Newly-hatched Larvae Research Articles

Neurokinin B in the yellowtail kingfish (Seriola lalandi) and its potential role in controlling reproduction

The neurokinin B (NKB) system acts as a crucial modulator in the regulation of reproduction and feeding in mammals, however limited information is available in teleosts regarding its potential role in reproductive functions. Herein, we have identified its encoding gene, namely tachykinin 3 (tac3), in the yellowtail kingfish. The full-length tac3 cDNA sequence was 372 bp in size and encoded a 123-aa preprohormone, including two mature peptides, NKB and NKF. Tissue distribution analysis showed that tac3 was primarily expressed in the intestine of yellowtail kingfish. During embryonic development, the highest mRNA levels of tac3 were observed at stage 4 (16-cell) and stage 14 (newly-hatched larva). The peak of tac3 transcript levels was also noticed at 30 days post-hatching during early ontogeny. The physiological effects of NKB and NKF on expression of brain and pituitary genes along with plasma hormones levels were further analyzed by intraperitoneal injection. NKB exerted a stimulatory effect on gnrh1, gnrh2, gnih, and kiss2r mRNA levels, but suppressed kiss1r, gnihr, gal, gh, lhβ, and fshβ mRNA levels. An evident increase was observed on transcript levels of gnrh1, gnrh2, kiss1, kiss2, gnih, and gnihr after NKF treatment, whereas kiss1r, kiss2r, gh, lhβ, and fshβ mRNA levels were down-regulated. Moreover, NKF, but not NKB, reduced serum estradiol levels, and both of these two peptides suppressed serum 11-keto testosterone levels. Taken together, our results provide preliminary evidence that the NKB system participates in the control of reproduction in yellowtail kingfish via acting on brain, pituitary and gonadal hormones.

Responses of digestive enzyme profiles in newly-hatched (Zoea I) larvae of the mud crab Scylla serrata to intermittent food availability and food deprivation.

Activities (mU larva-1) of enzymes critical to digestion were examined to better understand how newly-hatched (Zoea I) larvae of the mud crab Scylla serrata respond to intermittent food availability and food deprivation. Specifically, this study examined the activities of trypsin-like proteases, nonspecific esterases, and α-amylase across three experiments that simulated scenarios in which larvae hatch and experience rearing conditions where food was either: (1) continuously available or unavailable; (2) initially unavailable, but subsequently available; or (3) initially available, but subsequently unavailable. Results showed that food availability exerts a significant influence on enzyme profiles in newly-hatched larvae, with nutritional history influencing their response to food deprivation. When food was unavailable from hatch, there was no significant change in larval enzyme activities between 6 and 78h post-hatch. If food became available at any point during this period, however, newly-hatched larvae were capable of rapidly (within 12-24h) adjusting enzyme activities in response. Furthermore, a short (36h) period of food availability appears sufficient to permit continuous substrate utilization during subsequent food deprivation of equivalent duration. Such flexibility is an important physiological strategy allowing newly-hatched larvae of S. serrata to adapt and thrive in challenging tropical oceanic environments and provides a basis for optimizing protocols for hatchery production of this species.

Evaluation of starvation status in the early developmental stages of black rockfish (Sebastes schlegelii) based on morphological and histological characteristics.

