Yolk-sac Larvae Research Articles

Inter-annual and inter-specific differences in the drift of fish eggs and yolksac larvae in the North Sea: A biophysical modeling approach

We employed 3-D biophysical modeling and dispersion kernel analysis to explore inter-annual and inter-specific differences in the drift trajectories of eggs and yolksac larvae of plaice (Pleuronectes platessa), Atlantic cod (Gadus morhua), sprat (Sprattus sprattus) and horse mackerel (Trachurus trachurus) in the North Sea. In this region, these four species exhibit peak spawning during the boreal winter, late winter/early spring, late spring/early summer, and mid-summer respectively, but utilize the same spawning locations (our simulations included Dogger Bank, Southern Bight and the German Bight). Inter-annual differences in the temperature history, and an increase in the area of dispersion and final distribution at the end of the yolksac phase were more pronounced (and related to the North Atlantic Oscillation) for winter- and early spring-spawners compared to late spring/summer spawners. The progeny of the latter experienced the largest (up to 10-fold) inter-annual differences in drift distances, although absolute drift distances were modest (~2 to 30 km) when compared to those of the former (~ 20 to 130 km). Our results highlight the complex interplay that exists between the specific life history strategies of the different species and the impacts of the variability in (climate-driven) physical factors during the earliest life stages of marine fish. Resumen: Diferencias interanuales e interespecificas en la deriva de huevos y larvas lecitotroficas en el mar Norte: Aproximacion a traves un modelo biofisico. – En este trabajo utilizamos un modelo 3-D fisico-biologico y un analisis de dispersion del nucleo para investigar las diferencias interespecificas e interanuales en las trayectorias de la deriva de huevos y larvas lecitotroficas de la solla (Pleuronectes platessa), el bacalao Atlantico (Gadus morhua), el espadin (Sprattus sprattus) y el jurel (Trachurus trachurus) en el Mar del Norte. En esta region, las especies estudiadas muestran distintos picos de distintos desoves en el tiempo: invierno boreal, invierno tardio/primavera temprana, primavera tardia/verano temprano y mitad del verano, respectivamente, aunque comparten las mismas zonas de desove. Las simulaciones efectuadas corresponden a tres de estas zonas: Dogger Bank, Southern Bight y German Bight. Los resultados mostraron diferencias interanuales en la temperatura experimentada por las larvas, en el area de dispersion y en el patron de distribucion al final del estadio lecitotrofico, que fueron mas evidentes en el bacalao Atlantico, en comparacion con el espadin. Asi mismo, estos factores estuvieron correlacionados con la Oscilacion del Atlantico Norte. La progenie del espadin, ademas, mostro la mayor variacion interanual en la distancia de dispersion, siendo hasta 10 veces mayor, aunque la distancia absoluta alcanzada fue relativamente modesta (~2-30 km) en comparacion con la observada para el bacalao Atlantico (~20-130 km). Nuestros resultados subrayan la compleja interaccion que existe, durante los estadios tempranos del desarrollo de peces marinos, entre las estrategias ecologicas

Using drift nets to capture early life stages and monitor spawning of the Yangtze River Chinese sturgeon (Acipenser sinensis)

A sampling system for capturing sturgeon eggs using a D-shaped bottom anchored drift net was used to capture early life stages (ELS) of Chinese sturgeon, Acipenser sinensis, and monitor annual spawning success at Yichang on the Yangtze River, 1996–2004, before and just after the Three Gorges Dam began operation. Captured were 96 875 ELS (early life stages: eggs, yolk-sac larvae = eleuthero embryos, and larvae); most were eggs and only 2477 were yolk-sac larvae. Most ELS were captured in the main river channel and inside the bend at the Yichang spawning reach. Yolk-sac larvae were captured for a maximum of 3 days after hatching began, indicating quick dispersal downstream. The back-calculated day of egg fertilization over the eight years indicated a maximum spawning window of 23 days (20 October–10 November). Spawning in all years was restricted temporally, occurred mostly at night and during one or two spawning periods, each lasting several days. The brief temporal spawning window may reduce egg predation by opportunistic predators by flooding the river bottom with millions of eggs. During 1996–2002, the percentage of fertilized eggs in an annual 20-egg sample was between 63.5 to 94.1%; however, in 2003 the percentage fertilized was only 23.8%. This sudden decline may be related to the altered environmental conditions at Yichang caused by operation of the Three Gorges Dam. Further studies are needed to monitor spawning and changes in egg fertilization in this threatened population.

