are released by embryos at the time of hatching and induce the stereotypical pumping behaviors of the female that synchronizes larval release. The results support the model that larval release in subtidal crustaceans is controlled by pheromones released from hatching embryos.     

Larval biology of six species of the genus Conus (Gastropoda: Toxoglossa) in Hawaii,USA

Among the Hawaiian species in the genus Conus, larval life histories range from long-term planktotrophy to nonpelagic lecithotrophy. Prehatching developmental time, hatching size, pelagic period and total prejuvenile developmental time are all significantly correlated with egg size, while settling size is correlated with none of these larval characteristics. Therefore, larval life history patterns in the genus Conus appear to be determined by 2 sets of selective forces: the first influencing egg size, and the second stipulating settling size. As egg sizes become larger, hatching sizes and prehatching developmental time increase while pelagic periods and total prejuvenile developmental times decrease. Settling size appears to be related to water depth, but food requirements of newly metamorphosed juveniles may also be important.     

Reproductive,growth and life-history contrasts between two species of grapsid crabs,Sesarma cinereum and S. reticulatum

Two grapsid crabs, Sesarma cinereum (Bosc) and S. reticulatum (Say), were studied in the region of Beaufort, North Carolina, USA, during the summers of 1977, 1983, and 1984. The two grapsid species showed differences in social organization, habitat preferences, and number and size of first-stage larvae. We analyzed several other characters (growth rates, size at sexual maturity, reproductive effort per clutch) to determine if these differences could be related to a coherent pattern of life-history trends. While some relationships between characters were consistent with those found among other crab species, few seemed peculiarly matched to the ecological contrasts represented by our species. Our results suggest that other factors (phyletic predisposition; decoupling of selection between larval and adult stages; equally adaptive alternatives) may obscure the rules governing relationships between life-history characters and evolutionary trends.     

Recruitment to adult habitats following marine planktonic development in the fiddler crabs, Uca pugilator, U. pugnax, and U. minax

Three congeneric species of fiddler crabs, Uca pugilator (Bosc, 1802), U. pugnax (Smith, 1870), and U. minax (LeConte, 1855), co-occur in estuaries along the east coast of North America, from Cape Cod to northern Florida. Although U. minax adults are generally found at lower salinities than the other two species, the distributions of all three species overlap to some degree. The distribution of megalopae and juvenile fiddler crabs (from first crab stage to those with a carapace width of 3.0 mm) was examined at four sites along a salinity gradient (from 35.0±2.0 to 3.0±3.0; ) in the North Inlet Estuary, South Carolina, USA, in August 2002. A PCR-RFLP technique was developed to identify individuals from the genus Uca to species from first zoea through the early crab stages. An examination of the distribution of early life stages showed that U. minax reinvades low-salinity adult habitats at settlement, following planktonic larval development in the coastal ocean. Also, juveniles of U. pugilator were found to occupy Spartina alterniflora stands, where adult conspecifics rarely occur. Species frequencies were different for adults compared to early life stages in low-salinity areas of the marsh, where populations overlap. Settlement and survival dynamics of early life-history stages in wet and dry years likely determine the distribution of adult Uca spp. populations along salinity gradients in estuarine ecosystems.Communicated by J.P. Grassle, New Brunswick     

Cloning and expression of high choriolytic enzyme,a component of the hatching enzyme system,during embryonic development of the marine ornamental fish<Emphasis Type="Italic"> Chrysiptera parasema</Emphasis>

In the present study, a cDNA for the hatching enzyme of a marine tropical fish, Chysiptera parasema, was cloned. This is the first demonstration of hatching enzyme cDNA from a marine tropical fish. The amino acid (aa) sequence deduced from the cDNA consisted of an 18-aa signal sequence, a 53-aa propeptide sequence and a 196-aa mature enzyme portion, having a consensus active site sequence for astacin family proteases. Phylogenetic analysis showed that the C. parasema enzyme was included in the clade of HCEs (high choriolytic enzymes), one of the hatching enzymes of freshwater fishes such as medaka (Oryzias latipes), masu salmon (Oncorhynchus masou) and zebrafish (Danio rerio), but not in the group of LCEs (low choriolytic enzymes), another type of hatching enzymes identified in the medaka. The developmental expression patterns of the C. parasema HCE gene were highly similar to that of the medaka HCE gene. The results suggested that the hatching enzyme system is highly conserved between these marine and freshwater fish species.Communicated by R. Cattaneo-Vietti, Genova     

