Larval Standard Length Research Articles

A Comparative Study on Growth Performance, Body Composition, and Liver Tissue Metabolism Rearing on Soybean Lecithin-Enriched Artemia Nauplii and Microdiet in Rock Bream (Oplegnathus fasciatus) Larvae.

This study is aimed at establishing optimal soybean lecithin (SL) enrichment protocols in Artemia nauplii and at comparing the growth performance, body composition, and liver tissue metabolism in rock bream (Oplegnathus fasciatus) larvae reared on SL-enriched Artemia nauplii or SL-enriched microdiet (MD). The enrichment protocol experiment results indicated 12 h enrichment, and 10 g SL/m3 seawater could obtain desirable results. Rock bream larvae (25 days posthatching (dph)) were fed Artemia nauplii or MD for 30 days with three replicates. At stage 1 (larval 25-40 dph), significantly higher growth performance was observed in larvae fed the live prey (P < 0.05). Conversely, at stage 2 (41-55 dph), feeding with MD significantly increased larval standard length, and specific growth rate compared with those of larvae fed live prey. Larvae fed a MD showed decreased lipolysis-related lipase activity as well as decreased amino acid catabolism-related alanine aminotransferase and aspartate aminotransferase enzyme activities in liver tissue. RNA sequencing revealed that feeding with the MD primarily increased the expression of lipogenesis-related genes and protein translation-related gene expression in the liver tissue. Notably, feeding with MD significantly increased ribosome biogenesis-related genes as well as mitochondria synthesis-related gene expression, indicating a high protein anabolism rate and high energy production in liver tissue. In conclusion, 10 g SL/m3 seawater and 12 h could effectively enrich SL in Artemia nauplii. Retard weaning onto MD led to lower growth performance, which was likely due to the diversity of lipid and protein metabolism.

A flow-through imaging system for automated measurement of ichthyoplankton

Microscopic imaging and morphometric measurement of fish embryos and larvae is essential in environmental monitoring of fish populations and to evaluate larvae development in aquaculture. Traditional microscopy methods require time-consuming, repetitive work by human experts.We present a method for fast imaging and analysis of millimetre-scale ichthyoplankton suspended in seawater. Our system can be easily built from common and off-the-shelf components and uses open-source software for image capture and analysis. Our system obtains images of similar quality to traditional microscopy, and biological measurements comparable to those by human experts, with minimal human interaction. This saves time and effort, while increasing the size of data sets obtained.We demonstrate our approach with cod eggs and larvae, and present results showing biologically relevant endpoints including egg diameter, larval standard length, yolk volume and eye diameter, with comparison to similar measurements reported in the literature.• High throughput, microscope-scale imaging of fish eggs and larvae• Automated measurement of biologically relevant endpoints• Easily built from off-the-shelf components and open-source software

Maternal diet affects utilization of endogenous lipids by red drum Sciaenops ocellatus embryos and early larvae.

Embryonic and early larval development and metabolism of most teleost fishes are fueled entirely by maternally derived nutritional resources (yolk and oil) before the onset of exogenous feeding. The composition of those resources depends, in part, on maternal diet. To examine how diet-induced variations in egg composition affect embryonic and larval utilization of endogenous lipids and fatty acids, we fed red drum (Sciaenops ocellatus) broodstock four different diets to produce distinctive fatty acid compositions in eggs but with no significant difference in total lipid content. We sampled embryos and unfed larvae every 12h from 12h post-fertilization (hpf) until starvation (96-120 hpf; n=5 spawns per diet group). Rates of utilization of the oil globule were significantly different among diet groups, resulting in significant differences in mean oil globule size at the first feeding stage (84 hpf). Utilization rates for 15 fatty acids were significantly different among diet groups and were proportional to their initial concentration. As a result, differences in larval fatty acid compositions among maternal diet groups diminished over time but remained different even at later stages. In addition, larval standard length at 84 hpf was positively correlated with egg total lipid content. This study suggests that the fatty acid composition of yolk and oil affects energy metabolism and tissue composition in red drum larvae. These effects could have consequences for the survival and essential physiological functions of fish larvae during the critical period of transition to exogenous feeding.

