Spawning behaviour,egg and larval development of the myctophid fish Benthosema pterotum

The distribution of eggs and early larval stages of the myctophid fish Benthosema pterotum was studied during three cruises to the Gulf of Oman during January to February 1981 and February 1983. The eggs and yolk sac larvae were identified and described after artificial fertilization on board the Research Vessel Dr. Fridtjof Nansen. The mature fish spawn in the Gulf at 300 to 100 m depths during early night. The eggs and smallest larvae were found at 300 to 200 m depths. The eggs hatch within 12 h at 21°C. Hatching occurs before the slightly bouyant eggs reach the upper 50 m of the water column.     

Individual effects and interactions of salinity,temperature, and zinc on larval development of the grass shrimp Palaemonetes pugio. I. Survival and developmental duration through metamorphosis

Larvae of the estuarine grass shrimp Palaemonetes pugio (Holthuis) were reared from hatch through successful completion of metamorphosis in 80 combinations of salinity (3 to 31%), temperature (20° to 35°C), and zinc (0.00 to 1.00 ppm Zn⁺⁺). Response-surface methodology was employed to depict the individual effects and interactions of the three factors on survival and developmental duration through total larval development. Outside the optimal salinity-temperature conditions of 17 to 27 S and 20° to 27°C, viability of larvae was reduced by both the individual effects of salinity and temperature and interactions between the two factors. Survival capacity of larvae and resistance adaptations to salinity and temperature were progresively reduced by zinc concentrations from 0.25 to 1.00 ppm Zn⁺⁺. Response-surface analysis of the data suggested that the duration of total larval development of P. pugio was least at salinities from 18 to 23 and at temperatures from 30° to 32°C. At both higher and lower salinity-temperature conditions and in increasing zinc concentrations from 0.25 to 1.00 ppm Zn⁺⁺, developmental rates were retarded. A significant zinc-temperature interaction existed, whereby increasing zinc concentrations reduced both survival and developmental rates of larvae more at suboptimal temperatures. Larval resistance to zinc toxicity was least at supraoptimal salinities, indicative of a significant zinc-salinity interaction. The reduced viability, restricted euryplasticity, and retarded developmental rates of P. pugio larvae developing in media with low-level zinc contamination would limit the distributive properties of the pelagic phase in the life cycle of the species and reduce recruitment both into and out of the parent estuarine population.     

Développement larvaire de deux Tellinacea,Scrobicularia plana (Semelidae) et Donax vittatus (Donacidae)

Scrobicularia plana Da Costa and Donax vittatus L. were reared in the laboratory through settlement. Fertilizable eggs were obtained by perfusing the ovary with 5% 0.1 M ammonium hydroxyde in sea water. S. plana eggs have a thick chorion, inside which the early larval stages develop; they hatch as straight-hinge larvae more than 60 h after fertilization. This brood protection is considered to be an adaptation to osmotic pressure changes and pollution in the environment. D. vittatus eggs have a very thin chorion and are unprotected. Further development is planktotrophic and very similar for the two species. Under laboratory conditions, the pediveliger stage is attained 3 weeks after fertilization and settlement occurs 1 week thereafter. S. plana spat stop growing until a suitable substratum is available. Meanwhile they undergo a byssus drifting important for postlarval dispersion. Post larvae resume growth as soon as a small quantity of fine sand is added to the rearing jar. The exhalant siphon is developed first, when the post larvae reach a length of 600 m; the inhalant siphon is formed later, at a length of approximately 900 m. Evolution from the larval hinge to the juvenile hinge stage occurs sooner in S. plana than in D. vittatus. Comparison of laboratory larval development with field development indicates that spawning occurs in June and August for S. plana in North Wales (UK).     