Effects of embryonic exposure to conspecific chemical cues on hatching and larval traits in the common frog <Emphasis Type="Italic">(Rana temporaria)</Emphasis>

Summary. Recent studies indicate that amphibian eggs are capable of hatching plasticity in response to chemical cues released by predators feeding on conspecific eggs or larvae. However, information is scarce on the relative importance of predator and conspecific cues in such a process. In particular, no attempt has been made to compare the effects of embryonic exposures to chemical cues indicative of a predation risk for eggs and larvae, although both life stages can co-occur in natural habitats. In this context, common frog embryos (Rana temporaria) were raised until hatching in the presence of crushed conspecific extracts from eggs and tadpoles to assess their respective influences on some hatching and larval traits. While a significant delay in hatching time was observed in embryos exposed to chemical cues from tadpole extract, this life-history shift appeared unaffected by embryonic exposure to egg extract. Hatchlings derived from eggs incubated in the presence of both conspecific extracts showed a significantly greater weight than unexposed controls. However, such an effect was no longer apparent 15, 30 and 50 days after hatching, suggesting that embryonic exposure to chemical cues from damaged conspecific eggs and tadpoles has no influence on larval growth. Lastly, morphological measurements performed on hatchlings and older tadpoles (15, 30 and 50 days old) revealed no significant effect of embryonic treatments on the shape of body and tail.     

Fecundity,brood loss and egg development through embryogenesis of <Emphasis Type="Italic">Armases cinereum</Emphasis> (Decapoda: Grapsidae)

The present work is a comprehensive study of reproduction and embryonic development of Armases cinereum. Ovigerous A. cinereum (Bosc, 1802) females from Sebastian Inlet, Florida (9.88–19.4 mm CW) lay 2,000–12,000 eggs per brood, depending on their CW (mm): fecundity = 24.662 CW^1.9432. A. cinereum displayed significant brood loss through development (ca. 500 eggs per brood) independently from their CW (no senescence). However, since smaller females lay fewer eggs than larger ones, the percentage of eggs lost during embryonic development is greater in smaller females. The number of eggs carried on a later stage of development (potential fertility = 5.5593 CW^2.4417) is a more accurate estimate of the reproductive output and subsequent recruitment. Egg volume increased during development (64%, 0.025–0.041 mm³ or 0.36–0.43 mm of diameter, N = 270) and was strongly correlated with egg water content increase (19.21%, r = 0.89). Lipids, particularly fatty acids, seem to be the major energy source for embryonic development, decreasing 56.31 and 37.08% (respectively) during embryonic development; both are negatively correlated with egg volume (r = −0.90). The utilization of fatty acids through the different developmental stages of A. cinereum is presented. The most consumed fatty acids are the monounsatured (43.33 μg mg⁻¹ dw), followed by the saturated (29.91 μg mg⁻¹ dw) and polyunsaturated (24.03 μg mg⁻¹). Palmitic (16:0) and linoleic (18:2n-6) acids are preferentially consumed (19.5 and 17.9 μg mg⁻¹ dw, respectively). The high proportion of essential polyunsaturated fatty acids of C₁₈ and C₂₀ reflects the consumption of primary producers such as mangrove leaves. EPA/DHA ratio (2.85–3.84) and low DHA content indicated that this species appears in a medium-low level of the trophic chain. The low ratio of 18:1n-7/18:1n-9 and high percentage of 18:1n-9 (marker of carnivory) may be a sign of the consumption of juvenile invertebrates. The high percentage of odd-numbered FA indicated the occurrence of detritivores/scavenger behaviours. The fatty acid composition of the eggs reflects adult feeding ecology (omnivorous) and habitat.     

