First-feeding Larvae Research Articles

Effect of Food Amounts on Larval Performance, Bacteriome and Molecular Immunologic Development during First-Feeding Culture of European Eel.

Production of European eel offspring has become a reality, but liquid diets during larval culture hold new challenges. This study focused on increasing food amounts without compromising well-being or healthy larvae-bacteria interactions. First-feeding larvae were fed two food amounts (Low = 0.5 mL food/L water vs. High = 1.5 mL food/L water) until 30 days post-hatch (dph). Results indicated that ~75% of larvae ingested the diet in both treatments, but upregulation of a stress/repair-related gene (hsp90) on 25 and 30 dph indicated nutritional inadequacy. Larvae fed a High amount of food were 3.68% bigger, while larvae in the Low-food group showed 45.2% lower gut fullness and upregulated expression of the gene encoding the "hunger hormone" ghrelin (ghrl), indicating signs of starvation. The High-food group larvae exhibited a healthier bacteriome with a higher abundance of potentially beneficial orders (Lactobacillales and Bacillales), whereas the Low-food group showed more potentially harmful orders (Vibrionales, Rhodobacterales, and Alteromonadales). While survival was initially lower in the High-food group, both treatments had comparable survival by the end of the experiment. In conclusion, feeding European eel larvae with High food amounts seemed beneficial, supported by increased gut fullness, reduced ghrl expression (no starvation), enhanced growth, and the presence of a healthier bacteriome.

Benchmarking of early ontogeny parameters as predictors of the first-feeding larvae vitality in spotted rose snapper Lutjanus guttatus

A common problem in marine fish hatcheries is the lack of functional embryonic parameters reliably predicting favorable larval outcomes. Embryos characterized as high-quality by typical assessment methods frequently result in weak larvae with high mortality during the endo-exotrophic transition. Thus, because there is no universal consensus on what parameters are most associated with successful larval survivability, this study aims to determine the most reliable, practical, and real-time predictor of vitality at the earliest developmental stage for first-feeding larvae of L. guttatus. From 18 mass volitional spawnings, the reproductive performance and quality of embryos and larvae were assessed by following quality parameters: total fecundity per spawning, percentage of floating eggs, fertilization rate, blastomere morphology score (at 8–32 cell stages), egg and oil globule volumes, coefficient of variation of eggs and oil globule diameters, percentage of poly-globular eggs, oil globule-to-egg volume percentage, morphological appearance and survival rates at 24 (hatching), 48 and 72 h post-spawning, larvae transition rate, and survival activity index (SAI). SAI was used as a larval vitality benchmark to determine the predictive capacity of the abovementioned parameters. Our results show that blastomere morphology score was the only parameter positively correlated with SAI. However, when examining each component of blastomere morphology to SAI prediction, only the presence of cell inclusions, but not size, symmetry, margins, or adhesions of blastomeres, predict the SAI. This reveals that embryos with defective blastomeres can develop into normal-appearing larvae but are weak to starvation. Therefore, cell inclusions are the best real-time, early, reliable, and functional predictor of first-feeding larvae vitality in L. guttatus.

Maternal spawning experience and thermal effects on offspring viability of chub mackerel and their influence on reproductive success

