Early Juveniles Research Articles

Temporal variations of fish assemblage in the surf zone of the Nakdong River Estuary, southeastern Korea

To assess temporal variations in fish assemblages, fish samples were collected on a monthly basis in the surf zone of the Nakdong River Estuary in 2004. Surveys were conducted at two sites during day and night neap tides using a 10-m beach seine. In total, 2397 specimens (8146.0 g) comprising 27 species and 16 families were collected during the study period. The dominant fish species were Mugil cephalus, Plecoglossus altivelis, Favonigobius gymnauchen, Opsariichthys uncirostris amurensis, and Hyporhamphus sajori, which accounted for 84.6% of the total number of individuals. The fish sampled were primarily small species or the early juveniles of larger species. The species composition and abundance varied greatly, with a peak in the number of individuals in July (summer) and January (winter), and the peak in biomass during July (summer). The catch rate was low in the spring and autumn months due to the low abundance of the dominant species recorded. A cluster analysis revealed that the fish assemblages were characterized by distinct seasonal groups reflecting the reproductive habits of adult fishes. Fish abundance did not significantly differ between the two sites, although a significant difference in their abundance was detected between day and night, with more fish specimens collected at night than during the day at both sites. The Nakdong River Estuary is an important ecosystem for small and/or juvenile fishes, providing a habitat within the estuary suitable for their development and migration.

Effects of Dietary Fish Oil to Soybean Oil Ratio on Survival, Development, and Growth of Early Juveniles of the Blue Swimmer CrabPortunus pelagicus

Identifying suitable alternatives to fish oil for inclusion in formulated diets for aquaculture species is becoming increasingly important; however, relatively few studies have assessed the potential of terrestrial oils as possible replacements for fish oil in diets for marine crustaceans. This study examined the potential of soybean oil as a partial or complete replacement for fish oil in diets for blue swimmer crab Portunus pelagicus juveniles. Seven iso-nitrogenous and iso-lipidic diets were formulated to contain soybean oil to fish oil ratios of 1:0. 3:1. 2:1. 1:1. 1:2. 1:3. and 0:1. They were fed to first-stage crabs over four molts and survival, development, and growth of the crabs were measured. Crabs fed the diet containing soybean oil as the sole lipid source (i.e., soybean oil:fish oil ratio 1:0 treatment) recorded the lowest survival among treatments, significantly longer intermolt duration, and significantly lower specific growth rates compared with other treatments. Improved performance was shown by crabs fed diets containing fish oil at the same, or higher, dietary level than soybean oil but the best survival, shortest intermolt duration, and fastest growth rates were recorded for crabs fed the diet containing the soybean oil:fish oil ratio of 1:1. The results indicated that P. pelagicus juveniles require a balance of dietary n-3 and n-6 fatty acids and thus dietary lipid requirements can be met partially by soybean oil. Diets containing soybean oil are cheaper to produce than traditional fish oil—based diets and soybean oil is a more sustainably sourced ingredient than fish oil. Our results should support further development of the P. pelagicus aquaculture industry.

Vitamin A supplementation enhances Senegalese sole (Solea senegalensis) early juvenile's immunocompetence: New insights on potential underlying pathways.

Senegalese sole (Solea senegalensis) has been considered since the 1990's to be a promising flatfish species for diversifying European marine aquaculture. However, pathogen outbreaks leading to high mortality rates can impair Senegalese sole commercial production at the weaning phase. Different approaches have been shown to improve fish immunocompetence; with this in mind the objective of the work described herein was to determine whether increased levels of dietary vitamin A (VA) improve the immune response in early juveniles of Senegalese sole. For this purpose, Senegalese sole were reared and fed with Artemia metanauplii containing increased levels of VA (37,000; 44,666; 82,666 and 203,000 total VA IU Kg(-1)) from 6 to 60 days post-hatch (early juvenile stage). After an induced bacterial infection with a 50% lethal dose of Photobacterium damselae subsp. damselae, survival rate, as well as underlying gene expression of specific immune markers (C1inh, C3, C9, Lgals1, Hamp, LysC, Prdx1, Steap4 and Transf) were evaluated. Results showed that fish fed higher doses of dietary VA were more resistant to the bacterial challenge. The lower mortality was found to be related with differential expression of genes involved in the complement system and iron availability. We suggest that feeding metamorphosed Senegalese sole with 203,000 total VA IU Kg(-1) might be an effective, inexpensive and environmentally friendly method to improve Senegalese sole immunocompetence, thereby improving survival of juveniles and reducing economic losses.