Toxication or detoxication? In vivo toxicity assessment of ozonation as advanced wastewater treatment with the rainbow trout

Ozonation as advanced wastewater treatment method is an effective technique for micropollutant removal. However, the application of this method carries the inherent danger to produce toxic oxidation byproducts. For an ecotoxicological assessment conventionally treated wastewater, wastewater after ozonation and ozonated wastewater after sand filtration were evaluated in parallel at an operating treatment plant via the fish early life stage toxicity test (FELST) using rainbow trout ( Oncorhynchus mykiss). The FELST revealed a considerable developmental retardation of test organisms exposed to ozonated WW. This was accompanied by a significant decrease in body weight and length compared to reference water, to the conventionally treated WW and to the ozonated water after sand filtration. Hence sand filtration obviously prevents from adverse ecotoxicological effects of ozonation. An additional test with yolk-sac larvae resulted in a significant reduction of vitellogenin levels in fish exposed to ozonated wastewater compared to fish reared in conventionally treated wastewater. This demonstrates the effective removal of estrogenic activity by ozonation. Adverse ozonation effects may have been a result of the conversion of chemicals into more toxic metabolites. However, sand filtration reduced toxication effects indicating that these oxidation byproducts are readily degradable or adsorbable. The results indicate that in any case ozonation should not be applied without subsequent post treatment appropriate for oxidation byproducts removal (e.g. sand filtration).

Preliminary investigations on the effects of dietary lipid on the spawning performance and egg quality of black sea bassCentropristis striataL

Adult black sea bass Centropristis striata broodstock (N=162) were fed three different dietary treatments: two commercially prepared diets with 45% protein and two different lipid levels (12% and 20%) (diets 1 and 2), and a diet of frozen Atlantic silversides Menidia menidia (SS, diet 3). Broodstock were held under controlled photothermal conditions and induced to spawn with an LHRHa pellet (72 μg kg−1 bw). Dietary lipid had pronounced effects on spawning performance and egg quality. Diet 3 (SS) produced a significantly (P<0.05) higher fertilization success (22.4%) than diets 1 (0.6%) and 2 (4.8%). The hatching success of fertilized eggs was similar in all diets (range=40–58.6%), but only two spawns from diet 1 (12% lipid) yielded viable yolk-sac larvae (YSL). Diet 3 (SS) also produced significantly more YSL per female (21.8 × 103) than the diet 1 (0.3 × 103). Eggs from diet 3 (SS) contained a significantly greater proportion of n-3 series fatty acids, with docosahexaenoic acid (DHA) as the largest fraction. Eggs from commercially prepared dietary treatments contained significantly more n-6 fatty acids. The poor spawning performance of fish fed diet 1 (12% lipid) may be related to higher levels of linoleic acid and lower levels of DHA in the diet.

Variability of Egg Characteristics among Female White Bass and the Relationship between Egg Volume and Length at Hatch of Sunshine Bass