Salinity favorable for early development and gamete compatibility in two sympatric estuarine species of the genus Hediste (Polychaeta: Nereididae) in the Ariake Sea, Japan

Early development was examined, under various salinities, for two sympatric nereidid polychaetes, Hediste japonica and H. diadroma, which participated in a simultaneous reproductive swarming in an estuary of the Omuta-gawa River in Ariake Sea, Japan. The eggs of both species were isotonic to the medium of 27.5–30 psu salinity. The egg diameter in the isotonic salinity was 180–205 μm in H. japonica, and 130–160 μm in H. diadroma. Successful development of most embryos was observed in a salinity range of 22.5–30 psu in both species, while successful fertilization occurred in wider ranges of salinity, i.e., 10–34 psu in H. japonica and 10 to 30 psu in H. diadroma. In both species, free-swimming larval life started from the indistinct hatching of trochophores out of a jelly layer capsule. The lecithotrophic development appeared to run to the 4-setiger nectochaetes in H. japonica, while to 3-setiger nectochaetes in H. diadroma, resulting in a shorter pelagic larval life in H. japonica. In a comparison of larval morphology among Hediste species, we found a definite negative correlation between the prostomium width, which represents the larval size and depends on egg size, and relative length of chaetae to the prostomium width: the relative length of chaetae was the longest in H. diadroma (with the smallest egg size and long pelagic life), intermediate in H. japonica (intermediate egg size, short pelagic life), and the shortest in H. atoka (largest egg size, no true pelagic life). We also examined the possibility of hybridization between H. japonica and H. diadroma through cross-insemination experiments. The gametes of the two species were reciprocally compatible, and viable hybrid offspring were produced by the laboratory crosses. The hybrid larvae expressed intermediate phenotypes, but with a greater maternal influence in characteristics such as the relative length of chaetae and the lecithotrophic larval duration.     

Comparative fertilization biology of gymnolaemate bryozoans

Locations and oogenic stages of eggs at the time of sperm-egg fusion were determined for nine gymnolaemate species exhibiting different reproductive strategies with respect to site of embryonic development (e.g., water column, introvert, embryo sac, or ovicell) larval type, and zooid sexuality. Ovarian, coelomic, and recently spawned oocytes obtained from freshly collected colonies between 1988 and 1995 were stained with aceto-orcein and examined for the presence of a sperm nucleus. All nine species are shown to have a similar fertilization biology in which sperm fuse with eggs in or near ovaries and egg activation is delayed until eggs are spawned. In species such as the etenostomeAlcyonidium sp. and the cheilostomeElectra pilosa (Linnaeus, 1767), which produce marierons oocytes that are spawned into the water column and have cyphonautes larvae, sperm fuse with late growth stage ovarian oocytes after germinal vesicle breakdown (GVBD) at or near ovulation. In species that produce few oocytes, brood embryos, and release coronate larvae, sperm fuse with late growth stage ovarian primary oocytes before GVBD, as in the ctenostomeBowerbankia gracilis Leidy, 1855, or with very early growth stage ovarian primary oocytes, as in the cheilostomesCribrilina corbicula (O'Donoghue, 1923),Dendrobeania lichenoides (Robertson, 1900),Hippodiplosia insculpta (Hincks, 1882),Schizoporella serialis (Heller, 1867),T ricellaria gracilis (Smitt, 1867), andWatersipora arcuata Banta, 1969. Fertilization success was high in all nine species, with 83 to 100% of oocytes at an appropriate oogenic stage containing a sperm nucleus or early male pronucleus. Gymnolaemate bryozoans may maintain high levels of fertilization success by: (1) concentrating spawned sperm from the water column using colony feeding currents; (2) localizing sperm-egg encounters in or near the ovary, (3) using sperm when available by permitting sperm to fuse with early growth stage oocytes; and (4) selfing.     

Extracellular organic carbon (EOC) in the genusCarpophyllum (Phaeophyceae): Diel release patterns and EOC lability

Release of extracellular organic carbon (EOC) by the four species of the brown alga genusCarpophyllum was investigated in light : dark incubations of 30 to 40 h duration using a¹⁴C-method. Plants were collected during 1986 in the Hauraki Gulf area, Auckland, New Zealand. InC. maschalocarpum (Turn.) Grev. andC. plumosum (A. Richard) J. Ag. rather low release rates in light (2 to 5% of the photosynthetic rates) were followed by high release rates after 4 to 5 h in darkness (10 to 15% of previous photosynthetic rates). The opposite pattern, with high release in light and low in darkness, was found in experiments withC. angustifolium J. Ag. andC. flexuosum (Esper) Grev. The pattern with substantially higher release in dark than in light is observed for the first time. EOC products were dominated by small molecules (<1000 daltons) in all four species and both in light and darkness. Decomposition experiments exhibited a preferential bacterial utilization of low molecular weight products. Thus, a relative enrichment with larger molecules took place. Bacterial conversion efficiencies of EOC in 5-d experiments averaged 0.24 and 0.09 for products released in light and dark, respectively. The rate constants for decomposition of products released in light were lower than for those released in darkness.     