Assessing the nutritional status and identifying major causes of mortality in larvae experiencing varying degrees of starvation are crucial for establishing appropriate feeding protocols and enhancing the welfare of hatchery-reared fish. The black rockfish Sebastes schlegelii is an important species in aquaculture and stock enhancement efforts in China, Japan, and Korea. This study aimed to identify optimal diagnostic morphometric indicators of starvation in newly hatched (0-6 days post-hatch, DPH) and postlarval stages (27-37 DPH) of this valuable fish species through histological analyses. Our findings revealed that certain morphometric parameters, including body length, the ratios of eye diameter to head height, body height to body length, and abdomen height to body height, exhibit sensitivity to starvation during both larval and postlarval stages. Particularly, the ratios of body height to body length and abdomen height to body height emerged as the most sensitive morphometric indicators of starvation. Histological examinations of the digestive system revealed rapid alterations in the morphology of hepatic parenchymal cells, accompanied by a significant decrease in the number of lipid cells in the liver during episodes of food deprivation. Starvation induced cellular degeneration in the digestive organs, manifested by reduced heights of epithelial cells and mucosal layers in the intestine, oesophagus, and stomach, along with degeneration and separation of muscle fibers. Among these variables, the height of the intestinal submucosa and muscle layer emerged as the most sensitive indicators reflecting nutritional conditions in newly hatched larvae. In contrast, the height of intestinal striated borders and mucosal folds proved to be the most sensitive indicators in the postlarval stage. Furthermore, the height of intestinal epithelial cells and the number of lipid vacuoles in enterocytes exhibited high sensitivity to food deprivation in both newly hatched larvae and postlarvae. These findings underscore the varying resilience of fish to starvation during different developmental phases and highlight the utility of morphological sensitivity characteristics as reliable diagnostic indices for assessing nutritional status in relation to starvation or suboptimal feeding during the early developmental stages of black rockfish in hatchery-reared processes.

The behaviour of recently-hatched caddis larvae from temporary water bodies in the British Isles

Caddisflies use four basic methods to ensure that newly-hatched larvae become aquatic insects. One is to lay the eggs underwater so larvae can start a free life immediately after hatching. Another method is to lay the eggs above water and the hatched larvae fall or wriggle into the water. Caddisflies from waters that dry out in summer often have a female diapause gradually becoming sexually mature and often do not lay their clutches until late summer or autumn, when rising water levels flood the eggs. The hatched larvae develop into pupae by March-May, from which adult caddisflies hatch again emergence beginning in spring. Some caddisflies from waters that dry out lay in summer and those eggs hatch soon after laying so it is as a larva that they survive the dry period.

Amino acid and fatty acid compositions of various stages of Chanos chanos larvae: Implications for larval feed formulation

Amino acid (AA) and fatty acid (FA) composition of the fertilised eggs and different larval stages (at 0, 3, 6, 9, 12, 15 and21 days post-hatch, dph) of Chanos chanos was investigated. The total indispensable amino acids (IAA) contributed to55.62% of the total AA in the egg which reduced to 52.54% on 6 dph. The AA profile of C. chanos was found to be rich invaline (7.99%), leucine (7.51%) and lysine (6.98%) and poor in histidine (2.36%) and methionine (2.47%), indicating a highvaline, leucine and lysine requirement. The docosahexaenoic acid (DHA) content recorded for egg, newly hatched larvae(NHL) and 21 dph larvae were 2.77, 1.36 and 1.94 mg g-1, respectively. The reduction of fatty acids (FAs) was found to bevery high in newly hatched larvae (NHL), especially that of DHA (51%), ARA (26%) and EPA (24%), which indicates thesignificance of these FAs during the embryogenesis of milkfish egg. The trend observed during different stages of AAs andFAs content indicates their requirement during the larval period and those values are to be considered while formulatingfeeds for larval stages of milkfish. Keywords: Embryogenesis, Larval feed, Milkfish larvae, Nutrient requirement

QNZ exposure induces development toxicity and mechanisms of hatching inhibition in large-scale loach (Paramisgurnus dabryanus) embryos

QNZ is a quinazoline-type NF-κB inhibitor and is one of the hot anti-inflammatory drug candidates in recent years. With its development and application, QNZ will inevitably enter the aquatic environment posing a threat to aquatic organisms. To investigate the potential toxicity of QNZ in the early life stages of the organism, this study exposed embryos of large-scale loach (Paramisgurnus dabryanus) to 0, 20, 40, 60, and 80 nM of QNZ. The hatching of embryos was significantly inhibited and hatching time was delayed. We explored the mechanism of hatching delay and failure. The results suggested that QNZ exposure reduced the number of hatching gland cells (HGCs) and hatching enzyme activity. Also, the frequency of spontaneous movements was inhibited by interfering with the expression of genes related to the cholinergic system and skeletal muscle development. Further, QNZ exposure induces a series of morphological changes (spine deformation, pericardial edema, tail deformation, and yolk sac edema) in embryos and newly-hatched larvae, and finally increased the deformity rate and mortality rate of newly-hatched larvae. The information presented in this study will provide a scientific basis for further studies into the potential toxicity of QNZ on aquatic organisms.