AbstractDomesticated white bass Morone chrysops can be used in selective breeding programs to produce sunshine bass (female white bass × male striped bass M. saxatilis). In addition to fast growth or favorable feed conversion, selection could be based on favorable egg or larval characteristics. Eggs from 12 white bass were fertilized with striped bass sperm to produce sunshine bass larvae and were individually photographed and incubated. The yolk sac larvae hatched from these eggs were also photographed within 3 h of hatching. Percent hatch ranged from 49% to 96%. Egg and larval characteristics were determined from the digital images. Total lipid and fatty acid composition were determined for eggs from each female. Average egg volume ranged from 0.32 to 0.42 mm3. Standard lengths of yolk sac larvae ranged from 2.51 to 3.62 mm. The relation between individual egg volumes and individual standard lengths explained only 1% of the variability in length at hatch. Average egg characteristics were generally unrelated to average length at hatch, but fatty acid composition was related to percent hatch. Maternal effects explained about 11% of the variability in individual length at hatch, and time to hatch (i.e., the length of time from fertilization to hatch for an individual embryo) explained 25% of the variability in individual length at hatch. Some females produced eggs and larvae with characteristics that were more suitable to increasing survival and fingerling production. Selection for these characteristics in broodstock white bass females could lead to improved production of sunshine bass fingerlings.

Larval performance of aquacultured Florida pompano ( Trachinotus carolinus) fed rotifers ( Brachionus plicatilis) enriched with selected commercial diets

Selected rotifer enrichment diets were compared on the basis of growth, survival, and fatty acid content of larval Florida pompano, Trachinotus carolinus L. Two 9-day larval rearing trials were conducted using a recirculating aquaculture system. In Trial 1, two microalgae concentrates ( Isochrysis sp., ISO; and Pavlova sp.), a semi-moist paste (Protein Selco Plus, PS+), and a combination of the three diets were compared. In Trial 2, PS+ and three dry enrichment diets (Ori-Green, OG; Protein HUFA, PH; and AlgaMac 3050, AM) were compared. Larvae were fed rotifers 4 times daily at a rate of 2.5 rotifers/ml/feeding at 2–9 days post-hatch (DPH). Although larval growth in both trials was likely influenced by differences in culture density resulting from variable survival, in Trial 1 at 9 DPH standard length (SL) of larvae fed Pavlova-enriched rotifers (4.60 ±0.39 mm, mean ± SD) was greater ( P < 0.05) than that of larvae fed rotifers enriched with ISO (4.29 ±0.48 mm); and the combined treatment (4.31 ± 0.48 mm) and body depth (BD) of larvae fed Pavlova-enriched rotifers (1.21 ± 0.16 mm) was greater than that of larvae fed rotifers enriched with the combined treatment (1.08 ± 0.18 mm). In Trial 2 at 9 DPH, SL and BD of larvae fed rotifers enriched with PH (5.00 ± 0.23 and 1.24 ± 0.12 mm, respectively) was greater than that of larvae fed rotifers enriched with other diets. Survival of larvae fed rotifers enriched with PS+ was highest in both Trial 1 (24.1 ± 10.2%) and Trial 2 (34.4 ±1.6%) and was significantly greater than that of larvae fed rotifers enriched with Pavlova (7.3 ± 1.6%) and the combined treatment (6.0 ± 1.6%) in Trial 1 and larvae fed rotifers enriched with PH (21.8 ± 6.3%) and AM (14.1 ± 4.9%) in Trial 2. While lipid content and fatty acid composition of PS+ enriched rotifers closely resembled that of pompano yolk-sac larvae, n − 3 HUFA content of PS+ enriched rotifers as well as larvae fed PS+ enriched rotifers was not significantly greater than that of other diets tested in both trials.

The accumulation of substances in Recirculating Aquaculture Systems (RAS) affects embryonic and larval development in common carp Cyprinus carpio