On the mechanism of orientation and navigation of sockeye salmon underyearlings (Oncorhynchus nerka Walb.) during feeding migration in the inlet–lake–outlet system

Mechanisms that define the choice of migration direction of sockeye underyearlings in the water system of Lake Kurilskoe have been experimentally explored. The choice of direction of feeding migration and maintenance of lake habitats by sockeye are determined by the combination of two factors: water current and lake odor. In the presence of lake odor, early juveniles select migration against the water current; without lake odor they select downstream migration. Such a combination of factors is universal for the orientation of the early juveniles of sockeye that have emerged in the outlet, inlets, and right in the lake.

Early life history traits ofTrematomus scottiin the Bransfield Strait

AbstractEarly life history traits of the blackfin notothen,Trematomus scotti, were investigated through otolith microincrement pattern and stomach content analyses. Post-larval specimens of 12–20 mm standard length (SL) were collected in the Bransfield Strait and adjacent waters during the 2010–11 summer. Catches were unevenly distributed across the surveyed area, yielding a relative abundance of 0.3–3.6 specimens per 1000 m3of filtered sea water. Age estimates ranged from 34 to 67 days, with good consistency and no apparent bias between readings. Based on an exponential model fitted to the age-length dataset, the growth rate was 0.17 mm day-1, corresponding to a daily percentage increment in size of 1.07% SL. In agreement with previous studies, larval hatching occurred at a mean size of 9.0 mm and was spread over a relatively short period, lasting from late December to late January. Prey composition consisted exclusively of copepods, mainly larval stages of copepodites. Feeding intensity ranged from 1–14 prey items per stomach, being positively correlated with larval fish size. In summary,T. scottishares a common early life history strategy with several other notothenioids, consisting of small larvae hatching in summer and overwintering as pelagic early juveniles until the following summer season.

The complex early life history of a marine estuarine-opportunist fish species, <em>Solea turbynei</em> (Soleidae) from temperate South Africa

The early life history stages and ecology of Solea turbynei , a marine estuarine-opportunist species, is described from nursery areas in Algoa Bay, South Africa. Early life history stages were collected over multiple years from known nursery habitats using plankton, fyke and larval seine nets. The larvae are described using morphometric measurements, meristic counts and pigmentation based on 29 individuals. Solea turbynei is differentiated from other Soleidae by the small size at flexion (3-4 mm), low myomere count and presence of two characteristic blotches of pigment on the dorsal fin. This species has a unique early life history strategy in that the larvae progressively span nearshore, surf zone and estuarine habitats with ontogeny. Abundance of preflexion stages peaks in summer in nearshore waters, indicative of peak spawning period but preflexion larvae are present throughout the year, indicating protracted spawning by adults. At flexion stage, larvae utilize surf zones where metamorphosis and settlement takes place. Early juveniles migrate into the sandy lower reaches of estuaries, after which fish take up residency to adulthood. Warm water is important for larval growth and survival in the nearshore, while turbidity shows a positive relationship with recruitment into estuarine nurseries.

Low pH affects survival, growth, size distribution, and carapace quality of the postlarvae and early juveniles of the freshwater prawn Macrobrachium rosenbergii de Man