Changes in amino acid and fatty acid composition during early development in cobia (Rachycentron canadum)

An estimation of the utilization of endogenous nutrients from the yolk sac that occurs during embryonic and early larval development can be a valuable approach to studying the nutritional requirements of fish larvae. In this study, fertilized eggs, embryos (before the membrane, 24 hours after fertilization), newly-hatched larvae (0-d-old), and open-mouthed larvae (3-day-old, unfed rotifers) samples of cobia (Rachycentron canadum) were collected to determine the amino acid and fatty acid profiles. Crude protein composition varies significantly for cobia during the different stages of development. The total amino acids, except for lysine(Lys), histidine (His), methionine(Met), serine(Ser), and glycine(Gly), had no significant change in the early development stage (P > 0.05); the content of other six essential amino acids (EAA) and six non-essential amino acids (NEAA) was consistent with the changing trend of total essential amino acid. From hatching newly hatched larvae to open-mouthed larvae, except for Leu, Phe and Ser, decreased significantly (P<0.05). From the utilization rate of FAA, the utilization rate of Lys and Leu was the highest (60.26%) and (52.21%) in the embryonic and endogenous nutritional stages, respectively. The water content of the open-mouthed larvae of cobia was significantly higher than that of the fertilized eggs, embryos, and newly hatched larvae (P < 0.05). Three kinds of saturated fatty acids (SFA), five kinds of monounsaturated fatty acids (MUFA), and eight kinds of polyunsaturated fatty acids (PUFA) were detected in the dry samples of each developmental stage. Based on these results, juvenile cobia can thrive with a wide range of crude protein concentrations. Further refinement of commercial cobia production feeds would have beneficial consequences for economic and environmental concerns due to the positive impacts of optimizing the protein component as well as the ability to maintain the rapid growth rates. The results show that the larval development of cobia needs to consume large amounts of n3PUFA (especially DHA and EPA) to improve the larvae’s survival rate. Research methods will always have limitations when evaluating the relationship between early life nutrition interventions and well-being outcomes later in life. This study provides essential information regarding cobia larvae’s fatty acid requirements.

Ontogenetic variation in digestive enzyme activities within embryos and newly-hatched larvae of the tropical spiny lobster, Panulirus ornatus

While there is considerable interest in aquaculture of spiny lobsters (Palinuridae), limited knowledge of nutritional requirements during early life stages remains a major impediment to successful hatchery culture. To better determine endogenous nutrient utilisation during the early life stages of the tropical spiny lobster, Panulirus ornatus, we examined ontogenetic variation in digestive enzyme activities within developing embryos and newly-hatched phyllosoma in the absence of an exogenous food source. Specifically, α-amylase, non-specific esterase, and trypsin-like protease activities were quantified to indicate the relative importance of macronutrients (i.e., carbohydrate, lipid, and protein) and gauge the digestive potential of newly-hatched phyllosoma during transition from endogenous to exogenous nutrient sources. Ontogenetic variation in digestive enzyme activities indicated that lipid, protein, and carbohydrate were sequentially utilised by embryos. Early increase in non-specific esterase activity suggests that lipid is the most critical macronutrient for early embryonic development, with protein and carbohydrate becoming increasingly utilised shortly before and after hatching. The observed peak in trypsin-like protease activity during the first day post-hatch presumably allows phyllosoma to make best use of dietary items that are high in protein at first-feeding. In the absence of an exogenous food source after hatching, changes in digestive enzyme activities suggest that a metabolic shift from protein to lipid occurred, coinciding with the timing of the ‘point-of-no-return’ for Stage I phyllosoma of P. ornatus. Our results highlight the importance of providing an exogenous protein-rich food source to phyllosoma soon after hatch and provide a foundation for further study into broodstock nutrition and egg quality of this species.