The accumulation of substances in Recirculating Aquaculture Systems (RAS) may impair the growth and welfare of fish. To test the severity of contaminants accumulated in RAS, early-life stages of fish were used. Ultrafiltered water from two Recirculating Aquaculture Systems (RAS), one RAS with a high accumulation of substances (water exchange rate 30 L/kg feed/day) and one RAS with a low accumulation of substances (water exchange rate 1500 L/kg feed/day), was used to incubate eggs and rear larvae of common carp Cyprinus carpio. A broad range of read-out parameters was used to determine the effect of accumulation level on the development of the early-life stages; from hatching dynamics to larvae length and dry weight. The water quality (temperature, pH, dissolved O 2, conductivity, total bicarbonate, ortho-phosphate-P, TAN, NO 2 −–N, NO 3 −–N and minerals) was compared between the 2 treatments. Carp eggs developing in the high-accumulation water had higher mortality percentages (both for eggs and larvae), reduced hatching percentages, delayed hatching dynamics and reduced larvae length and body weight. However, these larvae exhibited fewer deformities than larvae incubated in the low-accumulation water. Furthermore, an accelerated development both of the embryo (appearance of heart beat, pectoral fin bud and tail movement) and yolk-sac larvae (depletion of the yolk sac) was observed in the high-accumulation water. The high-accumulation water had significantly lower pH and higher conductivity, NO 2 −–N, NO 3 −–N and ortho-phosphate-P. Most of the minerals (As, Cu, Mn, Ni, Zn, K, Mg, Na, P and S) including heavy metals, were present at a higher concentration in the high-accumulation water. The influence of these parameters on the embryonic and larval development of fish is discussed. It is suggested that in the high-accumulation water, the concentration of ortho-phosphate-P, nitrate and of the heavy metals arsenic and copper is likely to have impaired the embryonic and larval development and therefore deserves further research as potential growth inhibiting factors in RAS.

A novel approach to controlling dissolved oxygen levels in laboratory experiments

Hypoxia is a widespread environmental stressor that affects marine, estuarine and freshwater systems worldwide. Investigating the effects of hypoxia on aquatic animals in the natural environment is difficult and expensive. Laboratory experiments provide an alternative that allows manipulation of environmental variables and simulation of altered conditions that are expected in the future. However, controlling dissolved oxygen (DO) levels precisely in laboratory test situations is challenging and generally costly and time intensive. In this paper, we describe a novel chamber design that is capable of maintaining low DO levels precisely for a period of at least 4 days with minimal re-adjustment and nitrogen gas requirement. The system is simple, inexpensive and easy to use, and offers the additional benefit of being portable. The utility of this design is demonstrated with an experiment to test the effects of hypoxia and high salinity on hatch rates and yolk-sac larvae survival in the estuarine fish black bream Acanthopagrus butcheri (Munro, 1949). The results show that early life-stage black bream are sensitive to hypoxia and increased salinity, indicating that deterioration in estuarine environmental conditions may have negative effects on spawning success and recruitment to fish populations. This new laboratory technique will be useful for testing future scenarios for the estuaries of southern Australia as predicted by climate change models. Other potential applications and modifications for further development of this new technique are discussed.

Potential predation pressure of littoral mysids on herring ( Clupea harengus membras L.) eggs and yolk-sac larvae

The predation potential of littoral mysid shrimps (Mysidacea) on Baltic herring ( Clupea harengus membras L.) eggs and yolk-sac larvae was studied experimentally. The results showed that littoral mysids feed actively on both eggs and yolk-sac larvae. It was shown that Neomysis integer preys on eggs, which are not attached to the substrate. Alternative food (yolk-sac larvae or zooplankton) did not decrease feeding rate on eggs. Only gravel as a bottom material lowered the ingestion rate to nearly zero. The largest of the mysid species Praunus flexuosus ate yolk-sac larvae more than other mysids and most efficiently. Mysids switched to feed on eggs when larvae and eggs were offered simultaneously, thus predation focused on eggs. It is possible that hydrodynamic signals of moving larvae induced mysids to prey and eggs were easier prey to catch as well as more numerous. In addition egg size is optimal and the nutritive value (measured as C:N ratio) is better compared with larvae. The results indicate that mysids may have local effects on populations of Baltic herring by eating the early life stages, mostly eggs. Especially when large swarms of N. integer shoal in the spawning areas. However, the effect on recruitment of herring is still hard to evaluate.