Maternal effects on offspring viability significantly contribute to the productivity and resilience of exploited marine fish populations. The temporal trend of biomass of chub mackerel (Scomber japonicus) in the western North Pacific showed cyclic fluctuation patterns, but it has been rapidly increasing since 2011. Although there are several assumptions regarding the mechanisms of the population dynamics of this species in these waters, there is a contradiction in the effects of thermal environmental conditions on recruitment success. We explored the effects of maternal age and/or previous spawning experience on egg and offspring traits of captive chub mackerel in response to thermal conditions. Moreover, from the relationship between the growth rate and temperature experienced by captive fish, the experienced temperatures of wild specimens were assessed. The sizes of eggs spawned from females aged 1–3 years were negatively correlated with temperature, but the effects of maternal age on egg size and nutrition were significant with larger and nutrient-rich eggs spawned from 2- or 3-year-old females (repeat spawners) than those from 1-year-old females (first-time spawners) at a given temperature. Such temperature- and maternal-age-dependent egg traits reflected the standard length of first-feeding larvae. The effects of maternal age on the starvation tolerance of larvae after hatching and body sizes of first-feeding larvae were also evident in larvae derived from 3-year-old females showing longer starvation tolerance and larger body heights than those from 1-year-old females. Further, larvae derived from 3-year-old females grew significantly faster than those from 1-year-old females at the tested temperatures. The process of ontogenetic development and growth rate of captive specimens until age 25 days were positively correlated with temperature. Meanwhile, the estimated temperatures experienced by wild specimens until age 25 days ranged from 18.0 to 20.3°C. These findings suggested that there were opposing thermal responses between maternal and offspring traits of chub mackerel, but the temperatures experienced by the main recruit fish may be restricted within the range of temperatures available for spawning. We discuss the mechanisms of reproductive success of this species in accordance with the maternal spawning experience and thermal effects on life history traits.

Possible influence of typhoons, volcanic ash, and ocean productivity on early larval survival and Japanese eel annual cohort recruitment

Northern hemisphere anguillid eel populations declined after continental habitat losses and ocean-atmosphere regime shifts occurred, but the exact causes of declines or recruitment fluctuations remain uncertain. Recruitment variations have been hypothesized to result from variable early larval survival, which could be related to phytoplankton blooms caused by typhoons, because leptocephali feed on productivity-related marine snow. We investigated typhoon occurrences in the Japanese eel early larval growth zone in the western North Pacific relative to Taiwan and Japan glass eel recruitment, sea surface temperature (SST), and Chl-a (2003–2017). Recruitment to the 2 areas was significantly correlated, but was not correlated with general typhoon parameters (wind speed, duration, storm radius) or the number of typhoons each year. The highest (2005, 13 typhoons) and lowest (2012, 14 typhoons) recruitment years had very different storm tracks, and SST and Chl-a anomalies were higher in 2005. Larval transport modelling showed regions where larvae were transported in 2005 in relation to typhoon tracks, and 2005 was unique for having 6 April–August typhoons/storms that affected areas with larvae compared to all other study years (194 total typhoons). Storm-induced phytoplankton blooms and species composition shifts (e.g., diatom increases) are temporary and likely need to occur just before new moon to affect the most vulnerable first-feeding larvae (spawning only occurs near new moons). Typhoon Nesat passed near the spawning area ∼6 days before new moon in June 2005, just before the first-ever caught Japanese eel preleptocephali were collected, and there were 2 well-timed-placed August typhoons. The largest-ever eruption of the Anatahan Volcano north of Guam (eruptions 2003–2008) appeared to deposit potentially iron-rich ash (can cause blooms) into the region before new moon in April 2005, which might have increased April-spawned larval survival. Increased early larval survival could have occurred in 3-of-5 new moon spawning periods in 2005, and ash could also have increased productivity, which might have increased recruitment. Further research is needed to examine if marine snow composition and early larval survival may influence anguillid eel recruitment.

Trade-offs between risks of predation and starvation in larvae make the shelf break an optimal spawning location for Atlantic bluefin tuna.

Atlantic bluefin tuna (ABT) (Thunnus thynnus) travel long distances to spawn in oligotrophic regions of the Gulf of Mexico (GoM) which suggests these regions offer some unique benefit to offspring survival. To better understand how larval survival varies within the GoM a spatially explicit, Lagrangian, individual-based model was developed that simulates dispersal and mortality of ABT early life stages within realistic predator and prey fields during the spawning periods from 1993 to 2012. The model estimates that starvation is the largest cumulative source of mortality associated with an early critical period. However, elevated predation on older larvae is identified as the main factor limiting survival to late postflexion. As a result, first-feeding larvae have higher survival on the shelf where food is abundant, whereas older larvae have higher survival in the open ocean with fewer predators, making the shelf break an optimal spawning area. The modeling framework developed in this study explicitly simulates both physical and biological factors that impact larval survival and hence could be used to support ecosystem based management efforts for ABT under current and future climate conditions.