The influence of temperature on the development of Baltic Sea sprat (Sprattus sprattus) eggs and yolk sac larvae

In spring 2004 and 2005 we performed two sets of experiments with Baltic sprat (Sprattus sprattus balticus Schneider) eggs and larvae from the Bornholm Basin simulating ten different temperature scenarios. The goal of the present study was to analyse and parameterise temperature effects on the duration of developmental stages, on the timing of important ontogenetic transitions, growth during the yolk sac phase as well as on the survival success of eggs and early larval stages. Egg development and hatching showed exponential temperature dependence. No hatching was observed above 14.7°C and hatching success was significantly reduced below 3.4°C. Time to eye pigmentation, as a proxy for mouth gape opening, decreased with increasing temperatures from 17 days post hatch at 3.4°C to 7 days at 13°C whereas the larval yolk sac phase was shortened from 20 to 10 days at 3.8 and 10°C respectively. Maximum survival duration of non-fed larvae was 25 days at 6.8°C. Comparing the experimental results of Baltic sprat with existing information on sprat from the English Channel and North Sea differences were detected in egg development rate, thermal adaptation and in yolk sac depletion rate (YSDR). Sprat eggs from the English Channel showed significantly faster development and the potential to develop at temperatures higher than 14.7°C. North Sea sprat larvae were found to have a lower YSDR compared to larvae from the Baltic Sea. In light of the predictions for global warming, Baltic sprat stocks could experience improved conditions for egg development and survival.     

Effects of temperature on oxygen consumption,growth, and development of embryos and yolk-sac larvae of Siganus randalli (Pisces: Siganidae)

Eggs from laboratory spawnings of the coralreef fish Siganus randalli Woodland were incubated at two temperatures (27 and 30 °C). Eggs and larvae were sampled until larval starvation, while changes in oxygen consumption, growth, yolk utilization, and development were monitored. Oxygen consumption, which peaked at hatching, was higher for embryos incubated at 30 °C than at 27 °C. Rates of oxygen consumption (nl h^-1 individual^-1) at hatching were similar to those for other temperate and tropical species. Rates of oxygen consumption by yolk-sac larvae were highly variable, and these data suggest that larval oxygen consumption prior to yolk-sac absorption may not be significantly influenced by temperature. Rates of yolk depletion were higher for larvae at the higher temperature. After an initial rapid increase in length, length of larvae at 30 °C decreased with age. Egg size, egg weight, and maximum notochord length of larvae differed significantly between spawns. Age-specific oxygen consumption rates by the embryos varied between spawns, but regressions describing oxygen consumption as a function of age did not differ significantly. The initiation and completion of eye pigmentation were used as developmental markers to calculate the amount of yolk remaining for larvae at the different temperatures. Larvae maintained at 30 °C completed eye pigmentation approximately 3 h sooner than those maintained at 27 °C, but had less endogenous reserves. This finding indicates a trade-off between rapid development and efficient utilization of the endogenous reserves. The completion of eye pigmentation in larvae incubated at the higher temperature occurred at midnight and, depending on the amount of time that the larvae have to initiate feeding prior to the point-of-no-return, the timing of completion of eye pigmentation could influence larval survival.     

Changes in yolk total proteins and lipid components and embryonic growth rates during lobster (<Emphasis Type="Italic">Homarus americanus</Emphasis>) egg development under a simulated seasonal temperature cycle

From August 2000 to June 2001, seven egg-carrying female lobster (Homarus americanus) from the Îles de la Madeleine population (Gulf of St. Lawrence, Canada) were held under a simulated seasonal temperature cycle to monitor egg development from extrusion to hatching. For the first time, changes in the yolk components (total lipids and major lipid classes, total proteins) and embryo growth of single eggs were monitored separately over the entire development period. Under the controlled temperature conditions, egg development proceeded in three phases. (1) Autumn, from extrusion to early December, was marked by a rapid increase in the Perkinss eye index and rapid declines in yolk total proteins and triacylglycerols (TAG). Embryo daily growth rate was estimated between 1 and 2 µg proteins day^–1. (2) Winter, from late December to early April (temperature stable at ca. 1°C) was characterized by a stationary phase in the evolution of the eye index and yolk lipid use, and embryo growth slowed significantly. (3) Spring, from late April to hatching in June was the period with the most rapid changes in yolk TAG and embryo growth rates >6 µg proteins day^–1 were recorded. Almost 65% of the live biomass (total proteins) of the hatching larvae was accumulated during the last few weeks of development. An index of embryo growth efficiency was estimated as the slope of the relationship between embryo total proteins and yolk TAG during egg development. A relationship was found between the initial mean egg dry weight and the embryo growth efficiency index suggesting that under the same experimental conditions bigger eggs used yolk lipids more efficiently and sustained faster embryonic growth than smaller eggs. The relationship may also explain why larger larvae originate from larger eggs.Communicated by R.J.Thompson, St Johns     