Early development stages of the red blenny, Parablennius ruber (Teleostei: Blenniidae)

Little is known about the early development stages of Parablennius ruber. In this paper the following stages are described, and illustrations provided for the first time: middle stage egg, late stage egg, yolk-sac larva and preflexion larva. Recently laid eggs were spherical and orange, attached to the substratum in rock crevices. Eggs measured 1.02 mm in diameter. Newly hatched larva measured 4.65 mm total length and had the mouth closed and the anus open, fully pigmented eyes and a big yolk sac. Pectoral fins were present, rounded and not radially pigmented. Yolk was absorbed in 2–3 days at room temperature. Preflexion larvae had pointed pectoral fins, bigger eyes, well developed lips and strong jaws. Operculae were open. Orange chromatophores began to be noticeable between the eyes.

Survival and quality of halibut larvae ( Hippoglossus hippoglossus L.) in intensive farming: Possible impact of the intestinal bacterial community

The high mortality commonly observed during the early life stages of intensively reared halibut ( Hippoglossus hippoglossus L) is believed to be caused by e.g. opportunistic bacteria. However, the impact of particular bacterial species is poorly defined and still remains disputable. The study describes the bacterial diversity in the gastrointestinal tract of halibut larvae in a large number of incubators at a commercial production site. The overall success of larvae was found to be highly variable and analysis of the gut microbiota revealed high variation of the cultivable part as well as the bacterial community of surface sterilised larvae analysed by denaturing gradient gel electrophoresis (DGGE) of PCR amplified 16s rDNA products. Analysis of the bacterial community of unfed yolk sac larvae revealed higher diversity than previously reported, with Marinomonas, Marinobacter, Aeromonas and Shewanella dominating the community structure. There are indications that Marinomonas is found only in the overall most successful first feeding larvae of the period where the Vibrio group dominated the bacterial community together with Shewanella. Vibrio wodanis was identified as a part of the bacterial community of feeding larvae that yielded the poorest overall success of the period. α -Proteobacteria, not previously reported in halibut, were also found as a part of the bacterial community of first feeding larvae. The diverse bacterial community was only partly reflected in the cultivable part which, however, may reflect the dominating bacterial groups of the highly heterogeneous bacterial community of larvae in the production system as a whole. The bacterial community of the Artemia was found to be highly variable in different samples collected through the period. Only a small part of the different groups observed in the bacterial community of surface sterilised larvae was reflected in the cultivable part which was dominated by highly variable groups in different samples of Artemia. Also, the numbers of cultivable bacteria were found to positively correlate with jaw deformation of unfed yolk sac larvae as well as incomplete metamorphosis of feeding larvae.

Diel and seasonal distribution patterns of eggs, embryos and larvae of Twaite shad Alosa fallax fallax (Lacépède, 1803) in a lowland tidal river

The anadromous Twaite shad Alosa fallax fallax (Lacépède, 1803) is globally classified as “Data Deficient” by the IUCN but the Instituto de Conservação da Natureza, Portugal, classified the species as “Vulnerable”. In this study, the aims were to describe the putative diel, seasonal and inter-annual patterns of distribution and abundance of Twaite shad early life-history stages in a lowland tidal river, River Mira (south Portugal), and to examine how changes in temperature, rainfall, microplankton biomass, potential prey and competitors’ predator abundance affect the distribution patterns using generalised additive models (GAM). Twaite shad yolk-sac larvae were collected indiscriminately at various times of day while larvae were more common during daylight hours in comparison to samples collected during the night, independently of tide. Moreover, A. f. fallax eggs, embryos and larvae were found in samples from late-March to mid-June. Peak densities were observed around late-April for eggs, mid-May for embryos and mid to late-May for larvae. The observed among- and within-year changes in abundance of Twaite shad embryos and larvae were related, through GAM, with a combination of environmental covariates, mainly in a non-linear way.