Acidification of rain water caused by air pollutants is now recognized as a serious threat to aquatic ecosystems. We examined the effects of low pH (control pH 7.5, pH 6, pH 5, pH 4) on the survival, growth, and shell quality of Macrobrachium rosenbergii postlarvae and early juveniles in the laboratory. Hatcheryproduced postlarvae (PL 5) were stocked at 250 PL per aquarium, acclimated over 7 d to experimental pH adjusted with hydrochloric acid, and reared for 30 d. Dead specimens were removed and counted twice a day. After 27 d rearing, all specimens were measured for total length and body weight. Carapace quality was assessed by spectrophotometry. Survival of juveniles was highest at pH 6 (binomial 95% confidence interval 79 - 89%) followed by control pH 7.5 (56 - 68%) and pH 5 (50 - 60%) and was lowest for unmetamorphosed postlarvae and juveniles at pH 4 (43 - 49%). The final median total length and body weight of juveniles were similar at control pH 7.5 (18.2 TL, 50.2 mg BW) and pH 6 (17.7 mm TL, 45.0 mg BW) but significantly less at pH 5 (16.7 mm TL, 38.2 mg BW); at pH 4, the postlarvae did not metamorphose and measured only 9.8 mm TL, 29.3 mg BW. Length frequency distribution showed homogeneous growth at pH 6, positive skew at control pH 7.5 and pH 5, and extreme heterogeneity at pH 4. The carapace showed different transmittance spectra and lower total transmittance (i.e. thicker carapace) in juveniles at pH 7.5, pH 6, and pH 5 than in unmetamorphosed postlarvae and juveniles with thinner carapace at pH 4. Thus, survival, growth, size distribution, and carapace quality of M. rosenbergii postlarvae and early juveniles were negatively affected by pH 5 and especially pH 4. The thinner carapace of the survivors at pH 4 was mostly due to their small size and failure to metamorphose. Natural waters affected by acid rain could decimate M. rosenbergii populations in the wild.

Does the presence of microplastics influence the acute toxicity of chromium(VI) to early juveniles of the common goby (Pomatoschistus microps)? A study with juveniles from two wild estuarine populations

Toxicological interactions between microplastics (MP) and other environmental contaminants are of grave concern. Here, the potential influence of MP in the short-term toxicity of chromium to early juveniles of Pomatoschistus microps was investigated. Three null hypotheses were tested: (1) exposure to Cr(VI) concentrations in the low ppm range does not induce toxic effects on juveniles; (2) the presence of microplastics in the water does not influence the acute toxicity of Cr(VI) to juveniles; (3) the environmental conditions of the natural habitat where fish developed do not influence their sensitivity to Cr(VI)-induced acute stress. Fish were collected in the estuaries of Minho (M-est) and Lima (L-est) Rivers (NW Iberian Peninsula) that have several abiotic differences, including in the water and sediment concentrations of various environmental contaminants. After acclimatization to laboratory conditions, two 96h acute bioassays were carried out with juveniles from both estuaries to: (i) investigate the effects of Cr(VI) alone; (ii) investigate the effects of Cr(VI) in the presence of MP (polyethylene spheres 1–5μm ∅). Cr(VI) alone induced mortality (96h-LC50s: 14.4–30.5mg/l) and significantly decreased fish predatory performance (≤74%). Thus, in the range of concentrations tested (5.6–28.4mg/l) Cr(VI) was found to be toxic to P. microps early juveniles, therefore, we rejected hypothesis 1. Under simultaneous exposure to Cr(VI) and MP, a significant decrease of the predatory performance (≤67%) and a significant inhibition of AChE activity (≤31%) were found. AChE inhibition was not observed in the test with Cr(VI) alone and MP alone caused an AChE inhibition ≤21%. Mixture treatments containing Cr(VI) concentration ≥3.9mg/l significantly increased LPO levels in L-est fish, an effect that was not observed under Cr(VI) or MP single exposures. Thus, toxicological interactions between Cr(VI) and MP occurred, therefore, we rejected hypothesis 2. In the presence of MP, the negative effect caused by high concentrations of Cr(VI) on the predatory performance was significantly reduced in L-est fish but not in M-est fish, and Cr(VI) concentrations higher than 3.9mg/l caused oxidative damage in L-est fish but not in M-est fish. The acclimatization and test conditions were similar for fish from the two estuaries and these ecosystems have environmental differences. Thus, long-term exposure to distinct environmental conditions in the natural habitat during previous developmental phases influenced the sensitivity and responses of juveniles to Cr(VI), therefore, we rejected hypothesis 3. Overall, the results of this study indicate toxicological interactions between MP and Cr(VI) highlighting the importance of further investigating the combined effects of MP and other common contaminants.