Maturation of the digestive system of Downs herring larvae (Clupea harengus, Linnaeus, 1758): identification of critical periods through ontogeny

Digestive system functionality is a key process linked to larval recruitment and survival. However, little is known about organ development and enzyme maturation of the digestive system of North Sea Atlantic herring (Clupea harengus). In this study, herring larvae were reared at 13 °C from hatching to 69 day post hatch, covering four developmental stages: (1) yolk sac (8–9 mm), (2) pre-flexion (9–14 mm), (3) flexion (12–18 mm) and (4) post-flexion stages (15–30 mm). Combined histological (semi-quantitative scoring) and enzyme analyses (pancreatic and intestinal) showed that developmental stages are strongly linked to physiological changes. The larvae lack a functional stomach and use the intestine as the primary site of digestion which is mainly supported by pancreatic enzyme activity. The intestine acquired adult enzymatic digestive features with a functional brush border at the end of the flexion stage and pyloric ceca started to develop during the post-flexion stage. The transition from pre-flexion to flexion stage and the end of the post-flexion stage are energetically taxing periods as indicated by a reduced number and size of liver vacuoles. Based on these findings, we consider these moments as critical periods, where herring larvae could be dramatically affected by suboptimal feeding conditions in the field. This implies that pre-flexion stage larvae with low or no liver reserves may not be able to proceed to the next developmental stage. Hence, the level of energy storage in first-feeding larvae needs to be examined for its use as a field indicator of survival and development.

An Endeavor to Find Starter Feed Alternatives and Techniques for Zebrafish First-Feeding Larvae: The Effects on Viability, Morphometric Traits, Digestive Enzymes, and Expression of Growth-Related Genes.

Low and variable growth and survival rates (SR) of 6-10 days postfertilization zebrafish larvae are a problem. This problem seems to be linked to starter feed characteristics. This study is an attempt to find alternatives to address these requests. For this, larvae were fed fresh and lyophilized microalgae (Chlorella, Scenedesmus, and Haematococcus), egg yolk (YOLK), lyophilized Artemia nauplii (LAN), and a combination of them. The lowest SR was observed in algae-fed larvae. All died on day 11 showing an emaciated appearance, similar to starved larvae. The highest SR was observed in YOLK- and LAN-fed larvae, which also showed an elongated anterior part of the body. Negative correlations of SR with vegfaa (vascular endothelial growth factor) and morphometric traits with igf2a (insulin-like growth factor) were also found and supported by changes at the molecular level. The presence of algae in the digestive tract of the larvae and the observation of fecal droppings indicate that the algae have an appropriate size and are palatable. The increase in the digestive enzyme activity shows the larval effort to digest the algae. The fact that the algae-fed larvae died even before the larvae were kept in starvation indicates the dramatic amount of energy that the larvae spent in microalgae digestion. Although both YOLK- and LAN-fed larvae had the highest SR, LAN group started to feed on Artemia nauplii sooner. This can be linked to the delayed growth in YOLK-fed larvae and an accelerated growth in the case of LAN-fed group. LAN is an expensive feed with negative effects on water quality, whereas YOLK is a cheap and nutritionally balanced feed with fine granular texture that contributes to a larval SR similar to LAN without affecting water quality. In conclusion, microalgae cannot be considered a suitable starter food for zebrafish, whereas LAN and YOLK can be considered good starter feeds.

Influences of claywater and greenwater on the skin microbiome of cultured larval sablefish (Anoplopoma fimbria)