Quantitative and ultrastructural studies on the reproductive biology of the polychaete Pholoe minuta in Galway Bay

Previous works by the present authors have identified, in a qualitative fashion, the reproductive cycle of Pholoe minuta (Fabricius) in inner Galway (53°13.5N; 9°7W). This quantitative, histological study, carried out over the period late May 1981 to late April 1982, shows that P. minuta is polytelic (two to three annual spawnings in an individual's lifespan). Individuals become sexually mature for the first time when approaching 3 yr of age. Estimates were made of the size of the reproductively active population (47 to 49%), sex ratio (1:1), duration (10 to 11 mo) and pattern (unimodal) of gametogenesis and fecundity levels (210 198 eggs m^-2). Maturation (mean oocyte size=85 m) and spawning (for 1 wk during late March through early April) were shown to be synchronised. Throughout oogenesis, follicle cells play an important role in binding together oocyte clusters, and desmosomal contacts are evident between oocyte and follicle cell plasmalemmas. No evidence for the synthesis of yolk precursors in the follicle cell cytoplasm was discovered. Oocytes are rich in Golgi apparatuses (yolk synthesising) and nuclear pores are numerous. Rough endoplasmic reticulum is distended in nature. Egg envelope development does not appear to commence until after the onset of vitellogenesis. Mature spermatozoa are of the primitive bullet-shaped type, with an unmodified acrosome. A possible method of elevation membrane formation is described.     

Acclimation and tolerance of Artemia salina to copper salts

The brine shrimp Artemia salina L. was acclimated in sea water with cupric chloride, acetate, carbonate, and sulphate, each at concentrations of 0.1, 0.05 and 0.025 ppm Cu⁺⁺, together with sea water controls. Growth inhibition was observed in all four compounds, generally in direct relationship to the concentration. It was least in sulphate, and increased progressively in chloride, acetate and carbonate in that order. No inhibition however was observed in carbonate at 0.025 ppm Cu⁺⁺. In toxicity tests, 2-week old larvae from each solution were exposed to concentrations of 10, 7.5, 5, 2.5 and 1 ppm Cu⁺⁺ of the same compounds, together with unacclimated larvae of the same age. Similar tests were held with 6-week old adults acclimated (a) in 0.1 ppm Cu⁺⁺ (chloride, acetate and sulphate) using the same concentrations and (b) in 0.5 ppm Cu⁺⁺ (carbonate), using 150, 125, 100, 75, and 50 ppm Cu⁺⁺. Toxicity to unacclimated larvae and adults differed with the compounds, carbonate being the least toxic, followed by sulphate, chloride and acetate in increasing order. Larvae acclimated in chloride (0.025 ppm Cu⁺⁺) and sulphate (0.1 and 0.5 ppm Cu⁺⁺) showed an increased tolerance to 1 and 2.5 ppm Cu⁺⁺ compared to untreated controls. Tolerance was not enhanced from 5 ppm Cu⁺⁺ upwards. In both compounds, adults acclimated in 0.1 ppm Cu⁺⁺ showed an increased tolerance to concentrations between 1 and 7.5 ppm Cu⁺⁺ compared to controls. Larval mortality in carbonate was below 50% in all test solutions. Adults acclimated at 0.5 ppm Cu⁺⁺ showed an increased tolerance to 50 ppm Cu⁺⁺ compared to controls. Considerable precipitation occurred with the high levels of this compound, thus effecting the final concentrations. No acclimation effect was observed in acetate for either larvae or adults. It is suggested that in A. salina, copper toxicity depends on the particular form of the metal, and that this difference is also evident in growth inhibition and in the potential acquisition of increased tolerance through exposure to low concentrations.     