MON-712 Restoration of Growth and Fertility in Zebrafish (Danio Rerio) Model with PROP1 Knockout Generated by CRISPR/Cas9 Genomic Editing

Introduction: Hypopituitarism is defined as the deficiency of one or more pituitary hormones and can occur due to pathogenic allelic variants in transcription factors involved in pituitary development. PROP1 gene is responsible for progenitor cell migration from the marginal zone to the anterior lobe, and its terminal differentiation into corticotropes and gonadotropes cell lines besides somatotropes, lactotropes and thyrotropes due to POU1F1 (also known as PIT1) activation. In humans, mutations in the PROP1 gene are the most common cause of congenital hypopituitarism with GH, TSH, LH/FSH, and progressive ACTH deficiencies. A dwarf phenotype with short stature, pituitary hormone deficiency, and infertility has been described in humans and Ames mice lineage harboring mutations in the PROP1/Prop1 gene. Another valuable animal model used in basic research is the zebrafish (Danio rerio) due to a high homology in neuroendocrine functioning. To test the potential of this model, in our previous study, a 32bp insertion carrying a stop codon was directed into the second exon of prop1 with CRISPR/Cas9, establishing a homozygous mutant strain (prop1mut). Objective: To characterize the phenotype and expression patterns of transcription factors and hormones in the zebrafish prop1mut lineage. Methods: prop1, pit1, and gh1 mRNA levels were analyzed during embryonic development at 24 and 72 hours post-fertilization (hpf). RNA from 30 pooled embryos was extracted using DirectZol RNA Miniprep. cDNA was synthesized from 1ug of total RNA using High-Capacity cDNA Reverse Transcription Kit and qPCR was performed using SYBR Green PCR Master Mix. Gene expression was normalized to ef1a and the prop1mut group was compared with the control wild type group (WT). Animals were kept in the tanks at a density of 15 animals/liter and images were acquired at 13 and 20 days post fertilization (dpf) after brief anesthetization using a stereomicroscope and measured in ImageJ software to determine the larval standard length from nose to the end of the spinal cord. Results: At 24 and 72hpf, prop1mut embryos expressed the altered prop1 mRNA at similar levels to the prop1 expression observed in WT. Lower pit1 expression in prop1mut embryos was observed at both periods (p<0.01). Albeit in low levels, similar gh1 expression was observed in both lineages at 24hpf, and prop1mut embryos presented lower gh1 expression at 72hpf (p<0.001). prop1mut larvae presented a significant decrease in size at 13dpf (p<0.001) but not at 20dpf. Conclusion: In this study, the prop1mut zebrafish model exhibited a dwarf phenotype during larval development associated with diminished pit1 and gh1 expression during the embryonic stage. Additionally, in the juvenile stage, the development rate in prop1mut animals was restored, presenting similar standard lengths observed in WT animals.

Intrinsic post-ejaculation sperm ageing does not affect offspring fitness in Atlantic salmon.

Post-meiotic sperm ageing, both before ejaculation and after ejaculation, has been shown to negatively affect offspring fitness by lowering the rate of embryonic development, reducing embryonic viability and decreasing offspring condition. These negative effects are thought to be caused by intrinsic factors such as oxidative stress and ATP depletion or extrinsic factors such as temperature and osmosis. Effects of post-ejaculation sperm ageing on offspring fitness have so far almost exclusively been tested in internal fertilizers. Here, we tested whether intrinsic post-ejaculation sperm ageing affects offspring performance in an external fertilizer, the Atlantic salmon Salmo salar. We performed in vitro fertilizations with a split-clutch design where sperm were subjected to four post-ejaculation ageing treatments. We varied the duration between sperm activation and fertilization while minimizing extrinsic stress factors and tested how this affected offspring fitness. We found no evidence for an effect of our treatments on embryo survival, hatching time, larval standard length, early larval survival or larval growth rate, indicating that intrinsic post-ejaculation sperm ageing may not occur in Atlantic salmon. One reason may be the short life span of salmon sperm after ejaculation. Whether our findings are true in other external fertilizers with extended sperm activity remains to be tested.