BackgroundThe skin microbiome of marine fish is thought to come from bacteria in the surrounding water during the larval stages, although it is not clear how different water conditions affect the microbial communities in the water and, in turn, the composition and development of the larval skin microbiome. In aquaculture, water conditions are especially important; claywater and greenwater are often used in larval rearing tanks to increase water turbidity. Here, we explored the effects of these water additives on microbial communities in rearing water and on the skin of first-feeding sablefish larvae using 16S rRNA gene sequencing. We evaluated three treatments: greenwater, claywater, and greenwater with a switch to claywater after 1 week.ResultsWe observed additive-specific effects on rearing water microbial communities that coincided with the addition of larvae and rotifer feed to the tanks, such as an increase in Vibrionaceae in greenwater tanks. Additionally, microbial communities from experimental tank water, especially those in claywater, began to resemble larval skin microbiomes by the end of the experiment. The differential effects of the additives on larval sablefish skin microbiomes were largest during the first week, post-first feed. Bacteria associated with greenwater, including Vibrionaceae and Pseudoalteromonas spp., were found on larval skin a week after the switch to claywater. In addition to additive-specific effects, larval skin microbiomes also retained bacterial families likely acquired from their hatchery silos.ConclusionsOur results suggest that larval sablefish skin microbiomes are most sensitive to the surrounding seawater up to 1 week following the yolk-sac stage and that claywater substituted for greenwater after 1 week post-first feed does not significantly impact skin-associated microbial communities. However, the larval skin microbiome changes over time under all experimental conditions. Furthermore, our findings suggest a potential two-way interaction between microbial communities on the host and the surrounding environment. To our knowledge, this is one of the few studies to suggest that fish might influence the microbial community of the seawater.

Lipid content and fatty acid dynamics of female muscle, oocytes and larvae of Prochilodus argenteus (Spix & Agassiz, 1829)

This work aimed to determine fatty acid dynamics and lipid composition of female muscle, oocytes, newly hatched larvae (NHL) and first feeding larvae (FFL) of Prochilodus argenteus. Oocytes and NHL had the highest percentages of total lipids. Neutral lipids (NL) and polar lipids (PL) remained constant from oocytes through the larval stages (P < 0.05). Among NL, C18:2n 6 had its highest percentage in muscle (P < 0.05) and C18:3n 3 in muscle and oocytes. The highest percentages of arachidonic acid (AA) were in muscle and FFL. The highest percentages of n-9 and n-6 series were in muscle. The highest values of n-3HUFA were in the larval stages while the highest of n-6HUFA were in muscle and FFL. Percentage of ∑SFA in LN was highest in oocytes, NHL and FFL (P < 0.05) while ∑MUFA was highest in muscle, oocytes and NHL. The highest percentages of ∑PUFA were in muscle and FFL. For PL, however, C18:2n 6 and AA were highest in muscle (P < 0.05) while eicosapentaenoic acid was highest in muscle and oocytes. Percentage of ∑SFA in LP was highest in NHL and lowest in FFL and muscle. The highest percentage of ∑MUFA was in oocytes, NHL and FFL (P < 0.05). The highest percentages for series n-9 were in oocytes and FFL (P < 0.05), while the highest percentages for series n-6 were in muscle and oocytes. The lowest percentage for n-6HUFA was in NHL. The n-3 fatty acids were incorporated into the yolk from body reserves, which were stored prior to vitellogenesis and mobilized to the oocytes. The increase in docosahexaenoic acid reflects the ability of the species to lengthen and desaturate C18:3n 3 yielding n-3HUFA, thus demonstrating the importance of this fatty acid during early development.

Influence of food concentration and abiotic parameters on population density growth of the ciliated marine protozoan Euplotes sp. under controlled conditions

High mortality is common when culturing most marine fish larvae, especially during the transition from endogenous to exogenous feeding. In aquaculture, many species of marine fish are not able to survive when only fed enriched rotifers and Artemia spp. nauplii. Ciliates are a potential alternative live food organism for first-feeding larvae, because they can grow to high population densities, accept inert diets, and are natural prey organisms of marine fish larvae. The range of culture parameters to optimize population growth of the ciliate Euplotes sp. are unknown. Five experiments were conducted to determine the effects of food concentration and abiotic factors including salinity, aeration rate, temperature and photoperiod on population growth of the ciliate Euplotes sp. Results indicated the optimal ranges for population growth of Euplotes sp. was a temperature between 26 and 32°C, salinities from 20 and 35 g/L, food (Protein Selco®) concentrations of 250 and 500 mg/million ciliates, absence of or low aeration (8.5 cm3/min) and the photoperiod 0L:24D. Euplotes sp. can tolerate high ammonia and very low dissolved oxygen concentrations, and population growth can occur in these conditions for at least 7 days.