Utilization of free amino acids, yolk protein and lipids in developing eggs and yolk-sac larvae of Japanese eel Anguilla japonica

To elucidate the utilization of major yolk nutrients in eggs and yolk-sac larvae of Japanese eel Anguilla japonica, contents of free amino acids (FAA), 380 kDa lipovitellin (oLv; the major yolk protein in ovulated eggs), and lipids were measured. All larvae hatched by the 2nd day after fertilization at a water temperature of 23 °C, and the hatched larvae absorbed almost all of the yolk mass by the 10th day. The FAA composition in ovulated eggs is unique in that glutamine (Gln) is markedly high (32% of total FAA) in comparison to other pelagic eggs of marine teleosts suggesting the importance of Gln for early development of the Japanese eel. Total FAA content decreased to 45% of the initial level by the 4th day after fertilization. Gln content showed a rapid decrease to 5% of the initial level within 2 days after fertilization. oLv content, measured by enzyme-linked immunosorbent assay using an antiserum against lipovitellin, decreased until the 4th day and was, thereafter, undetected. Total content of triacylglycerol (TG) was stable until the 2nd day, and then decreased until the 8th day. On the other hand, the content of phospholipids (PL) gradually decreased until the end of yolk sac absorption. From these data, we divided the pattern of nutrient utilization in embryos and larvae of Japanese eel into two phases: first, utilization of FAA (especially Gln) and oLv from the 1st day, followed by TG utilization from the 2nd to 4th day by which time more than 30% of the FAA and the oLv stock have been utilized. In addition, PL was utilized as a subsidiary energy source throughout development. Almost all the yolk nutrient were absorbed by the 8th day after fertilization, and it is considered that the larvae need to start feeding before this period.

Rhesus glycoprotein and urea transporter genes are expressed in early stages of development of rainbow trout (Oncorhynchus mykiss)

The objective of this study was to determine if the genes for the putative ammonia transporters, Rhesus glycoproteins (Rh) and the facilitated urea transporter (UT) were expressed during early development of rainbow trout, Oncorhynchus mykiss Walbaum. We predicted that the Rh isoforms Rhbg, Rhcg1 and Rhcg2 would be expressed shortly after fertilization but UT expression would be delayed based on the ontogenic pattern of nitrogen excretion. Embryos were collected 3, 14 and 21 days postfertilization (dpf), whereas yolk sac larvae were sampled at 31 dpf and juveniles at 60 dpf (complete yolk absorption). mRNA levels were quantified using quantitative polymerase chain reaction and expressed relative to the control gene, elongation factor 1alpha. All four genes (Rhbg, Rhcg1, Rhcg2, UT) were detected before hatching (25-30 dpf). As predicted, the mRNA levels of the Rh genes, especially Rhcg2, were relatively high early in embryonic development (14 and 21 dpf), but UT mRNA levels remained low until after hatching (31 and 60 dpf). These findings are consistent with the pattern of nitrogen excretion in early stages of trout development. We propose that early expression of Rh genes is critical for the elimination of potentially toxic ammonia from the encapsulated embryo, whereas retention of the comparatively benign urea molecule until after hatch is less problematic for developing tissues and organ systems.

Intensive larval husbandry and fingerling production of cobia Rachycentron canadum