Effect of tank colour on foraging capacity, growth and survival of milkfish (Chanos chanos) larvae

Larviculture of milkfish (Chanos chanos) associated with issues like larval deformity, mass mortalities which contribute in variable seed production. Effect of abiotic factors as rearing tank colour and illumination on larvae foraging behaviour, prey localization and ingestion were investigated to improvise milkfish larval rearing system. Reinforced Cement Concrete (RCC) tanks (capacity, 8 t; water salinity, 32 ppt) with three different background colors, white, blue and yellow were divided in five (05) treatment groups with triplicates, i.e. indoor white (T1/C), blue (T2), yellow (T3) color tanks with artificial illumination and semi outdoor blue (T4), yellow (T5) color tanks with solar illumination. Newly hatched milkfish larvae (tl., 3.4 mm) were stocked in the experimental tanks @ 2.5 no l−1 and apart from background colour and source of illumination uniform water quality and feeding regime were maintained in all treatments. Phytoplankton, Chlorella salina @ 103–104 cells ml−1 were maintained from 2 dph to 20 dph; Chlorella grown rotifers, Brachionus plicatilis (enriched with Nannochloropsis oculata paste) were provided @ 20–30 no ml−1 from 3 dph to 14 dph depending on the larval density. Artemia nauplii @ 0.5–1.0 no ml−1 was introduced from 15 dph. At the end of the experiment- 20 dph, highest (p < 0.05) larval survival (45 ± 5.63%) was achieved in tanks providing yellow background colour (T5) compared to control and other treatments. Larval growth (tl., 17.1 ± 1.37 mm) was also found to be highest (p < 0.05) in T5. Increased survival and growth of milkfish in T5 was synchronized with significantly higher (p < 0.05) specific growth rate (SGR), larval gut content relative to other treatments. Milkfish larvae being a day feeder did maximum foraging during 0700 h to 1600 h evident from decreeing prey abundance during that period and as a result positive correlation found between larval standard length and gut content. Larval visibility enhancement in solar illuminated yellow tank act synergistically to perform necessary foraging to acquire nutritional energy for metamorphosis to fry. Above phenomenon may not have occurred in other treatments except T5 and partially in T3. Solar illuminated yellow colour tanks significantly contribute towards mass scale seed production of milkfish.

Spatial variability in post-larval traits of Sicyopterus lagocephalus Pallas 1770 around Reunion Island

The spatial variability of S. lagocephalus post-larval traits, in February 2015, was investigated through comparison of pelagic larval duration (PLD), standard length (SL), body mass (BM) and condition factor among 6 rivers around Reunion Island. The variability of the same traits was also investigated within a recruitment event in another river, in January 2015. Our results showed homogeneity of the PLD both between sites during the recruitment of February 2015, and during the recruitment event of January 2015 at a given site. The other traits were different between the eastern and the western rivers. The post-larvae from the East were characterised by higher BM and condition factor whereas on the West they were longer. These differences can be explained by different environmental conditions experienced by larvae in the coastal oceanic water before they entered the river, but also by different migration routes during their marine dispersal. The coastal water on the eastern side, more turbid and probably trophically richer, could have induced a better growth of the post-larvae compared to those at the same age on the western side. A singularity was highlighted concerning the Marsouins River, located East of the island, where post-larvae were at a more advanced stage of their metamorphosis, characterised by both a smaller size and a lighter weight. This particularity was related to the location of the fishermen trapnet, positioned farther up river compared to all the other rivers, either West or East of the island.

Differentiated stable isotopes signatures between pre- and post-flexion larvae of Atlantic bluefin tuna (Thunnus thynnus) and of its associated tuna species of the Balearic Sea (NW Mediterranean)

The trophic ecology of bluefin tuna larvae (Thunnus thynnus) from the Balearic Sea, together with its co-existing tuna species such as albacore (T. alalunga), bullet (Auxis rochei) and little tunny (Euthynnus alletteratus) were examined by nitrogen and carbon stable isotope analyses. A total of 286 larvae were analyzed for this study, of which 72 larvae corresponded to bluefin, 57 to albacore, 81 to bullet tuna and 76 to little tunny. Tuna larvae were separated into the pre-flexion and post-flexion developmental stages. Within the size 3–9mm standard length (SL), the stable isotope of nitrogen (δ15N) showed significant differences between species where bluefin tuna larvae ranked highest. Pre-flexion bluefin tuna and little tunny larvae showed significantly higher δ15N signatures than the post-flexion larvae. This effect is attributed to a biochemical trace of maternal δ15N signatures. However, neither albacore nor bullet tuna larvae showed this pattern in δ15N signatures, possibly owing to a compensation effect between lower maternal δ15N values transmitted to pre-flexion larvae and the early increase of δ15N values in post-flexion stages. One way ANOVA showed significant differences between species in the stable isotope ratio of carbon (δ13C) values, which suggests specific differences of carbon sources. Furthermore, a similar significant ontogenic effect between δ13C signatures of pre-flexion and post-flexion larvae is also evidenced in all four species. At pre-flexion stages, all species except bullet tuna larvae showed significant negative relationships between δ15N and larval standard length. At post-flexion stages, a significant linear relationship with larval size was only observed in albacore and bullet tuna larvae indicating a possible trophic shift towards early piscivory. With respect to δ13C values with larval size, all four species showed significant linear decreases. It may be explained by the metabolism of growth of somatic mass subject to modification of the relative carbon isotopic sources. In conclusion, the species' signatures of δ15N and δ13C indicate differentiated early life trophic niches. In addition, it is worth remarking the potential use of transgenerational isotopic transmission in future research applications.