Sex ratio manipulation in response to maternal condition in pigeons: evidence for pre-ovulatory follicle selection

A number of recent reports have documented offspring sex ratio biases in birds. However, to date the potential mechanisms that have been put forward to explain the proximate basis for these deviations are entirely speculative. Using a captive population of domestic pigeons (Columba livia domestica), I tested the hypothesis that mothers in relatively poor physical condition should overproduce daughters by manipulating maternal body condition around the time of egg laying by continuous egg removal and differing feeding regimes. During treatment, females were fed a controlled quantity of food. This, combined with the high energetic costs of repeated egg production caused a significant reduction in maternal body weight. In contrast, during control when food was available ad libitum, maternal body weight did not decline, despite repeated egg production. No significant deviation from parity was evident in the sex ratio of either the first or second eggs during control, whereas during treatment a significant female bias was evident in not only the first egg, but also in the second egg. The absence of single-egg clutches, the rarity of infertile eggs and the lack of laying delays between eggs strongly suggests that the mechanism of sex ratio adjustment in pigeons occurs prior to ovulation. The highly skewed sex-distribution within the two-egg clutches and the unexpectedly large amount of variation in the yolk weight of eggs produced during treatment (but not control) are consistent with the expectations of pre-ovulatory selective resorption of wrong sex ovarian follicles.     

Determination of copper in embryos and very young specimens of Sepia officinalis

The total amount of copper in embryos and newly hatched young individuals of Sepia officinalis L. has been determined by microtechnique, using bathocuproine-sulfonate as complexing reagent. During embryonic life, the total amount of copper does not change; it remains at a level close to 3.8 g. The copper is found in the yolk sac of very early embryos; it is subsequently transferred into the embryo proper. After hatching, the copper content diminishes quickly in starved individuals. Fed S. officinalis also usually lose copper. The reason for this may be that the inner yolk sac of newly hatched individuals contains a great deal of the total copper, which is excreted with the yolk after the latter has become superfluous. Later on, copper must be taken up from the food. The mobilization of protein and copper from the yolk into the blood may account for the early appearance of embryonic hemocyanin in the blood.     

Reproductive competition in queenless honey bee colonies (Apis mellifera L.)

Previously we reported that there are subfamily differences in drone production in queenless honey bee colonies, but these biases are not always explained by subfamily differences in oviposition behavior. Here we determine whether these puzzling results are best explained by either inadequate sampling of the laying worker population or reproductive conflict among workers resulting in differential treatment of eggs and larvae. Using colonies composed of workers from electrophoretically distinct subfamilies, we collected samples of adult bees engaged in the following behavior: true egg laying, false egg laying, indeterminate egg laying, egg cannibalism, or nursing (contact with larvae). We also collected samples of drone brood at four different ages: 0 to 2.5-h-old eggs, 0 to 24-h-old eggs, 3 to 8-day-old larvae, and 9 to 14-day-old larvae and pupae. Allozyme analyses revealed significant subfamily differences in the likelihood of exhibiting egg laying, egg cannibalism, and nursing behavior, as well as significant subfamily differences in drone production. There were no subfamily differences among the different types of laying workers collected from each colony, suggesting that discrepancies between subfamily biases in egg-laying behavior and drone production are not due to inadequate sampling of the laying worker population. Subfamily biases in drone brood production within a colony changed significantly with brood age. Laying workers had significantly more developed ovaries than either egg cannibals or nurses, establishing a physiological correlate for the observed behavioral genetic differences. These results suggest there is reproductive conflict among subfamilies and individuals within queenless colonies of honey bees. The implications of these results for the evolution of reproductive conflict, in both queenright and queenless contexts, are discussed.     