Acute Toxicity of Salt Cavern Brine on Early Life Stages of Striped Bass (Morone saxatilis).

A plan to create solution-mined salt caverns for natural gas storage by discharging brine into the Shubenacadie River estuary poses a potential risk to an "endangered" stock of striped bass. Toxicity of brine made from both salt-core and artificial sea-salt "Instant Ocean" was assessed by 1-h acute toxicity tests at both 19°C and 12°C, the typical thermal range in June, post-spawning. The short test duration was justified given the rapid dilution of the brine in the macrotidal estuary. The median lethal concentration (LC50 1h) 95% confidence intervals of salt-core brine at 19°C for eggs was 51-60 parts per thousand (ppt); yolk-sac larvae 34-55ppt; first-feeding stage larvae (6-8mm total length, TL) 37-44ppt, and 30-46ppt for large larvae (14-20mm TL). Among juveniles, the median lethal concentration was significantly higher compared to larvae: 51-58ppt for early juveniles (4-cm fork length, FL) and 63-67ppt for juveniles 12-cm FL. The toxicity of brine made from either Instant Ocean or salt-core was similar. At 12°C, yolk-sac larvae salinity tolerance was 30% lower than at 19°C, whereas other life stages exhibited a similar response to 12°C and 19°C. The threshold observed effect concentration (TOEC) of the salt-core ranged from 24.4ppt on large larvae to 59.7ppt on 12-cm juveniles. In conclusion, a very low direct threat to striped bass is estimated for the discharge of brine into the Shubenacadie River estuary.

Embryonic development of the bullseye puffer Sphoeroides annulatus (Tetraodontidae): A morphofunctional approach to ontogenetic steps.

The embryonic development of the bullseye puffer, Sphoeroides annulatus, was characterized on the basis of the theory of saltatory ontogeny. This theory predicts a correlative relationship between the ontogeny-type in an altricial-precocial spectrum and the habitat that a species occupies within an unstable-stable environmental spectrum. Because S. annulatus inhabits a variety of unstable environments along a wide latitudinal range, the hypothesis that this species presents one of the most altricial embryonic developments among tetraodontids was tested. Based on major developmental events that marked the ontogenetic thresholds nine embryonic steps were identified. Developmental features such as small adhesives eggs, lack of vitelline circulation, small free embryos swimming up at hatching guided by positive phototaxis, and small first-feeding larvae actively swam in the water column, suggest that S. annulatus belongs to the reproductive guild of the nonguarders-lithopelagophils. Moreover, a comparative analysis of the developmental sequences, egg size, and first-feeding larvae size between tetraodontids confirms the hypothesis of this study and supports the evolutionary principle of the altricial-precocial spectrum postulated in the theory of saltatory ontogeny.

Retinal adaptations of southern bluefin tuna larvae: Implications for culture

We examined Southern bluefin tuna, Thunnus maccoyii, larvae to identify specific retinal adaptations that would indicate both important parameters for culture and larval ecology in the wild. Plastic resin histology, microspectrophotometry and behavioural feeding responses were used to describe visual development. Thunnus maccoyii larvae reflected the visual morphogenesis template commonly observed in many other marine fish species exhibiting indirect development. First-feeding (3 days post-hatching, [dph], 3.4 mm standard length [SL]) larvae possessed tightly packed single cone photoreceptors. Rods and twin cones were present in the retina in post-flexion larvae (21 dph, 8.39 mm fork length [FL]) with cone mosaic patterns observed in juveniles (30 dph, 21 mm FL). Based on the spacing of adjacent photoreceptors and focal length, first feeding larvae had a maximum theoretical visual acuity of 1.23 ± 0.11° that decreased to 0.14 ± 0.02° at 30 dph. Thunnus maccoyii displayed high cell density in the ventral retinal region (cones, bipolar and horizontal cells), a low convergence of cone cells to ganglion cells throughout the retina during larval development (1.1 ± 0.2 to 1.4 ± 0.3 at 3 dph and 30 dph, respectively), and early development of retinal pigment epithelium (RPE) migration. Microspectrophotometry showed twin cone visual pigments maximally sensitive to light in the blue-green part of the visual spectrum (wavelength of maximum absorption [λmax] of 494 nm, 507 nm and 524 nm), and behavioural experiments showed they fed preferentially at these wavelengths. Increased retinal cone densities in the ventral region indicated a localized region specialized for acute vision for prey and predator detection in the upward direction (dorsal plane) at an early age, representing a possible adaptation to life in deeper oceanic waters. The apparent high acuity and photopic sensitivity observed in T. maccoyii is hypothesised to be associated with the ability to feed in low light conditions. This has important practical considerations in determining lighting regimes for culture of T. maccoyii and possibly for other tuna species.