Combined effects of elevated pCO2, temperature, and starvation stress on larvae of a large tropical marine fish

Ocean acidification and other environmental changes pose an ecological challenge to marine organisms globally. Although the youngest life stages of these organism are likely to be most affected, a limited number of studies of larval fishes have investigated the effects of combined stressors. We conducted two experiments on larval cobia (Rachycentron canadum) raised under combinations of elevated pCO2 and increased temperature or starvation stress. Larvae responded to individual CO2, temperature, and rationing treatments, and there was a negative effect of elevated pCO2 on starvation resistance, but few synergistic effects of combined stressors. Elevated pCO2 (1700–2100 μatm pCO2) caused a transient but significant reduction in larval standard length (SL), growth rate, and development rate, while warmer temperature (32 vs. 27 °C) caused a consistent increase in SL, development rate, and swimming ability. Larval condition (RNA:DNA ratio) was unaffected by elevated pCO2 although larvae fed a 25% ration had significantly reduced SL, growth rate, and development rate. Under complete feeding cessation, larvae in elevated-pCO2 seawater demonstrated lower starvation resistance, indicating that acidification may increase starvation risk in a patchy marine environment. Overall, our results indicate that larval cobia are resistant to any major direct impact of combined elevated pCO2 and temperature or rationing stress.

Allometric growth and development of organs in ballan wrasse (Labrus bergylta Ascanius, 1767) larvae in relation to different live prey diets and growth rates.

ABSTRACTSmall fish larvae grow allometrically, but little is known about how this growth pattern may be affected by different growth rates and early diet quality. The present study investigates how different growth rates, caused by start-feeding with copepods or rotifers the first 30 days post-hatch (dph), affect allometric growth and development of nine major organs in ballan wrasse (Labrus bergylta) larvae up to experimental end at 60 dph. Feeding with cultivated copepod nauplii led to both increased larval somatic growth and faster development and growth of organ systems than feeding with rotifers. Of the organs studied, the digestive and respiratory organs increased the most in size between 4 and 8 dph, having a daily specific growth rate (SGR) between 30 and 40% in larvae fed copepods compared with 20% or less for rotifer-fed larvae. Muscle growth was prioritised from flexion stage and onwards, with a daily SGR close to 30% between 21 and 33 dph regardless of treatment. All larvae demonstrated a positive linear correlation between larval standard length (SL) and increase in total tissue volume, and no difference in allometric growth pattern was found between the larval treatments. A change from positive allometric to isometric growth was observed at a SL close to 6.0 mm, a sign associated with the start of metamorphosis. This was also where the larvae reached postflexion stage, and was accompanied by a change in growth pattern for most of the major organ systems. The first sign of a developing hepatopancreas was, however, first observed in the largest larva (17.4 mm SL, 55 dph), indicating that the metamorphosis in ballan wrasse is a gradual process lasting from 6.0 to at least 15-17 mm SL.

Trans-intestinal absorption rates differ between free amino acids during larval development in Atlantic herring (Clupea harengus)