Selective particle ingestion by oyster larvae (Crassostrea virginica) feeding on natural seston and cultured algae

I investigated selective particle ingestion by oyster larvae (Crassostrea virginica) feeding on natural seston from Chesapeake Bay and laboratory-cultured algae of different sizes or chemical content. In 15 of 16 experiments with complex natural suspensions as food, small(<150 m) and large (>150 m) larvae selected most strongly for small (2 to 4 m) food particles, but in the presence of a large (>10 m)-cell dinoflagellate bloom, large larvae strongly selected much larger (22 to 30 m) food material (presumably dinoflagellates). When fed simplified mixtures of four cultured algal species (Synechococcus bacillaris, Isochrysis sp., Dunaliella tertiolecta, and Prorocentrum minimum) ranging in size from 1 to 11 m, small larvae preferred 1 m algae while large larvae preferred 11 m algae. In experiments with algal mixtures, and with suspensions of natural particles and added algae, large larvae preferred algal species harvested from exponential-phase cultures over other species from stationary-phase cultures. Larval ingestion rates of the cultured alga Thalassiosira pseudonana were about three times higher for cells with a low carbon:nitrogen ratio (7.2:1) than for high C:N ratio (16.2:1) cells when these cells were offered separately in suspensions of equal concentration. As a result, more algal cells, algal C, and algal N was ingested by larvae fed low C:N cells. However, larvae did not show a significant preference for either type of cell when they were offered in a 1:1 cell mixture. Feeding patterns of C. virginica larvae in natural food suspensions can vary with the composition of these complex suspensions, and ingestion seems dependent not only on the size, but on the growth rate and chemical quality of food particles.     

Time-dependent shifts between infanticidal and parental behavior in female burying beetles a mechanism of indirect mother-offspring recognition

Summary Female burying beetles Necrophorus vespilloides Herbst (Coleoptera: Silphidae) were allowed to lay eggs on a carcass and their subsequent behavior towards larvae added to the carcass was observed. Females did not discriminate against unrelated larvae if these were added within an hour after the females' own first larva had hatched (at the right time). Changing the spatial surroundings of the carcass had no effect on the females' readiness to exhibit care behavior. Neither did the age of the larvae added or the condition of the carcass affect the onset of maternal care. However, the females' response to larvae encountered was strongly time-dependent: most females killed and ate larvae that could not have hatched from their own eggs because they were added long before their own larvae hatched. The proportion of females accepting larvae added to early increased as the time their own larvae hatched approached. Larvae added to the carcass 2 or 3 days after the test females' own first larva had hatched were always accepted by females that had already started to feed larvae, but were often killed by females that were not feeding larvae. In the latter group of females, the tendency to kill larvae added was most pronounced if the females had already started to produce a second clutch of eggs at the time larvae were added. Offprint requests to: J.K. Müller     

The importance of free amino acids to the energy metabolism of eggs and larvae of turbot (Scophthalmus maximus)

A study was undertaken to establish the role of free amino acids (FAA) in aerobic energy dissipation in embryos of turbot (Scophthalmus maximus) which contain an oil globule in the egg. Laboratory-reared developing eggs and larvae (15°C, 34 salinity) were measured for oxygen uptake, ammonia excretion, contents of FAA, protein, and ammonium, and volumes of yolksac and oil globule. Newly spawned eggs from different batches contained 55 to 90 nmol egg^–1 of FAA. Resorption of FAA occurred in parallel with the consumption of yolk. Resorption of the oil globule, however, occurred predominantly after hatching and mainly after yolk resorption. The combined data suggest that approximately 70% of the FAA are utilized as an energy substrate, while the rest are polymerized into body proteins. FAA become a significant energy substrate in the early egg stage and account for 100% of the aerobic energy dissipation 2 d after Fertilization then decrease to ca. 60% at the time of hatching. Lipids derived from the oil globule seem to be the main fuel after hatching and account for ca. 90% of the energy dissipation at the onset of first-feeding. Thus, the energetics of fish embryos which contain an oil globule seems to be different from those that depend exclusively on the nutritional reserves of the yolk.     