Predatory posture and performance in a precocious larval fish targeting evasive copepods.

Predatory fishes avoid detection by prey through a stealthy approach, followed by a rapid and precise fast-start strike. Although many first-feeding fish larvae strike at non-evasive prey using an S-start, the clownfish Amphiprion ocellaris feeds on highly evasive calanoid copepods from a J-shaped position, beginning 1 day post-hatch (dph). We quantified this unique strike posture by observing successful predatory interactions between larval clownfish (1 to 14dph) and three developmental stages of the calanoid copepod Bestiolina similis The J-shaped posture of clownfish became less tightly curled (more L-shaped) during larval development. Larvae were also less tightly curled when targeting adult copepods, which are more evasive than younger copepod stages. Strike performance measured as time to capture and as peak speed improved only slightly with larval age. Therefore, the J-posture may allow first-feeding larvae to minimize disturbance during their approach of sensitive prey, and may represent an alternative predatory strategy to the prototypical S-start.

Effects of climate and demography on reproductive phenology of a harvested marine fish population

Shifts in phenology are a well-documented ecological response to changes in climate, which may or may not be adaptive for a species depending on the climate sensitivity of other ecosystem processes. Furthermore, phenology may be affected by factors in addition to climate, which may accentuate or dampen climate-driven phenological responses. In this study, we investigate how climate and population demographic structure jointly affect spawning phenology of a fish species of major commercial importance: walleye pollock (Gadus chalcogrammus). We use 32years of data from ichthyoplankton surveys to reconstruct timing of pollock reproduction in the Gulf of Alaska and find that the mean date of spawning has varied by over 3weeks throughout the last >3 decades. Climate clearly drives variation in spawn timing, with warmer temperatures leading to an earlier and more protracted spawning period, consistent with expectations of advanced spring phenology under warming. However, the effects of temperature were nonlinear, such that additional warming above a threshold value had no additional effect on phenology. Population demographics were equally as important as temperature: An older and more age-diverse spawning stock tended to spawn earlier and over a longer duration than a younger stock. Our models suggest that demographic shifts associated with sustainable harvest rates could shift the mean spawning date 7days later and shorten the spawning season by 9days relative to an unfished population, independent of thermal conditions. Projections under climate change suggest that spawn timing will become more stable for walleye pollock in the future, but it is unknown what the consequences of this stabilization will be for the synchrony of first-feeding larvae with production of zooplankton prey in spring. With ongoing warming in the world's oceans, knowledge of the mechanisms underlying reproductive phenology can improve our ability to monitor and manage species under changing climate conditions.

Dried Rotifer Sheet: A Novel Live Feed for Rearing First-Feeding Larvae.

Rotifers are now becoming a standard live feed for first-feeding larvae, because of their easy rearing protocol and improved growth and survival rate, compared with other fish feed, paramecia, and processed powder fish feeds. In a group of rotifers, bdelloid rotifer, a freshwater plankton, exerts cryptobiosis (an ametabolic state of life) in response to desiccation and survived for a long time. Here, we created "dried rotifer sheet" for rearing larvae in their early developmental stage. More than 80% rotifers could survive after 18-month desiccation in the filter paper. Larvae fed with the revived rotifer from dried rotifer sheet exhibited the higher survival rate with less pollution of their breeding water, compared with fine-powdered processed feeds or live paramecia. Our new feeding method is suitable for rearing larvae, and enables screening experiments with first-feeding larvae.