Trans-intestinal absorption (TIA) rates for the free amino acids (FAA) alanine, proline, and glutamic acid were measured in two developmental phases of Atlantic herring larvae: Early (14–16day-post-hatch) and Late (37–39day-post-hatch). TIA rates were determined by measuring net uptake of a 14C-radiolabeled FAA tracer solution into the body after administration of a single bolus to the digestive tract by tube-feeding. Tracer solutions (concentration range: 0.02 to 100mM) were administered at <50% of gut volume (GV) and the response of TIA rate to increasing administered dose (pmol FAA ind−1) determined. GV was determined as the maximum volume of a tube-fed liquid bolus that could be retained in the digestive tract of a fasted larva without causing any evacuation from the mouth or anus, and was dependent on larval standard length. Our data revealed that alanine, proline and glutamic acid have different TIA rates (pmolmin−1), and results were consistent at both larval stages. At the same administered dose (pmol ind−1), the TIA rate for glutamic acid was only 8–25% of that of alanine and 15–30% of proline in both larval stages. In Early and Late larvae, the dose-dependent increase in proline and glutamic acid uptake was significantly more rapid than for alanine. Hence, alanine was the most rapidly absorbed FAA at low dose, followed by proline and then glutamic acid, but proline became more rapidly absorbed than alanine at the highest doses, in both stages. In conclusion, the study demonstrated that FAA representing neutral, imino and acidic classes, have different rates of absorption. Across a broad range of concentrations, Atlantic herring larvae have a much lower capacity to deliver glutamic acid from the intestinal lumen to body tissues relative to alanine and proline. Statement of relevanceThis paper provides important and quantitative information to understand uptake of different classes of dietary free amino acids in larval stages of fish. We use herring as model since it gives the best combination of size, transparency, robustness, gut morphology for in vivo tube feeding. The data is relevant for formulation of starter diets.

Comer o ser comido: factores que determinan la condición nutricional de larvas de Engraulis anchoita de la población patagónica de la especie

Fil: Diaz, Marina Vera. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentina

Quantitative characteristics of Atlantic halibut (Hippoglossus hippoglossus L.) egg quality throughout the reproductive season

Assessment of egg quality is an important aspect in finfish hatchery management, but guidelines for such assessment are scarce, especially for marine fish production. In the present work, potential indicators of egg and larval quality were measured in 39 batches of eggs of Atlantic halibut (Hippoglossus hippoglossus L.) throughout the reproductive season. The paternal influence on offspring was minimized by using the same cryopreserved semen for all fertilizations; consequently, maternal effects were emphasized. The progression of the spawning season and ovarian fluid parameters, including pH, electrical conductivity (EC), osmolality, and the amount of fluid were registered. The behavior of the broodfish at egg collection was registered and the eggs were analyzed for cortisol content. Fertilization and hatching rates as well as larvae survival were calculated, and larval standard length and myotome height were measured. Furthermore, the occurrence of major types of larval deformities was registered. The myotome height was significantly (P < 0.05) affected by the spawning season progress. Cortisol content in the eggs was decreasing with the progressing spawning season and correlated positively with the occurrence of yolk-sac edema. The ovarian fluid pH and EC were significantly related to fertilization and hatching rates. High fertilization and hatching success was associated with pH greater than 7.9 and EC less than 2.5 mS/cm. Low fertilization rates (<50%) resulted in further low hatchability from such egg batches. Ovarian fluid EC was significantly and positively related to increased occurrence of yolk-sac edema. High quantity of ovarian fluid in egg batches was associated with reduced egg quality in terms of fertilization and hatching rates and occurrence of yolk-sac edema. A cumulative effect of ovarian fluid pH, EC, osmolality, and quantity explained up to 62% of the total variation in fertilization rates. The findings from the present study indicate that parameters measurable at the initial phase of production, in particular ovarian fluid pH and EC, might have a potential for future use as egg quality indicators in hatchery management.

Paternal effects on early life history traits in Northwest Atlantic cod, Gadus morhua

Summary It is important to understand parental effects on early life history of fish as manifested, for example, in individual fitness of offspring. Immediately after fertilization, parental contributions (both genetic and non-genetic) to embryos will affect larval ontogeny, physiology, morphology and survival. In marine fish, rates of natural mortality are highest during early life and are negatively correlated with rates of growth and body size. In these early life stages (eggs, larvae, young juveniles) subtle differences in mortality can cause large differences in recruitment and year-class success. Therefore, it is particularly critical to understand factors that contribute to variability in mortality during early life. This study focuses on evaluating the potential influence of paternity on rates of mortality and development in eggs and larvae of Northwest Atlantic cod, Gadus morhua. To accomplish this 12 males and two females were crossed using a full-factorial breeding design. Paternity had a strong influence on fertilization success, hatching success, cumulative embryonic mortality, larval standard length, eye diameter, yolk-sac area, and cumulative larval mortality. Female 1 showed an overall ‘weaker’ performance of offspring than Female 2, indicating that deviances can stem from differences in female quality. Nevertheless, paternal contributions to embryonic and larval development were still evident despite differences in female quality, showing that sire effects on offspring are undeniable and can serve as important sources of variation during early life stages in fishes. Overall, these findings have implications for furthering the understanding of recruitment variability and can be used to optimize reproductive output for the aquaculture industry. In addition, the data suggests that the choice of mate during spawning can play a large role in offspring fitness.