Egg release and settlement patterns of dioecious and hermaphroditic fucoid algae during the tidal cycle

The timing of gamete release by fucoid algae, although known to be restricted to calm days is not clearly understood within a circadian time scale. The need for externally fertilizing species to avoid gamete dilution suggests that in wave-exposed areas spawning may occur during particular tidal phases. However, this may differ between mating systems, as selfing species may be less affected by gamete dilution. In this study, two different approaches were used to determine when egg release occurs during the tidal cycle in two sister species with different mating systems. First, egg settlement of Fucus vesiculosus (dioecious) and Fucus spiralis (selfing hermaphrodite) was quantified on removable substrates (egg settlement disks) every day for 2 months and settlement patterns were used to statistically estimate the radius of a circle that would encompass 99% of each patch of settled eggs (the egg dispersal radius). Also, egg release was quantified every 2 h during the tidal cycle. A significantly larger egg dispersal radius (P < 0.02) was found for F. spiralis than F. vesiculosus, and this difference was somewhat site dependent with a greater difference between species in exposed sites. The egg dispersal radius was negatively correlated with significant wave height and positively correlated with sea surface temperature for both the species (P < 0.05), with a greater effect of both the factors for F. spiralis than for F. vesiculosus. Egg release during the tidal cycle was variable between species and experiments, with F. vesiculosus releasing more eggs, later in the day, and at a lower tide, than F. spiralis, which released fewer eggs, throughout the day and at all tides. The dioecious species, F. vesiculosus, may have developed a specific adaptation for timing the egg release to periods when emersed in exposed habitats to avoid rapid dilution of gametes that require outcrossing for fertilization. On the other hand, egg release for F. spiralis, which can self-fertilize, occurred both when emersed and immersed, suggesting this species has developed less synchrony with specific environmental factors. Site dependence also suggests local wave conditions can modulate timing of release. The data are consistent with the relaxation of the selective constraints of water motion on fertilization success in a selfing hermaphrodite, relative to an obligate outcrossing species. Results support the idea that species with different mating systems evolve different sensitivities to environmental cues for gamete release with specific implications for inbreeding and successful external fertilization in the ocean.     

Larval behavior of predacious sister-species: orientation,molting site,and survival in Chrysopa

Field and laboratory studies compared two features of larval behavior in a pair of predacious sisterspecies of green lacewings: one (Chrysopa slossonae) a specialist on a single species of colonial aphids (the woolly alder aphid) that occur on branches and trunks of alder trees, the other (C. quadripunctata) a general aphid feeder whose primary prey is dispersed on foliage of diverse types of trees. First, a few hours after hatching, larvae of the two species develop significantly different phototactic responses; the differences correspond well with the spatial distributions of their prey. Most C. slossonae exhibited negative phototaxis, a response that helps move hatchlings inward on alder trees toward the woolly alder aphid colonies, whereas most C. quadripunctata hatchlings showed positive orientation to light, a response that tends to keep them in tree canopies with their prey. Second, in greenhouse experiments, a significantly greater proportion of C. slossonae larvae (second instars) molted within woolly alder aphid colonies and remained with the aphids than did C. quadripunctata larvae. These differences indicate that the specialist larvae have evolved a high degree of behavioral fidelity to their prey. However, larvae (second instars) of the two species that were released near ant-tended woolly alder aphid colonies in the field had similar recovery (= survival) rates. Consequently, natural selection may not act on behavioral traits that influence larval fidelity to prey during the late second and early third instars.     

Brooding behaviour and reproductive success in two species of free-living simultaneous hermaphrodites