Understanding recruitment patterns of historically strong juvenile year classes in redfish (Sebastes spp.): the importance of species identity, population structure, and juvenile migration

Genetic analyses were undertaken on archived otoliths from juveniles representing historically strong year classes of northwest Atlantic redfish (Sebastes spp.) and on tissue samples from adults of known species and population of origin. The results indicated that the species composition of a year class is key information for understanding recruitment dynamics, with redfish species having distinct population-associated patterns of spatial dispersion. In the Gulf of St. Lawrence – Laurentian Channel area (GSL–LCH), the last strong year class (which supported the fishery for more than 30 years) belonged to Sebastes mentella and originated from the area. In contrast, four year classes that appeared abundant at young ages in research surveys in GSL–LCH but contributed only marginally to the adult population and the fishery of the region belonged to Sebastes fasciatus and carried the genetic signature of the adult population from the slope of the Newfoundland Grand Banks. Ocean currents and spatiotemporal trends in abundance-at-length suggest that the latter population uses the Gulf of St. Lawrence as a nursery area, with larvae and early juveniles drifting toward the Gulf of St. Lawrence and older juveniles migrating back to the slope of the Grand Banks after about 5–6 years. It is suggested that juvenile migration behaviour is a postsettlement process that plays an important role in redfish recruitment dynamics and carries both demographic and evolutionary implications.

Diet and feeding strategies of mesopelagic fishes in the western Mediterranean

Myctophids, gonostomatids and sternoptychids are the most abundant teleosteans worldwide and constitute an important assemblage of the mesopelagic ecosystem, functioning as vehicles of energy and matter through trophic webs. This study concentrates on the trophic ecology of the most abundant mesopelagic fishes of the western Mediterranean (WM) based on stomach content analysis. The myctophids (in this study: Benthosema glaciale, Ceratoscopelus maderensis, Lobianchia dofleini, Myctophum punctatum, Hygophum benoiti, Hygophum hygomii, Lampanyctus crocodilus, Lampanyctus pusillus and Notoscopelus elongatus) perform extensive diel migrations across the water column, between the surface to as deep as 1000m, interacting with plankton and micronekton at multiple depths, and generally feeding in the epipelagic layers at night. In contrast, the gonostomatids Cyclothone braueri, Cyclothone pygmaea, and the sternoptychid Argyropelecus hemigymnus remain below epipelagic layers, feeding at different times throughout the day and night. The diet composition, trophic niche breadth and prey selectivity of 11 of these fish species were determined for juvenile and adult individuals from two surveys performed in December 2009 and July 2010 in the western Mediterranean Sea. The number of prey items varied among species, e.g. Myctophum punctatum was the species with the highest feeding intensity, reaching ca. 700 prey items in a stomach, whereas the mean number of prey in Cyclothone braueri was low (usually 1 or 2 prey per stomach). A dietary shift towards larger prey was evident from juveniles to the largest and oldest adult individuals, despite trophic niche breadths did not increase with body length for any of these mesopelagic species. The diets of the small gonostomatids, sternoptychid and early juveniles of myctophids were dominated by non-calanoid copepods, ostracods, and other small zooplankton, whereas medium-sized myctophids, e.g. L. dofleini or H. benoiti, preyed mainly on calanoids. The oldest stages of L. crocodilus and N. elongatus fed mostly on macrozooplankton and micronekton. There was high diet overlap among mesopelagic fish species and strong heterogeneity in diet composition at intraspecific level. Nevertheless, some species showed certain degree of segregation of food resources, determined by the developmental stage or spatial distribution, and positive selection towards particular prey items. The Chesson’s electivity index showed that L. dofleini, N. elongatus, L. crocodilus and L. pusillus preyed selectively on euphausiids; B. glaciale was selective on the calanoid genus Pleuromamma, and C. maderensis preferred to feed on larvaceans in autumn. The two congeneric species of Hygophum consumed a high number of food items, but H. hygomii showed positive selection for euphausiids, whilst H. benoiti preferred small corycaeid copepods. Overall, the main trophic difference among mesopelagic fishes in the WM was observed between the small non-migratory species that do not evidence a diel rhythm, feeding during both day- and night-time on small zooplankton, and the largest-sized myctophids, which fed on meso- and macrozooplankton and, more occasionally, on small fishes. Mediterranean midwater fishes can be characterised by the adoption of mixed feeding strategies, with varying degrees of specialisation on different prey types that allow flexibility in a changeable environment.