Changes in iodide and thyroid hormone levels of hatchery-reared orange-spotted rabbitfish Siganus guttatus (Bloch 1787) during early larval development

This paper elucidates the developmental profiles of iodide and thyroid hormones, thyroxine (T4) and triiodothyronine (T3) in hatchery-reared rabbitfish (Siganus guttatus) during early larval development. The study evaluated the levels of iodide, T4 and T3 tissue content in rabbitfish larvae at 0, 10, 20, 30, 40 and 50 days after hatching (DAH). Under normal rearing conditions, iodide (11.98 ± 4.3 nmol g−1) and thyroid hormones (T4: 0.09 ± 0.01 nmol g−1; T3: 0.01 ± 8.5E-05 nmol g−1 were already detected from newly-hatched larvae and their presence has been attributed from maternal origin. Iodide level sharply peaked at 10 DAH (1416.43 ± 149.6 nmol g−1) which is significantly higher compared to the iodide levels in the larvae at 20, 30, 40 and 50 DAH. The levels of THs gradually increased as the larvae developed with T4 (0.96 ± 0.05 nmol g−1) and T3 (0.03 ± 0.004 nmol g−1) exhibiting a peak on 20 and 30 DAH, respectively, which coincided with the onset of metamorphosis. Thyroid hormone levels gradually decreased which coincided also with the completion of metamorphosis. The present findings indicated a pattern of the rise and fall in iodide and thyroid hormone levels during larval development and its role in metamorphosis of rabbitfish larvae. The study has reported for the first time, the changes in iodide and thyroid hormone levels during the early developmental stage in hatchery-reared rabbitfish and the results are in agreement with those vital actions of thyroid hormones in other fish species.

Activities of digestive enzymes and non-specific immune indicators in <italic>Diodon holocanthus</italic> during larval and juvenile stages

In order to solve the problem of high mortality rate of longspined porcupinefish <italic>Diodon holocanthus</italic> larvae and juveniles, the changes in digestive enzyme activities and non-specific immune indexes from the newly-hatched larvae to juveniles (0-40 d) were studied. The relationship between total length and daily age of <italic>Diodon holocanthus</italic> larvae and juveniles could be fixed to the exponential functions. The activities of amylase, pepsin, trypsin, and lipase were identified in the newly- hatched larvae. During the whole experiment period, the amylase and trypsin activities showed a trend of increasing initially, followed by a decreasing, but then increased again(with the increased daily age), in which amylase activity reached the maximum at 20 d, trypsin activity reached the peak at 5 d, the overall activity of both increased with the daily age but the trypsin activity increased more obviously. Lipase activity decreased rapidly initially (1-5 d), followed by an significant increase (5-10 d), but then decreased drastically again(15-20 d) and maintained at a low level. The activity of pepsin increased gradually from 1 d to 15 d and reached the maximum at 15 d, after which it slowly reduced to the minimum. The activity of lysozyme (LZM) and immunoglobulin M(IgM) showed a trend of increasing first and then decreasing, in which immunoglobulin M activity reached the maximum at 10 d, while lysozyme reached the maximum at 5 d, and after that both decreased slowly and fluctuated and eventually remained at a low level. The above results indicated that the changes of digestive enzyme activities in the larvae and juveniles of <italic>Diodon holocanthus</italic> were closely related to their developmental stages and food types, and various digestive enzyme activities existed in newly-hatched larvae that had not yet eaten food. The non-specific immune indicators increased significantly during the mixed nutrition period when the larvae and juveniles of <italic>Diodon holocanthus</italic> transitioned from endogenous nutrition to exogenous nutrition, and then decreased slowly to a lower level, indicating that the nutritional transformation process had a greater impact on the immune function of larvae and juveniles, higher non-specific immune indicators increased the disease resistance of larvae and juveniles and enhanced the survival rate of breeding.