Acute hyperosmotic stress test for vigor assessment of first-feeding larvae of spotted sand bass Paralabrax maculatofasciatus and spotted rose snapper Lutjanus guttatus

espanolResumen: En este estudio se investigo la tolerancia de larvas a la primera alimentacion de la cabrilla arenera Paralabrax maculatofasciatus y del pargo flamenco Lutjanus guttatus a un estres hiperosmotico agudo. Embriones de P. maculatofasciatus y L. guttatus fueron incubados en microplacas de 48 celdas a 23 y 28°C, respectivamente. Larvas de primera alimentacion fueron expuestas por triplicado a salinidades de 35 a 95 g L-1 o 35 a 85 g L-1, y la supervivencia fue monitoreada de 0,5 a 3,5 h o 0,5 a 53 h, para P. maculatofasciatus y L. guttatus, respectivamente. Los resultados mostraron que la mortalidad aumento de manera diferente entre los tratamientos desde el primer tiempo de exposicion en cada especie. Salinidades extremas fueron letales en 30 min. Salinidades cercanas al control fueron sub-letales. En salinidades intermedias, la mortalidad se ajusto a un modelo potencial o lineal. Para P. maculatofasciatus, los valores de LC50 obtenidos entre 0,5 y 3,5 h fueron de 73,4 a 65,4 g L-1. Para L. guttatus los valores de LC50 obtenidos entre 2 y 5 h fueron de 57,3 a 54,5 g L-1. La comparacion de LC50 entre especies mostro que las larvas de P. maculatofasciatus tuvieron una mayor tolerancia al estres hiperosmotico. Con base en los resultados obtenidos en cada especie, se recomienda la exposicion a 70 g L-1 por 1 h para P. maculatofasciatus y 57 g L-1 por 2 h para L. guttatus, cuando se realicen pruebas de estres hiperosmotico. Esta prueba de estres es objetiva, sencilla y puede utilizarse tanto en estudios sobre nutricion y manejo de reproductores como en plantas de produccion de juveniles como metodo de control de calidad. EnglishAbstract: This study investigated the tolerance of first-feeding larvae of spotted sand bass Paralabrax maculatofasciatus and spotted rose snapper Lutjanus guttatus to acute hyperosmotic stress. P. maculatofasciatus and L. guttatus embryos were incubated in 48-well microplates at 23 and 28°C, respectively. The first-feeding larvae were exposed in triplicate to salinities of 35 to 95 g L-1 or 35 to 85 g L-1, and survival was monitored from 0.5-3.5 h or 0.5-53 h, for P. maculatofasciatus and L. guttatus, respectively. The results showed that mortality increased differently among treatments from the first exposure time in each species. Extreme salinities were lethal in 30 min. Salinities close to the control were sub lethal. At intermediate salinities, mortality was fitted to a potential or linear model. For P. maculatofasciatus, the LC50 values obtained between 0.5 and 3.5 h were 73.4 to 65.4 g L-1. For L. guttatus the LC50 values obtained between 2 and 5 h were 57.3 to 54.5 g L-1. Comparison of LC50 between species showed that P. maculatofasciatus larvae had a higher tolerance to hyperosmotic stress. Based on the results for each species, it is recommended to expose to 70 g L-1 for 1 h for P. maculatofasciatus and 57 g L-1 for 2 h for L. guttatus when conducting hyperosmotic stress tests. This stress test is objective, simple, and can be used in both studies on broodstock nutrition and management and in hatcheries as a quality control method.