Ontogenetic dietary and habitat shifts in goliath grouper Epinephelus itajara from French Guiana

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 27:155-168 (2015) - DOI: https://doi.org/10.3354/esr00661 Ontogenetic dietary and habitat shifts in goliath grouper Epinephelus itajara from French Guiana C. Artero1,2,4,*, C. C. Koenig2, P. Richard3, R. Berzins1, G. Guillou3, C. Bouchon4, L. Lampert5 1Office National de la Chasse et de la Faune Sauvage, 44 rue Pasteur, BP 10808, 97338 Cayenne cedex, French Guiana 2Florida State University Coastal and Marine Laboratory, 3618 Coastal Highway 98, St Teresa Beach, FL 32358, USA 3Littoral Environnement et Sociétés, UMR 7266 CNRS-Université de La Rochelle, 2 rue Olympa de Gouges, 17000 La Rochelle, France 4Université des Antilles et de la Guyane, Labex CORAIL, équipe DYNECAR, 97159 Pointe à Pitre, Guadeloupe (French West Indies) 5Institut Français de Recherche pour l’Exploitation de la MER, Dyneco/Pelagos, 29280 Plouzané, France *Corresponding author: celine.artero.merou@gmail.com ABSTRACT: The ecology, particularly the trophic ecology, of the Critically Endangered goliath grouper Epinephelus itajara (Lichtenstein 1822) in French Guiana (France) is relatively unknown. Such information would provide a better understanding of the role that goliath groupers play in the marine ecosystem of French Guiana. This study focused on the feeding ecology of the goliath grouper through stomach-content and stable-isotope analyses of captured specimens. The dietary composition of goliath groupers in French Guiana was similar to that of goliath groupers from other areas of the species’ range. However, in French Guiana, goliath groupers exhibited an ontogenetic shift in diet that has not been demonstrated elsewhere. Crustaceans, primarily crabs, were dominant in the diet of smaller individuals (<120 cm), whereas demersal fishes, particularly catfish (Siluriformes), dominated the diet of larger individuals. Analysis of δ13C and δ15N in muscle samples indicated that: (1) larger fish fed more on higher trophic levels; (2) low seasonal and spatial variation existed in the diet; and (3) an apparent migration of early juveniles occurred from mangrove areas to rocky reefs. In French Guiana, adult and juvenile goliath groupers share marine rocky habitat, and the data suggest they may avoid food competition by a shift in diet with size. KEY WORDS: Epinephelidae · Critically Endangered species · Stomach contents · Carbon and nitrogen stable isotopes · Dietary shift · Migration · Mangroves · Diet Full text in pdf format PreviousNextCite this article as: Artero C, Koenig CC, Richard P, Berzins R, Guillou G, Bouchon C, Lampert L (2015) Ontogenetic dietary and habitat shifts in goliath grouper Epinephelus itajara from French Guiana. Endang Species Res 27:155-168. https://doi.org/10.3354/esr00661 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 27, No. 2. Online publication date: April 15, 2015 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2015 Inter-Research.

Evaluating the effects of temperature, salinity, starvation and autotomy on molting success, molting interval and expression of ecdysone receptor in early juvenile mud crabs, Scylla paramamosain