Early embryonic development of the vulnerable Shalyni barb,Pethia shalynius(Yazdani &amp; Talukdar, 1975)

The present study provides the first detailed early embryonic development of the Shalyni barb, Pethia shalynius (Yazdani & Talukdar, 1975), a vulnerable cyprinid fish occurring in streams and lentic waters of Meghalaya, northeast India. Induced spawning by synthetic hormone injection in May 2019 was conducted to a pair of mature female and male P. shalynius under controlled conditions in a well-aerated aquarium. Fertilized eggs were spherical, 0.75–0.80 mm (approx.) in diameter, transparent, unpigmented and non-adhesive. A total of 22 developmental stages could be categorized under seven broad periods, viz. the zygote, cleavage, blastula, gastrula, segmentation, pharyngula and hatchling. The first cleavage occurred at 15 min post fertilization (mpf), followed by blastulation at 01:23 hr post-fertilization (hpf), gastrulation at 04:20 hpf, initial somite formation at 07:00 hpf, and pharyngula period at 19:20 hpf, respectively. Embryos hatched between 26–27 hpf and the newly-hatched larvae ranged 2.2–2.5 mm in total length. For naturally-declining populations of this vulnerable fish species, inferences drawn from the present study will help provide a baseline data for its conservation and management, and aid the research fields of developmental biology, biotechnology, molecular biology as well as taxonomy of this species.

Salinity and prey concentration on larviculture of killifish Hypsolebias radiseriatus (Cyprinodontiformes: Rivulidae)

The aim of this study was to investigate the tolerance of Hypsolebias radiseriatus larvae to different salinities, and the effects of different prey concentrations and water salinities on the larviculture of this species. Salinity tolerance was tested by subjecting newly-hatched larvae to 96 hours of osmotic shock testing (experiment I) and gradual acclimatization (experiment II) of the following salinities: freshwater (control), 2, 4, 6 and 8 g of salt L-1. A third experiment (experiment III) evaluated three water salinities (S0 - freshwater, S2 - 2 g of salt L-1 and S4 – 4 g of salt L-1) and three initial daily prey concentrations (100, 300 and 500 artemia nauplii larva-1). In experiments I and II, survival was only influenced by the salinity of 8 g of salt L-1 (p &lt; 0.01). After 35 days, weight was only influenced by prey concentration (p &lt; 0.05), with the highest value being with 500 artemia nauplii larva-1. The lowest survival was for 4 g of salt L-1 and for 100 artemia nauplii larva-1. H. radiseriatus larviculture can be carried out in salinity of up to 2 g of salt L-1 and initial daily prey concentrations with 500 artemia nauplii larva-1.

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.

Teratogenic effects of environmentally relevant concentrations of phenanthrene on the early development of marine medaka (Oryzia melastigma)

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants in marine environments and have arouse great concern since they pose adverse effects to marine ecosystem. To determine the potential impacts of environmentally relevant PAHs on early life stages of marine fish, this study exposed embryos of marine medaka (Oryzias melastigma) to 0, 2, 10, 50, and 250 μg/L of phenanthrene (Phe), one of the most abundant PAHs. The results demonstrated that Phe exposure decreased hatching rates, delayed hatching time of embryos, and increased deformity rate of newly-hatched larvae. Exposure to 10 and 50 μg/L Phe decreased the survival rate of marine medaka larvae at 28 days post-fertilization (dpf), and no embryo successfully hatched in 250 μg/L Phe exposure group. Morphology results showed that 10, 50, and 250 μg/L Phe exposure significantly retarded the development of embryos, and 2, 10, and 50 μg/L caused yolk sac edema and pericardial edema in newly-hatched larvae, indicating that low concentrations of Phe could induce developmental cardiac toxicity. Furthermore, the changes in the expression of heart development-related genes were determined, and the results showed that Phe-induced cardiac malformation might be related with fgf8, bmp4, smyd1, ATPase and gata4 genes. Overall, environmentally relevant PAHs could disrupt heart morphogenesis and hatching process of marine medaka, which might have profound consequences for sustainability of fish population.