Effects of rearing temperature on growth and survival of larval sablefish (Anoplopoma fimbria)

The effects of three different rearing temperatures (12, 15 and 18°C) on growth and survival of sablefish larvae (Anoplopoma fimbria) were examined from 5 days poststocking to weaned subjuveniles. First-feeding larvae were stocked into 960-L circular tanks at a density of 15 larvae/L (n = 3 per temperature treatment). Feeding, increases in light and water flow and other changes during the experiment were based on a degree-day (°Cday) schedule to adjust for time and temperature. The larvae were weaned on calendar day 41, 34 and 30 in the 12, 15 and 18°C treatments respectively. Survival to weaning was greater at 15 than 12 or 18°C. Calendar day and degree-day length and dry weight were greater in the 18°C treatment. The larvae were weaned 7 days earlier at 15°C and 11 days earlier at 18°C compared to larvae at 12°C. Sablefish larvae can be reared at 15°C with faster growth and good survival compared to 12°C and at an approximately 17% reduction in cost and labour. Sablefish grew even faster but had higher mortality rates at 18°C compared to 15°C. Results from genotyping strongly suggest that there is a genetic basis for performing differentially at varying rearing temperatures and would also suggest that selection for faster growth and higher survival could be accomplished in a broodstock programme.

Expression of long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis genes and utilization of fatty acids during early development in rabbitfish Siganus canaliculatus

Rabbitfish S. canaliculatus is the first marine fish reported to possess long-chain polyunsaturated fatty acids (LC-PUFA) biosynthetic ability, but the initiation of the LC-PUFA biosynthesis in this species is still unknown. In this study, the gene expression of Δ5/Δ6 fatty acid desaturase (Fad), Δ4 Fad and two fatty acid elongases, four key enzymes for LC-PUFA biosynthesis, were measured during the embryonic and unfed larval development of rabbitfish. Correspondingly, the fatty acid composition of rabbitfish embryos was determined. The results showed that DHA was the primary fatty acid utilized at the zygotic stages. The mRNA expression of the four key genes was detected from 8hpf (hours post-fertilization) onwards, with a low level of elovl5 mRNA contrary to the high expression of Δ4 fad mRNA. Subsequently, the elevated expression of Δ5/Δ6 fad and two elongase genes was observed after hatching, and then a great increment in the expression of all four key genes was detected at 3–4dph (days post-hatching). These results indicate the production of DHA from EPA via the “Δ4 Fad” pathway as well as the alternative “Sprecher” pathway at the yolk-sac larval stages. Furthermore, the entire LC-PUFA biosynthetic pathway of converting C18 PUFA precursors to DHA is activated just after the onset of first-feeding. This study provides information on LC-PUFA biosynthesis during early development in rabbitfish, and offers an approach to determine the nutritional requirements of first-feeding larvae for rabbitfish and other marine fish.

Description of the composition of fatty acids and lipids in the breeders muscle, oocytes and in the embryonic development of Brycon orthotaenia (Günther, 1864)

The objective of this work was to evaluate the fatty acid and lipid composition of oocytes, newly hatched larvae (NHL), first feeding larvae (FFL) and muscle tissue of female Brycon orthotaenia broodstock. Total and polar lipid was significantly (P<0.05) abundant in oocytes and larvae in different stages of development. The lowest content (P<0.05) of total lipids was found in the muscles, whereas total lipid content of oocytes, NHL and FFL did not show any significant difference. Polar lipid content was different (P<0.05) between NHL and FFL. For the neutral the lowest values of C18:2n 6 occurred during the initial feeding period, whilst C20:4n 6 (AA) exhibited the highest percentage in FFL (P<0.05). C22:6n 3 (DHA) was highest (P<0.05) in FFL. The neutral lipid n-9 and n-6 was highest in muscle of females. The n-3HUFA was highest in NHL and in FFL, n-6HUFA was highest in FFL (P<0.05). The ratios of DHA/EPA were higher (P<0.05) in oocytes and FFL. In fatty acids of polar lipids, C20:5n 3 (EPA) did not show differences (P>0.05) between stages. C18:3n 3 was highest (P<0.05) in NHL and FFL. C20:4n 6 (AA) and C22:6n 3 (DHA) showed the highest percentages during the larval stages. The fatty acids n-3 series was significantly higher (P<0.05) in FFL. The n-6HUFA was highest during development larval (P<0.05). The increases DHA reflects the ability of the species to elongate and desaturate to obtain n-3HUFA from 18:3n 3, shows the importance of this fatty acid during early development.