Influence of salinity on embryogenesis, survival, growth and oxygen consumption in embryos and yolk-sac larvae of the Nile tilapia

The Nile tilapia is a euryhaline species that offers considerable potential for culture in low-salinity waters. In order to investigate the ability of this species to be reared during the hatchery stages in brackish water, the effects of varying low salinities (0, 7.5, 15, 20 and 25ppt) on hatchability, survival, growth and energetic parameters until yolk-sac absorption were assessed. Salinity up to 20ppt was tolerable, although reduced hatching rates at 15 and 20ppt suggest that these salinities may be less than optimal. Optimum timing of transfer of eggs from freshwater to elevated salinities was 3–4h post-fertilisation, following manual stripping and fertilisation of eggs, however increasing incubation salinity lengthened the time taken to hatch. Dry body weight was related to salinity, with larvae in salinities greater than 15ppt displaying, at hatch, a significantly (GLM: ρ<0.05) lower body weight but containing greater yolk reserves than those in freshwater or lower salinities. Survival at yolk-sac absorption displayed a significant (GLM; ρ<0.05) inverse relationship with increasing salinity and mortalities were particularly heavy in the higher salinities of 15, 20 and 25ppt. Mortalities occurred primarily during early yolk-sac development yet stabilised from day 5 post-hatch onwards. Salinity had a negative effect on yolk absorption efficiency (YAE). Salinity-related differences in oxygen consumption rates were not detectable until day 3 post-hatch. Oxygen consumption rates of larvae in freshwater between 3 and 6days post-hatch were always significantly higher (GLM: ρ<0.05) than those in 7.5, 15, 20 and 25ppt, however, on day 9 post-hatch this pattern was reversed and freshwater larvae had a significantly lower QO2 than those in elevated salinities. Salinity had a significant inverse effect on larval standard length, with elevated salinities producing shorter larvae from hatch until day 6 post-hatch, after which time there was no significant differences between treatments. Salinity had a significant effect on whole larval dry weight, with heavier larvae in elevated salinities throughout the yolk-sac period (GLM; ρ<0.05).

Size‐dependent reproductive success of wild zebrafish Danio rerio in the laboratory

Size-dependent reproductive success of wild zebrafish Danio rerio was studied under controlled conditions in the laboratory to further understand the influence of spawner body size on reproductive output and egg and larval traits. Three different spawner size categories attained by size-selective harvesting of the F(1)-offspring of wild D. rerio were established and their reproductive performance compared during a 5 day period. As to be expected, large females spawned more frequently and had significantly greater clutch sizes than small females. Contrary to expectations, small females produced larger eggs when measured as egg diameter with similar amounts of yolk compared to eggs spawned by large spawners. Eggs from small fish, however, suffered from higher egg mortality than the eggs of large individuals. Embryos from small-sized spawners also hatched later than offspring from eggs laid by large females. Larval standard length (L(S))-at-hatch did not differ between the size categories, but the offspring of the large fish had significantly larger area-at-hatch and greater yolk-sac volume indicating better condition. Offspring growth rates were generally similar between offspring from all size categories, but they were significantly higher for offspring spawned by small females in terms of L(S) between days 60 and 90 post-fertilization. Despite temporarily higher growth rates among the small fish offspring, the smaller energy reserves at hatching translated into lower condition later in ontogeny. It appeared that the influence of spawner body size on egg and larval traits was relatively pronounced early in development and seemed to remain in terms of condition, but not in growth, after the onset of exogenous feeding. Further studies are needed to explore the mechanisms behind the differences in offspring quality between large- and small-sized spawners by disentangling size-dependent maternal and paternal effects on reproductive variables in D. rerio.