Laboratory rearing of the clupeid fish Harengula pensacolae from fertilized eggs

Pelagic eggs of the scaled sardine Harengula pensacolae (Goode and Bean), have been hatched and reared in the laboratory for the first time. Larvae were reared in two 75 l aquaria under constant illumination, at an average temperature of 26.2°C. Zooplankton collected in a 35 mesh net was fed to the newly hatched larvae, and the diet was supplemented later with Artemia salina nauplii and a pelleted food. Larvae hatched at 4 mm TL (total length), and metamorphosed about 25 days later at 25 to 30 mm TL. Survivors averaged 76 mm TL 100 days after hatching. Of the 500 incubated eggs, 2.8% survived until 20 days, after which no significant natural mortality occurred. Sources of natural mortality included starvation, a copepod parasite (Caligus sp.), and injuries from contact with the sides of the tank. Larvae began feeding at 4.5 mm TL on copepod nauplii averaging 62 in body width. Scaled sardines were photopositive throughout the larval stage.Contribution No. 149, Bureau of Commercial Fisheries Tropical Atlantic Biological Laboratory, Miami, Florida 33149, USA.     

Studies on sharks. I. Reproduction in the female sumitsuki shark Carcharhinus dussumieri

During the last 5 years, the T.S. Nagasaki Maru, Nagasaki University, Japan, carried out trawling operations in the waters off Kuching, northwest Borneo, for 1 week in July of each year. During this period, 119 specimens of the sumitsuki shark Carcharhinus dussumieri Valenciennes (Müller et Henle, 1841) were caught and their reproductive system investigated. In these waters, C. dussumieri has no definite reproductive seasons; it was, therefore, possible to obtain sufficient suitable material to examine all stages of the sexual cycle. The left ovary is rudimentary throughout the life cycle, and only the right ovary is functional. The ova in the ovary are already developing for the succeeding ovulation while the embryo already present in the uterus is growing; the 2 mature eggs from the right ovary are ovulated in the peritoneal cavity soon after parturition. The developing ova which remain in the ovary after ovulation are reabsorbed. The 2 mature eggs ovulated enter a common ostium and each oviduct receives one egg. In the nidamental gland, the fertilized egg is enclosed by an embryonic membrane and descends into the uterus where it grows into an embryo (simple pregnancy: 1 embryo in each uterus). During earlier embryonic development, nourishment is obtained from the yolk stored in the yolk sac. The placenta is established when the embryo attains a total length of about 150 mm; the embryo is thenceforth nourished by the placenta through the umbilical stalk until birth.     

Yolk utilization and hatching time in the Canadian lobster Homarus americanus

During the course of its embryonic development, the Canadian lobster Homarus americanus Milne-Edwards exhibits steady increases in water content (56.2 to 86.8%) and ash (5.8 to 21.2%), and a progressive decrease in energy content from 6636 to 4292 cal/g dry weight. Mean dry weight of a single egg is 965 g, equivalent to 6.4 cal; a freshly hatched egg. The lobster hatches about 1,500 larvae per night over a period of 4 to 5 days. Dry weight, ash and calorific contents of larvae hatched on different days show considerable variations. After larvae hatch on the first day, continuous salt absorption by eggs to hatch on subsequent days leads to a steady increase in ash content from 143 g/larva hatched on the first day to 255 g/larva hatched on the fourth day, and consequently, to an increase in dry weight from 854 to 956 g/larva. Metabolism of embryos (0.1 cal/day), which are yet to be hatched on subsequent days, depletes the calorific content per unit weight (from 4637 to 3837 cal/g dry weight) as well as per larva (from 3.98 to 3.67 cal).Dedicated to my colleague K.-H. Schumann (Biologische Anstalt Helgoland) who died on December 12, 1969 due to a diving accident.     

Biologie d'un copépode des mares temporaires du littoral méditerranéen français: Eurytemora velox