Newly molted first stage juvenile mud crabs (C1), Scylla paramamosain, were subjected to different temperatures (14, 20, 26, 32 and 39°C), salinity (5, 10, 20, 30 and 40), starvation conditions and autotomy (for the autotomy experiment, the second stage crabs (C2) were used) to assess their effects on molting success, molting interval and corresponding expressions of the crab's ecdysone receptor (EcR). The results showed that at a low temperature of 14°C no molt occurred with a subdued EcR mRNA level detected. In contrast, a higher temperature of 32°C induced a significant increase in the expression of EcR gene and dramatically reduced the C1 molting interval as compared to other treatments. As the temperature further increased to 39°C and after a period of 6 or more hours the expression of EcR gene dropped abruptly and all C1 crabs died without molt. On the other hand, a low salinity of 5 increased EcR mRNA levels at 72h and shortened the molting interval significantly whilst high salinity of 40 resulted in the opposite. No significant difference in percentage molting success was detected among salinity from 10 to 40. When C1 crabs were subjected to starvation for longer than 48h, the expression of EcR was found to be significantly repressed as compared to the feeding control, in which none of the starved crabs successfully molted. Meanwhile, although the molting success of C2 crabs was not significantly affected by autotomy, the molting interval significantly increased from 5.8days for intact crabs to 6.2days for the autotomized crabs. Interestingly, when compared to intact crabs, the expression level of EcR gene in autotomized crabs was at first repressed (i.e. during the first 120h) but increased sharply to a level significantly higher than the control at 134h (i.e. during premolt stage of the autotomized crabs). Our results showed that temperature, salinity, starvation and autotomy all affected molting of early juvenile mud crabs and changes in their EcR mRNA levels appeared to play an important role in regulating the molting process. The current experiment also showed that S. paramamosain early juveniles could withstand a broad range of temperatures and salinity, therefore highlighting their adaptability to the seasonal variation in salinity and temperature of natural habitat.

Daily otolith growth and ontogenetic geochemical signatures of age-0 anchovy (Engraulis encrasicolus) in the Gulf of Cádiz (SW Spain).

The European anchovy fishery in the Gulf of Cádiz (ICES Division IXa South) is largely influenced by age-0 individuals. Knowledge of young of the year growth dynamics is crucial for management, yet data on daily growth are lacking in the area. Linking growth patterns to the environment requires information on habitat occupancy through ontogeny of the fish that reach the fishery, as anchovy use different areas of the Gulf and the Guadalquivir Estuary through development. We describe the growth dynamics of age-0 anchovy through otolith microstructure analysis, and couple these data with data on microchemical signals in the otoliths to shed light into habitat use and growth dynamics in the area. Age-0 anchovy captured in September, 2011 in the Gulf ranged from 3 to 6 months old for similar sizes, with average growth rates varying twofold. Individual non-linear growth curves showed that maximum otolith growth was positively correlated with the date of spawning, which in turn was negatively correlated with the time to reach maximum growth. There was no correlation between growth parameters and body length or condition (Fulton K) at capture. The strontium:calcium (Sr/Ca) and magnesium:calcium (Mg/Ca) ratios were significantly lower at the edge of the otolith (approximately the age of capture) than at ages corresponding to larval and early juveniles (&lt;60 days old), but values fell within typical estuarine-dwelling species. The barium:calcium ratio (Ba/Ca) increased significantly in the edge of the otolith, which possibly resulted from residency in highly productive coastal waters or from ontogenetic effects. The variance in otolith elemental ratios was larger at otolith back-calculated ages around 50 days old, age which coincides with the presumed closer dependence of estuarine waters. Our data are a first step towards understanding the contribution of the estuarine system to the fishery of anchovy in the Gulf. The limitations of the approach and future steps are discussed.

CDNA structure and the effect of fasting on myostatin expression in walking catfish (Clarias macrocephalus, Günther 1864).

We cloned and sequenced the myostatin (MSTN) gene of walking catfish and characterized its expression under different conditions. The full cDNA sequence of MSTN was 1,784 bp, containing an open reading frame of 1,191 bp, which encoded 396 amino acids. The deduced MSTN sequence contained functional sites similar to other members of TGF-β superfamily, including the proteolytic processing site and nine conserved cysteines in the C-terminal. Walking catfish MSTN mRNA was strongly expressed in skeletal muscle and brain tissues, consistent with the expression profiles of MSTN-1 isoform in other teleosts. Temporal expression analysis revealed that the MSTN was expressed at the highest levels in 1-week-old larvae and adults, but was lowest in early juveniles. A fasting-re-feeding experiment was used to evaluate the effects of starvation on growth and MSTN expression in juvenile walking catfish for 28 days. MSTN transcript levels increased significantly (threefold) after 7 days of fasting (P < 0.05) compared with the fed control. Subsequently, MSTN expression levels decreased 1.6-fold when fasting was extended to 14 days. Although re-feeding decreased the MSTN expression relative to the levels of the fed control, the period was not long enough for growth recovery of the juveniles. Our results supported a role of MSTN as a negative regulator of muscle growth and, possibly, a role in energy conservation in fish.