Effects of pH on the incubation and early development of fish species with different reproductive strategies

Fish reproduction in natural environments tends to occur in conditions, including extreme pH values, ideal for the survival of offspring. In this context, the purpose of this study was to assess the influence of pH on both survival and early development of two fish species, Astyanax lacustris (short-distance migrating fish) and Piaractus mesopotamicus (long-distance migrating fish), with different reproductive strategies. Our experiments were divided into two tests (incubation and larviculture) at five pH levels. First was incubation through a water recirculation system using 2 L incubators followed by larviculture using a 2.5 L aquarium. pH had no influence on the hatching rate of A. lacustris eggs, but affected the yolk-sac diameter, while the newly-hatched larvae had some skeletal disorders. For P. mesopotamicus, pH influenced the hatching rate and perivitelline space, while the newly-hatched larvae had several skeletal disorders. The larviculture of A. lacustris revealed no effect on the survival rate, but the analyzed morphometric variables indicated significant differences between the treatments. An acidic pH negatively influenced the survival rate of P. mesopotamicus, and all morphometric variables also varied significantly between the treatments. We concluded that both the survival and development of A. lacustris and P. mesopotamicus revealed different responses at pH levels during incubation and larviculture tests.

Mercury and selenium distribution in key tissues and early life stages of Yellow Perch (Perca flavescens)

Whereas early life stages are usually considered as particularly sensitive to both organic and inorganic contaminants, field studies assessing contaminant bioaccumulation in these stages are scarce. Selenium (Se) is thought to counteract Hg toxic effects when it is found at Se:Hg molar ratios above 1. However, the variation of this ratio in key fish tissues of different early life stages is mostly unknown. The present study therefore aimed to assess Hg and Se content in gravid female tissues (gonads, muscle, liver, gut, and brain) and different life stages (egg masses, newly hatched larvae (NHL), larvae and juvenile) of Yellow Perch (YP) in a large fluvial lake (Lake Saint-Pierre, Québec, Canada). Se:Hg molar ratios were measured for each compartment in order to fill associated knowledge gaps. Total Hg (THg) and methylmercury (MeHg) concentration varied between tissue according to the following trend: Muscle > Liver > Gut > Brain > Gonads. During YP early life stages, MeHg values increased according to an ontogenetic pattern (mg/kg dw) (mean ± SEM): Egg masses (0.01 ± 0.002) < NHL (0.015 ± 0.001) < Larvae (0.14 ± 0.01) < Juveniles (0.18 ± 0.01). Se concentrations in different YP tissues showed the following trend (mg/kg dw) (mean ± SEM): Gut (3.6 ± 0.1) > Liver (2.5 ± 0.1) > Gonads (1.92 ± 0.06) > Brain (1.26 ± 0.03) > Muscle (1.23 ± 0.06). In YP early life stages, Se concentrations were highest in NHL (3.0 ± 0.2), and then decreased as follows: Egg masses (2.8 ± 0.1) > Larvae (1.37 ± 0.04) > Juveniles (0.93 ± 0.05). Se:Hg molar ratios varied considerably and were systematically above 1. This is the first study to simultaneously report Hg and Se bioaccumulation through fish life cycle.

Effect of dietary taurine in the performance of broodstock and larvae of California yellowtail Seriola dorsalis

The roles of dietary taurine on fish reproductive output and larval development remain poorly understood. A 2-year experiment was conducted where broodstock where fed a taurine-supplemented (2.67% dry diet) or non-supplemented (0.28% dry diet, control) diet, and larvae were fed taurine-enriched or standard-enriched prey, resulting in a 2 × 2 factorial design. Buoyancy, fertilization rate, and fecundity were the main drivers in characterizing eggs from each broodstock group. All these metrics were improved in the taurine-supplemented treatment. Newly-hatched larvae from the taurine-supplemented broodstock had significantly larger yolk-sac volume and 53% more likely to survive to 1st-feeding than those from the control broodstock. All larvae from the control broodstock and fed the control larval diet died by 15 dph, highlighting the essentiality of taurine in this species. However, 30 dph larvae from the treatment where both broodstock and larvae received supplemental taurine were significantly shorter and lighter than those from the other treatments. In conclusion, these results support the importance of dietary taurine in reproductive performance in yellowtail broodstock. Further research is necessary to better understand the interaction between supplementation in broodstock and larval diets.

Delayed timing of successful spawning of an estuarine dependent fish, black bream Acanthopagrus butcheri.