The reproduction of Eurytemora velox, a brackish copepod from temporary lakes of the south of France, was studied in winter and spring 1978, under various temperature and salinity conditions, using Chlorella sp. and Amphidinium sp. as food. Maximum numbers of successive eggs sacs (9), eggs per sac (39.3) and total egg production per female (311) were recorded for the witner generation, only 4.8, 34.8 and 109, respectively, for the spring generation. In contrast, the number of eggs per female per day was highest (11.3) in the spring generation, which displayed a more rapid reproductive cycle. Despite strong individual variations in the rhythm of egg sac production and in abundance of eggs per sac, egg production was generally higher during the first third of adult life, attaining a maximum after production of the second or the third egg sac. The continuous presence of the males was necessary to assure complete fertilization of eggs throughout the whole life of adult females. Hatching rate displayed high individual variability, in particular for the spring generation, which had lower average hatching rates (between 0 and 26%, depending on salinity or temperature) than the winter generation (14 to 64%). These differences may be related to the ability of E. velox to produce resting eggs during spring, allowing the species to maintain itself in a temporary water milieu. Temperature significantly affected longevity and daily egg production of females; presence or absence of males did not affect these parameters. An increase in salinity from 20 to 30%. reduced longevity, number of egg sacs, and daily egg production in the winter generation, but not in the spring generation. The specific daily production of females during their adult life was calculated from the egg production:biomass ratio of females, in carbon units. In the winter generation, this ratio increased between 10° and 15°C compared to ratios between 15° and 20°C; the opposite was observed for the spring generation. The seasonal differences in the effects of temperature and salinity on reproduction could indicate an adaptation mechanism to the strongly thermal and haline seasonal fluctuations which characterize the habitat of Ex. velox (brackish waters, drying-up in summer). Larval mortality was high, except at 20%. S for the spring generation. The sex-ratio of the offspring was unaffected by variations in breeding conditions. Hatching time and development time of larvae could be described by two Blehrádek equations displaying close b and () coefficients. We calculated the energy balance of adult females from data obtained in a previous study on feeding and respiration in E. velox, and this is discussed in context with the egg production results. Net growth efficiency varied with algal concentration according to an asymptotic curve, reaching a maximum of 0.43 with Tetraselmis maculata as food or 0.53 with Amphidinium sp. Actual egg production rate obtained in the present study was in good agreement with that calculated by the difference between assimilated food and respiration expenses.     

Water and salt balance of halibut eggs and larvae (Hippoglossus hippoglossus)

Eggs of halibut [Hippoglossus hippoglossus (L.)] have a negative buoyancy in sea water of 35 S, in contrast to eggs of most flatfish species. The cause of this was investigated. The osmolality of the yolk is 350–420 mOsm during embryonic development. This is within the range for marine teleost serum and for yolk of pelagic eggs. Concentrations of major inorganic ions are comparable with those of pelagic plaice eggs [Pleuronectes platessa (L.)]. The values for Na⁺, K⁺ and Cl^- are 6, 85, and 64 mmol · (1 H₂O)^-1 after fertilization, and at the time of hatching the corresponding values are 17, 11, and 80. Large amounts of other inorganic constitutents are excluded for osmotic reasons. Malfunction in the regulation of osmolality or of inorganic constituents is thus unlikely to be the cause of negative buoyancy. The relative dry weight of the chorion (egg shell) in halibut eggs is less than in several pelagic egg types, excluding the chorion as the main contributor of negative buoyancy. It is concluded that a high content of organic matter in the rest of the egg is the cause of the negative buoyancy.     

Investigations on the biology of Branchiostoma senegalense larvae off the northwest African coast

Branchiostoma senegalense Webb spawns from April to June off the coast of the Spanish Sahara between 23° and 26°N. The larvae drift in a southerly direction, and occur in large numbers off Cap Blanc (20° 55N; 17° 22W) from June to December. The gut contents of 3,300 larvae taken from 22 samples were investigated. There was no food in the gut of 18% of these larvae. Phytoplankton (Thalassiosira gravida, Nitzschia seriata, Coscinodiscus eccentricus, Dinophysis acuminata etc.) were found in the gut of the remaining 82%. The guts of three larvae also contained crustaceans (a cyclopoid, a harpacticoid, and an isopod). Since all three crustaceans showed no signs of having been digested, the authors conclude that they actively penetrated into the larvae and were not eaten. Plankton samples were taken from various depths (55 to 25 m and 25 to 0 m) daily (7.30, 12.30, 19.00, 0.15 hrs) at an anchor station, over a period of 10 days. There was no evidence of a diurnal vertical migration of B. senegalense larvae. The larvae were found in various numbers at all depths. No larvae were found on the bottom itself. The larvae of B. senegalense are, thus, genuine plankton organisms.