Although polyclads are amongst the most structurally simple of the triploblastic metazoans, they adopt a wide range of reproductive strategies. Parental care behaviour in this group is yet to be quantified for any species. We assessed the significance of brooding behaviour to the reproductive success of two free-living marine flatworms. Echinoplana celerrima and Stylochus pygmaeus were collected from the field and placed in pairs in containers of filtered seawater where they laid batches of eggs. Both parents were then removed from half of the containers and the brooding behaviour and hatching success of eggs were quantified. There were interspecific differences in brooding behaviour. Egg masses were covered by one E. celerrima parent for 12 ± 2% of time, whereas egg masses of S. pygmaeus were covered by one or both parents simultaneously for 85 ± 8% of time. Egg batches were abandoned by both species immediately prior to the onset of hatching (10–12 days). Hatching success was generally high (~90%) and brooding did not enhance the hatching success of eggs. We assessed the significance of parental care to hatching success of E. celerrima egg masses in the presence of three potential egg predators; in the presence of other organisms. E. celerrima devoted less time to brooding; however, hatching success was not affected. The amount of time spent brooding eggs differed greatly between the two polyclad species but was not essential to their reproductive success under benign conditions. Parental care may be of adaptive value under more stressful environmental conditions commonly experienced in estuarine environments such as lowered salinity, increased hypoxia or turbidity. Covering egg batches may play an additional role of advertising sexual status and a willingness to care for eggs.     

Larval growth in the estuarine crab Chasmagnathus granulata: the importance of salinity experienced during embryonic development, and the initial larval biomass

The importance of salinity experienced during embryonic development and initial larval biomass on larval growth was studied in the South American estuarine crab Chasmagnathus granulata. Ovigerous females were maintained at three salinities (15, 20, and 32‰) from egg laying to hatching of zoea l. Larvae from all treatments were reared under constant conditions of photoperiod (12∶12), temperature (18°C), and salinity (first instar at 20‰, subsequent instars at 32‰). Biomass was measured as dry weight, carbon, and nitrogen content per individual at egg laying, hatching of zoea l, premoult zoea l, and zoea 4, and in 8-day-old megalopa. From hatching to premoult zoea 4, biomass was higher for larvae from prehatching salinities of 15 and 32‰. There was a significant positive correlation between biomass at hatching and at premoult zoea l and zoea 4. Accumulated biomass during zoeal stages tended to be higher for larvae from broods with higher biomass at hatching, although this trend was not always significant. Zoea 4 either directly metamorphosed to megalopa or moulted to zoea 5, following, respectively, a short or long developmental pathway. The proportion of zoea 4 that followed the long pathway was negatively correlated with biomass of zoeal stages. Biomass at hatching was correlated with biomass of megalopae developed through the short pathway, although it was not correlated with the accumulated biomass at this stage. Megalopae developed through the long pathway (i.e. metamorphosed from zoeae 5) had higher biomass than those from the short pathway. The present results suggest that prehatching salinity and initial egg and larval biomass can be very important for larval growth. Published online: 9 August 2002     

Energy substrates for eggs and prefeeding larvae of the dolphinCoryphaena hippurus

Changes in the chemical composition of developing dolphin (Coryphaena hippurus) eggs and prefeeding yolksac larvae were determined in order to estimate probable dietary requirements of first-feeding larvae. Daily dry matter, protein nitrogen (PN), non-protein nitrogen (NPN), lipid, gross energy content, fatty acid and amino acid profiles from Day 1 to Day 2 eggs and Day 1 to Day 3 larvae were compared. Lipid was the primary endogenous energy source accounting for the daily caloric deficit through both the egg and larval stages, except over the day of hatching. The catabolism of lipid by embryos (0.078 cal d^–1) was greater than that by yolksac larvae (0.036 cal d^–1). The higher demand for energy by embryos was related to a greater rate of protein synthesis during the egg stage. The ratio of PN:NPN increased during egg development without change in total nitrogen content, but was constant throughout the yolksac larvae period. The lipid content per embryo did not decrease over the hatching period (Day 2 to 3, postspawning). However, there was a loss in amino acid content not totally accounted for by sloughing of the chorion at hatching. This loss, as protein, accounted for 0.053 cal of gross energy, which represented 70% of the total estimated energy needs of the fish over this period. Loss of non-essential amino acids (25%) was higher than that of essential amino acids (13%). Proline and tyrosine accounted for 32% of the total loss of amino acids at this time. The only preferential use of fatty acids over any period was a small but significant drop in the content of C22:6n-3 prior to the onset of feeding (Day 5, postspawning). It is speculated that the pattern of energy-substrate use of first-feeding dolphin larvae will reflect the pattern of endogenous energy use during the egg and prefeeding yolksac larval stages. Diets or feeding regimens with lipid as the primary energy source, and containing a fatty acid profile similar to that of eggs or yolksac larvae, should be useful in culturing this species, at least during the early feeding stages.