Methods and results of two larval rearing trials of cobia ( Rachycentron canadum) are presented. These trials were designed to test the efficacy of protocols developed over several years of research in cobia larviculture at the UMEH. The protocols incorporate the use of probiotics and prophylaxis, minimize microalgae use, and include commercially available ingredients for live feed enrichment. During the trials, fertilized eggs were stocked at 400/L and incubated in 1000-L cylinder-conical tanks with flow-through seawater at 500% daily exchange rate. Moderate aeration and pure oxygen were used to maintain dissolved oxygen concentrations above saturation (6.5 mg/L at 26 °C). Hatching occurred at 22–24 h post fertilization. Two day-post-hatch (dph) yolk-sac larvae were stocked in four 12,000-L cylinder-conical tanks at 5 and 10 larvae/L. Beginning on 3 dph, larvae were fed microalgae ( Isochyrsis galbana C-strain) at low concentrations (5–10,000 cell/ml) and enriched rotifers ( Brachionus plicatilis) at 3–5/mL through 9 dph. Beginning on 7 dph, enriched Artemia ( Artemia franciscana GSL Strain) nauplii were fed to larvae at 0.1–1/mL. Cobia larvae were reared at water temperatures ranging from 24.3 to 31.8 °C. Water quality parameters were within normal ranges for seawater: salinity 26–34 ppt, pH 7.92–8.16, and NH 3 < 0.18 mg/L. Vigorous aeration and supplemental oxygen were used at all times during both larval rearing trials to maintain adequate water movement and levels of dissolved oxygen (DO) (7.0–9.0 mg/L). Water was filtered down to 10 μm using standard sand filters filled with broken glass media and bag filters prior to entering the tanks. Daily water exchange rates in the tanks ranged from 100% at 3 dph to 500% from 17 dph onwards. Between 20 and 22 dph, all post-larvae were fully weaned onto dry starting diets. Survival rates of post-larvae measuring 1.5–2.0 cm SL and weighing 0.5 g at 20–22 dph were estimated to be ≥ 50%. Further mortality during the nursery stage to 3–5 cm and 1–3 g fingerlings prior to shipping at 27 dph brought the overall survival rate to an average of 25.7%. Survival rates of fingerlings cultured in tanks initially stocked at lower densities (5 larvae/L) was significantly higher ( P = 0.0078). From 15 dph, post-larvae and fingerlings were daily graded by size with large individuals singled out and stocked into another tank. These trials generated 125,328 fingerlings in four tanks in just two months, levels of production that could sustain a commercial operation and indicate that cobia aquaculture can be viable in the Americas.

Effects of growth rates on the otolith increments deposition rate in capelin larvae ( Mallotus villosus)

Otolith microstructure analysis was applied to known age capelin larvae ( Mallotus villosus) in order to examine the formation of daily increments. In two validation experiments, newly hatched yolk sac larvae were stocked into eight 10 m 3 plastic bags where environmental conditions were kept as natural as possible. The bags were terminated after 35-79 days, the surviving larvae were collected and the otoliths were analysed. Survival in the bags varied between 39 - 71% with average individual length growth rates of 0.25 mm day - 1 . The ages of most larvae were underestimated and the accuracy in age estimation was generally low. Highest accuracy was found for fast growing larvae. On average, the larvae started to form increments about 12 days after hatching, and the increment width increased with age and/or length of the larvae. Larvae showing low body growth rates had fast otolith growth relative to body length.

Use of probiotic bacteria in the rearing of Senegalese sole (Solea senegalensis) larvae

Three candidate probiotics, which had shown antimicrobial activity in vitro against two fish pathogens, were used in the rearing of Senegalese sole larvae and postlarvae. These probiotics improved the survival of starved sole yolk-sac larvae. A feeding experiment of sole larvae and postlarvae comprised three treatments: A, B and C. Cultures of a Vibrio sp. (2J18) were added to treatment A, whereas a gram-positive (J84) and a Shewanella sp. strain (2J27), were added to treatment B, while in a control treatment C no bacteria were added. Addition of bacteria in treatment B increased survival of larvae in the first phase of the experiment [0–20 days after hatching (DAH) (P<0.05)] and decreased the numbers of colony-forming units (CFU) in larval gut 5 DAH compared with the control treatment (P<0.05). No differences were observed in survival (25–47%) during the second phase of the experiment (20–60 DAH). Nevertheless, the total numbers of CFU in fish gut 40 DAH were significantly lower in treatment B (P<0.05). The colonization rates of the added bacteria were the highest 5 and 11 DAH, and the highest average values reached were 65%, 82% and 17% of the total CFU count for the strains 2J18, 2J27 and J84 respectively.