Susceptibility to an inoculum of infectious hypodermal and haematopoietic necrosis virus (IHHNV) in three batches of whiteleg shrimp Litopenaeusvannamei (Boone, 1931).

The present study evaluated the susceptibility of three different batches of whiteleg shrimp Litopenaeus vannamei from Mexico to an inoculum of infectious hypodermal and haematopoietic necrosis virus (IHHNV). Each of the three shrimp batches came from a different hatchery. Because of their origin, it was possible that the genetic makeup of these batches was different among each other. The three batches tested showed differences in IHHNV susceptibility. Here, susceptibility is defined as the capacity of the host to become infected, and it can be measured by the infectivity titer. Susceptibility to IHHNV was observed in decreasing order in shrimp from batch 1 (hatchery from El Rosario, Sinaloa), batch 3 (hatchery from Nayarit) and batch 2 (hatchery from El Walamo, Sinaloa), respectively. The largest susceptibility difference between batches was 5012 times, and that between early and late juveniles from the same batch was 25 times. These results indicate that within a species, susceptibility to a pathogen such as IHHNV can have large differences. Susceptibility to pathogens is an important trait to consider before performing studies on pathogenesis. It may influence virological parameters such as speed of replication, pathogenicity and virus titer. In order to evaluate the potential use of IHHNV as a natural control agent against white spot syndrome virus (WSSV), it is necessary to know host susceptibility and the kinetics of IHHNV infection. These features can help to determine the conditions in which IHHNV could be used as antagonist in a WSSV infection.

Effects of microplastics on juveniles of the common goby (Pomatoschistus microps): Confusion with prey, reduction of the predatory performance and efficiency, and possible influence of developmental conditions

Microplastics (MP) are ubiquitous contaminants able to cause adverse effects on organisms. Three hypotheses were tested here: early Pomatoschistus microps juveniles can ingest MP; the presence of MP may reduce fish predatory performance and efficiency; developmental conditions may influence the prey selection capability of fish. Predatory bioassays were carried out with juveniles from two estuaries with differences in environmental conditions: Minho (M-est) and Lima (L-est) Rivers (NW Iberian coast). Polyethylene MP spheres (3 types) alone and in combination with Artemia nauplii were offered as prey. All the MP types were ingested, suggesting confusion with food. Under simultaneous exposure to MP and Artemia, L-est fish showed a significant reduction of the predatory performance (65%) and efficiency (up to 50%), while M-est fish did not, suggesting that developmental conditions may influence the prey selection capability of fish. The MP-induced reduction of food intake may decrease individual and population fitness.

Effects of food type and feeding frequency on the performance of early juveniles of the sea urchin Loxechinus albus (Echinodermata: Echinoidea): Implications for aquaculture and restocking

Abstract Sustainable aquaculture and restocking of the sea urchin Loxechinus albus will demand a reliable source of high-quality juveniles. Culture techniques for L. albus must be refined on several levels to scale up to commercial production. In this study, the effects of different natural foods (six algal foods and one animal food) and the feeding frequency (three regimes: one continuous and two intermittent) on the growth and feeding of L. albus juveniles with a test diameter of ca. 5 mm belonging to a single 5-month-old cohort were investigated. Juveniles fed with Rhodophyta: Porphyra sp. and Gracilaria chilensis grew significantly faster (wet body weight and test diameter) than those fed other foods, although these food items are not frequently observed in the gut contents of wild populations. Juveniles fed with Macrocystis pyrifera showed the lowest growth rates. Differences in ingestion rates and the food conversion ratio (FCR) were principally associated with organic matter and protein content in foods. Although L. albus have been described as generalist herbivores, in this study, they ingested an animal food (marine sponge) and were able to grow significantly better than juveniles fed with M. pyrifera . Juveniles did not show evidence of a compensatory mechanism with a decrease in the frequency of food availability. The growth, ingestion rates and FCR in early juveniles were positively related with feeding frequency, suggesting that continuous feeding is the best and most efficient dietary treatment in terms of growth. Porphyra sp. and G. chilensis , as single species diets, are promising alternatives for the development of cultures of L. albus juveniles; however, further studies are required to compare the efficient use of algae as food (e.g., versus artificial feeds).