The influence of different salinity conditions on egg buoyancy and development and yolk sac larval survival and morphometric traits of Baltic Sea sprat (&lt;i&gt;Sprattus sprattus balticus&lt;/i&gt; Schneider)

The small pelagic sprat (Sprattus sprattus) is a key ecologic player in the Baltic Sea. However, there is long-term variability in recruitment which is thought to be influenced by fluctuations in abiotic and biotic conditions experienced during the early life stages. This study concentrates on the influence of different ambient salinities on sprat egg development, egg buoyancy and survival as well as early yolk sac larval morphometric traits. Egg buoyancy significantly decreased with increasing salinity experienced during fertilization and/or incubation experiments. Field egg buoyancy measurements in 2007 and 2008 exhibited annual and seasonal differences in specific gravity, potentially associated with changes in adult sprat vertical distribution. Neither egg development time nor the duration of the yolk sac phase differed among salinity treatments. At eye pigmentation, larval standard length exhibited high variance among individuals but did not differ among treatments. The largest ecological impact of salinity experienced during spawning was the modification the buoyancy of eggs and yolk sac larvae, which determines their vertical habitat in the Baltic Sea. There are strong thermo- and oxyclines in the Baltic Sea, and thus salinity can indirectly impact

Effects of cyanobacterial extracts containing anatoxin-a and of pure anatoxin-a on early developmental stages of carp

This study compares the effects of pure anatoxin-a and cyanobacterial extracts of an anatoxin-a producing strain on early stages of development of carp. Carp eggs were exposed from 2:30 h to 4 days post-fertilization to different ecologically relevant concentrations of anatoxin-a, provided as pure toxin or contained in the cyanobacterial extracts. Data on time to mortality, mortality rate, time to hatching, hatching rate, skeletal malformations rate, and larval standard length were registered until 8 days post-fertilization. At any tested concentration of anatoxin-a, the pure toxin was almost harmless to carp early stages of development, contrarily to cell extracts that were highly toxic. Only an adverse effect on the larval length was found at the highest concentration of pure toxin, while increasing concentrations of cell extracts caused increasing adverse effects in all the analyzed parameters. Anatoxin-a producing cyanobacteria should be regarded as putative modulators of aquatic ecosystems communities.

Cell cycle analysis of brain cells as a growth index in larval cod at different feeding conditions and temperatures

The percentage of cells dividing in a specific tissue of individual larvae can be estimated by analyzing DNA per cell by flow cytometry. An experimental test was carried out with cod (Gadus morhua) larvae, with brain as the target tissue, to validate this technique as an appropriate growth index for larval fish. Standard length (SL), myotome height, and %S-phase (% of cells in the S-phase of the cell-division cycle) variability were analyzed, with temperature (6 and 10°C), food level (high- and no-food) and larval developmental stage (first feeding, pre-metamorphosis and post-metamorphosis) as independent factors. Cod larvae grew faster (in SL) and presented a higher %S-phase under high-food conditions. Larval SL increased with temperature in rearing and experimental tanks. However, there was a significant interaction between temperature and food in the %S-phase. There were no significant differences in the %S-phase between 6 and 10°C at high-food levels. We suggest that this result is a consequence of temperature-dependency of the duration of the cell cycle. In the absence of food, larvae at 10oC had a lower %S-phase than larvae at 6°C, which may be related to increased metabolic costs with increasing temperature. Considering the effect of temperature, the mean % S-phase explained 74% of the variability in the estimated standard growth rate.

Diet of larval albacore &lt;i&gt;Thunnus alalunga&lt;/i&gt; (Bonnaterre, 1788) off Mallorca Island (NW Mediterranean)

These are the first data on the feeding of larval albacore (Thunnus alalunga Bonnaterre, 1788) in the Mediterranean. Specimens were gathered from day-time bongo-hauls conducted over the SW Mallorcan (Balearic Islands) shelf-slope. Ninety eight percent of 101 individuals ranging from 2.65 to 9.4 mm standard length (SL) contained 1 to 15 prey items per gut. Mean number of prey/gut was 3.55 ± 2.19 (SD). A positive correlation was found between larval SL and the number of prey/gut. The analysis of frequency of occurrence (F), numerical frequency (N), weight frequency (W) and the Index of Relative Importance (IRI) showed a dominance of copepodites and nauplii in the smallest size-class. As larvae grew, cladocerans and Calanoida copepodites dominated the diet, and cladocerans and copepodites were important in F, N and W. Piscivory was observed after notochord flexion and was important in terms of W. A positive correlation between mean prey size and both SL and lower jaw length (LJL) was observed. The niche breadth (S) did not vary with LJL, but the raw prey size range did. Larger copepodites, the absence of nauplii and the incorporation of fish larvae and a larger number of cladocerans in the diet accounted for the increase in mean prey size through increased larval size.