Pelagic eggs and larvae of Coryphaenoides marginatus (Gadiformes: Macrouridae) collected from Suruga Bay, Japan

The pelagic eggs, yolk-sac and pelagic larvae of the macrourid fish, Coryphaenoides marginatus, from Suruga Bay in southern Japan, are described. The identification of the pelagic eggs based on 16S rRNA gene nucleotide sequences agreed with that obtained from morphological analyses. The spherical eggs, 1.14–1.30 mm in diameter, contained a single oil globule 0.30–0.38 mm in diameter, and had hexagonally patterned ornamentation on the chorion, 0.025–0.033 mm in width. Many melanophores were present on the anterodorsal region of the embryo after the caudal end had detached from the yolk. Within a day after hatching, each of the yolk-sac larvae had a body axis that was bent slightly at the anterior trunk region, many dorsal and lateral melanophores on the trunk plus several on the gut, and small irregular wrinkles on the dorsal and anal fin membranes. The pelagic larvae had a short caudal region in comparison to other known congeners (length 2.0–3.2+ times head length vs. 4–7, respectively), a short stalked pectoral fin base, and no elongate first dorsal and pelvic fin rays. They were further characterized by the presence of numerous very dense melanophores from just behind the eye to the anterior part of the caudal region at 5.1 mm head length (25.8+ mm total length). The significant difference in vertical distribution between the pelagic eggs and larvae (dominant depths ca. 200–350 m vs. ca. 10–100 m, respectively), with no subsequent collection of pelagic larvae with greater than 6 mm head length, indicate two stages (rising and falling) of ontogenic vertical migration.

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.

Dietary supplementation of salmon roe phospholipid enhances the growth and survival of Pacific bluefin tuna Thunnus orientalis larvae and juveniles

Previous studies have shown that feeding enriched Artemia induces growth failure in Pacific bluefin tuna (PBT) Thunnus orientalis larvae. This growth failure cannot be improved even if the docosahexaenoic acid (DHA) content in enriched Artemia is elevated to the same level as that in yolk-sac larvae, an ideal live feed for PBT larviculture. This might be caused by the differences in the DHA in the live feeds; i.e., yolk-sac larvae of marine fish have a high level of DHA in the larval phospholipids (PLs) but enriched Artemia store DHA in their neutral lipids (NLs). To test this hypothesis two experiments were conducted to evaluate the effect of dietary PL rich in DHA on growth and survival of PBT larvae (Experiment 1) and juveniles (Experiment 2). Three isoproteic and isolipidic artificial test diets (Diets 1, 2 and 3) and two reference live feeds (Diets 4 and 5) were prepared. Diets 1 and 3 were supplemented with NL and PL fractions of commercial salmon Oncorhynchus gorbuscha roe lipid (SRL) as the lipid source, respectively, whereas Diet 2 was supplemented with a mixture of both lipid fractions. Diets 4 and 5 were enriched Artemia and yolk-sac larvae of Japanese parrot fish Oplegnathus fasciatus, respectively. Diets 1, 3, 4 and 5 were given to PBT larvae for 10 days, whereas Diets 1, 2 and 3 were fed to PBT juveniles for 10 days. In Experiment 1, the growth and survival of PBT larvae fed Diet 3 (high PL fraction) were significantly improved when compared with larvae fed Diets 1 and 4, although the best growth and survival were obtained in larvae fed Diet 5. Similar results were obtained in Experiment 2; i.e., growth and survival were significantly improved in PBT juveniles fed Diets 2 and 3. In both experiments, fish fed Diets 2, 3 and/or 5 had higher total lipid contents, TAG levels, n-3 HUFA and/or DHA levels in NL fraction of the body when compared with fish fed Diets 1 or 4, while such a difference was not observed in the PL fraction. In juveniles over 90% of deaths were caused by collisions with the tank walls and the significant difference in mortality between treatments implies diet also affects behavior. SRL PL is concluded to enhance the growth and survival of PBT larvae and juveniles along with the accumulation of storage lipid and DHA in the body.