In this paper, we investigate the period of successful spawning for black bream Acanthopagrus butcheri, an obligate estuarine species in southern Australia that typically spawn in spring and early summer. However, back-calculated spawning dates of juveniles sampled in Gippsland Lakes, Victoria from February to May 2016 indicated that spawning was concentrated over a short period in the Austral mid-summer (January), with a second spawning in late summer and early autumn (late February-early March). Ichthyoplankton sampling in the tributary estuaries from October to early December collected substantial numbers of fish larvae, dominated by gobiids, eleotrids and retropinnids of freshwater origin, but no A. butcheri. The lack of A. butcheri larvae was consistent with the delayed successful spawning indicated by juvenile otolith data. Freshwater flows declined from late winter to summer, with consistent salinity stratification of the water column. Dissolved oxygen (DO) concentrations were generally very low below the halocline. These conditions may have delayed the upstream spawning migration of adults or may have been unsuitable for survival of eggs and newly-hatched larvae. Longer-term predictions for climate change in southern Victoria, including the Gippsland Lakes region, are for lower winter-spring freshwater flows, potentially benefiting the reproductive success of A. butcheri through high water-column stratification, but only if DO concentrations are not compromised by a lack of high winter flows needed to flush low DO water from the system.

A lipidomic perspective on the embryogenesis of two commercially important crabs, Carcinus maenas and Necora puber

Lipids play a central role in the metabolism of most organisms. These molecules are paramount during reproduction, when females transfer their internal lipid reserves to build-up oocytes' yolk. The aim of the present study was to understand neutral lipid (NL) dynamics during the embryogenesis of two commercially important crabs, Carcinus maenas (Linnaeus, 1758) and Necora puber (Linnaeus, 1767), using electrospray ionization mass spectrometry (ESI–MS) and tandem MS (ESI–MS/MS). Total lipid extracts were fractionated into NLs and polar lipids (PLs). Triacylglycerol (TAG) profile of NL and fatty acid (FA) profiles of both NLs and PLs were determined in two different embryonic stages: newly-extruded embryos (stage 1, a proxy of maternal investment) and ready-to-hatch embryos (stage 3, a proxy of newly-hatched larvae). In total, 16 molecular species of TAGs and their fatty acyl composition were identified, for the first time in marine invertebrate embryos. During embryogenesis, TAGs bearing C14 to C18 saturated and monounsaturated FAs were preferentially consumed, while TAGs with longer carbon chains and polyunsaturated FAs were selectively retained in the late embryonic stage of both crab species. The analysis of FA profiles revealed that energetic FAs were associated with NLs, while essential FAs were more abundant in PLs. These results evidence the different functions of NLs and PLs as energetic and structural lipids, respectively. The novel approach used in our study provides an unprecedented level of information of lipid dynamics at the molecular level, opening new perspectives in the study of maternal investment and embryogenesis in marine invertabrates.

Biophysical Simulations Support Schooling Behavior of Fish Larvae Throughout Ontogeny

Schooling is very common in adult and juvenile fish, but has been rarely studied during the larval stage. Recent otolith micro-chemistry studies of coral reef fish have demonstrated that cohorts of larvae can move through similar paths and settle within a few meters one from another. However, little is known about the processes involved in the formation and maintenance of these cohorts. Here we use a biophysical modeling approach to examine whether local hydrodynamics, various individual behaviors, or larval schooling can explain cohesive patterns observed for Neopomacentrus miryae in the Gulf of Aqaba/Eilat (Red Sea), and whether schooling is feasible in terms of initial encounter probability and cohesiveness maintenance. We then examine the consequences of schooling behavior on larval settlement success and connectivity. Our results indicate that: (1) Schooling behavior is necessary for generating cohesive dispersal patterns, (2) Initial larval encounter of newly-hatched larvae is plausible, depending mainly on initial larval densities, and patchiness, And (3) schooling behavior increases the rate of larval settlement while decreasing the percentage of realized connections. Together with mounting evidence of cohesive dispersal, this numerical study demonstrates that larval schooling throughout the pelagic phase is realistic, and has a significant effect on settlement success and connectivity patterns. Future research is needed to understand the mechanisms of fission-fusion dynamics of larval cohorts and their effect on dispersal. Our findings should be considered in future efforts of larval dispersal models, specifically in the context of marine connectivity and the planning of marine protected area networks.