Early development and allometric growth patterns of beluga Huso huso (Linnaeus, 1758)

Summary Hatchery reared beluga (Huso huso) were observed from hatching until the juvenile stage in order to analyse their early development and allometric growth patterns using bivariate and multivariate allometric analyses for different body regions (e.g. head, trunk, tail) and test whether there existed similarities in the growth patterns of beluga compared to other fish species, especially other sturgeon species belonging to the genus Acipenser. Results from Principle Component Analysis on morphometric characters (total length, head length, head height, trunk length, rostrum length and eye diameter) in specimens showed that there were shifts in the relative growth of these characters in early development (length at metamorphosis, Lm). A first stage comprised of hatching to 17.03 ± 0.14 mm in total length (Lm1), a second stage was between 17.03 and 25.41 ± 0.21 mm (Lm2), and a third developmental stage at larger sizes (larvae larger than Lm2). Most morphological (feeding, swimming, sensorial and respiratory systems) and morphometric changes in beluga development took place during the second growth stanza, which may be considered as a transitional period from the larval to the juvenile stage, whereas at larger sized fish may be considered as early juveniles. The allometric growth of beluga matched developmental and behavioral events (e.g. swimming-up, schooling and free benthic swimming) observed in the early ontogeny of this species, and showed the priority of growth of the cephalic and tail regions in beluga pre-larvae for feeding and respiratory functions, and the tail for cruising and escape reactions prior to the full development of the digestive system. This study provides information on the ontogeny of the species, establishing a reference for its normal development that might be useful for evaluating the suitability and quality of fish produced for restocking purposes and improving the current beluga management plans.

The Absence of Gumfoot Threads in Webs of Early Juveniles and Adult Males ofPhysocyclus globosus(Pholcidae) is not Associated with Spigot Morphology

Summary Gumfoot threads attached to the substrate may allow spiders to retain prey. These threads were recently discovered in adult females of Pholcidae spiders, and are similar to those in Theridiidae. We report for the first time the presence of gumfoot threads in the webs of immature spiders (fifth instar juveniles) of the pholcid Physocyclus globosus Taczanowski, 1874, and their absence in the webs of first and second instar juveniles and adult males. The bands of adhesive silk were shorter in fifth instar nymphs than in adult females, and had continuous rather than discrete adhesive droplets like the webs of two other adult female pholcid spiders. In Pholcidae, the large spigot on the anterior lateral spinnerets, which presumably produces glue, was relatively thicker in adult females and first instar juveniles than in adult males, which do not produce gumfoot threads. Therefore, we suggest that the ontogenetic origin of gumfoot threads may not be associated with changes in spigot morphology. In addit...

Age and growth of Benthosema pterotum (Alcock, 1890) (Myctophidae) in the Oman Sea

Summary Juvenile and adult specimens of Benthosema pterotum (skinnycheek lanternfish) were collected during several surveys conducted on the Iranian continental shelf of the Oman Sea. Age was estimated by enumeration of growth increments in sagittae otolith sections on the assumption of their daily deposition. Three distinct growth zones in otolith microstructure (central, middle, and external) were defined. These three zones presumably represent increments deposited during successive life history stages, characterized by a different migratory behavior and depth occurrence. The number of increments in the central zone of the B. pterotum otolith (26.8 on average) was thus far one of the lowest in myctophid species studied. A negative correlation between the number of increments in the central and middle zones was observed. This might suggest a functional relation between these two periods of early life history, when fewer larvae in the epipelagic layers may be compensated by a longer non-migratory behavior of metamorphosis larvae and early juveniles. The maximum number of growth increments in B. pterotum otoliths, i.e. 315, indicated a short lifespan of probably <1 year. The relationship between otolith length and standard length was described by linear regression model (r2 = 0.902), and between the body length and weight as an isometric growth in 274 juvenile and adult specimens (r2 = 0.922). The growth model estimated only for juveniles and adults was curvilinear (SL = 1.150 × Age0.616; r² = 0.868). Back-calculated hatch dates might suggest a spawning season of B. pterotum from May to September, but due to the limited number of investigated specimens a prolonged spawning cannot be excluded. Further trials are needed to measure the population parameter dynamics.