Characterization of the pelagic ecosystem in surface waters of the northern Gulf of St, Lawrence in early summer: the larval redfish-Calanus-microplankton interaction

In June 1989, the water column along a transect in the north-central Gulf of St Lawrence was thermally stratified (10–14^oC at the surface; 0-l^oC at 30 m). In the surface layer, nitrate and chlorophyll concentrations were very low; the mean concentration of chlorophyll a > 5 μm in the subsurface maximum was 0.26 μg1^-1. Autotrophic and (presumably) heterotrophic flagellates and dinoflagellates were the most abundant micro-plankton. In this system, redfish (Sebastes spp.) larvae and the planktonic copepod Calanus finmarchicus overwhelmingly dominated the ichthyoplankton and zoo-plankton, respectively. Redfish larvae, Calanus females and Calanus eggs were most abundant in the surface layer (0–25 m) day and night. Daily specific egg production rates of Calanus, calculated from shipboard incubations of females, approached the predicted maximal level for this species at the ambient temperature of the surface layer, indicating no or little food limitation. The redfish larvae were feeding almost exclusively on the Calanus eggs and were found in greatest abundance along the transect where Calanus egg production rates (eggs m^-2 day^-1), calculated from the product of the specific egg production rate and female concentration, were highest. The mono-specificity of the larval redfish diet and the codom-     

Time of first feeding of Atlantic halibut, Hippoglossus hippoglossus L., larvae

Atlantic halibut, Hippoglossus hippoglossus (L.), eggs originating from one female were evenly distributed between four silos (4.8 m³) shortly prior to hatching. At days 30, 35, 40 and 44 after hatching [i.e. 200, 230, 260 and 290 day-degrees (days^o)], the larvae were successively collected and transferred to indoor start feeding tanks, and larvae were offered a diet of instar II Artemia nauplii which had been enriched short time (24 h). A significant correlation was found between the age of the larvae and onset of first feeding. The larvae transferred to start-feeding incubators at 290 days^o were able to capture Artemia only a few hours after transfer, whereas it took 6 days for the larvae transferred at 200 days^o to reach a corresponding ingestion level. Larval growth was also positively correlated to both larval age and prey consumption. However, there were no differences in survival between the larval groups.     

Contributions to the larval biology of the red-lipped conch, Strombus luhuanus L. 1758, with respect to seed production for mariculture

Spawning behaviour and embryology of the red-lipped conch, Strombus luhuanus L. 1758 (Strombidae, Gastropoda), was investigated from 4 April to 19 May 1991, at Okinawa, southern Japan. At the laboratory and at a water temperature of 22.5-23.5^oC, veliger larvae developed 92 h after spawning. In all, 2140 larvae were examined for morphometric data. Growth and development was monitored at different water temperatures (23, 28 and 33^oC), in natural sea water filtered through 150-μm, 60-μm and 1-μm screens and when fed various combinations of food organisms, namely Chaetoceros sp., Dunaliella sp. and Pavlova sp. The minimum duration of the pelagic period of the larvae was 14.5 days. Infestation by parasites was the main cause of high larval mortality before the age of 10-12 days if the water was not filtered at a minimum of 60 μm. Inappropriate food diversity was the most significant source of mortality beyond this age. The maximum age reached during all rearing experiments was 16 days. Under optimized feeding conditions and in natural sea water filtered at 1-60 μm, the pelagic period of S. luhuanus larvae lasted 16.5 to 17.4 days (95% confidence limits). Optimum water temperature was 23-28^oC. A stepwise increment of filter sizes and a contemporary provision of a combination of specific supplementary food organisms is advised through grow-out of the larvae.     

Growth and mortality of larval anchoveta Engraulis ringens,in northern Chile during winter and their relationship with coastal hydrographic conditions

Larval growth, age, growth effect and instantaneous mortality were estimated in anchoveta, Engraulis ringens, collected biweekly during the austral winter of 2014 in nearshore waters off Bay of Antofagasta (23°41′W–70°30′S), northern Chile. Through measuring standard length (SL) and sagitta microstructure analysis, it was estimated that the growth rate of E. ringens larvae decreased from June (0.85 mm day^?1) to August (0.50 mm day^?1). However, the water temperature was homogeneous during the sampling dates (14.6, 15.2, 14.4, and 14.6°C), suggesting that the decelerating larval growth was not linked to changes in sea temperature. Additionally, larvae with slow growth have larger otoliths compared with conspecifics with fast growth (growth effect). Larval mortality rates tended to decrease until the middle of July (0.18 per day) but increased to 0.25 per day in early August, which coincided with lower food availability (i.e., chlorophyll‐a, 2.7–5.6 mg m^?3) and a high occurrence of smaller larvae (1.58–11.5 mm). Partial least squares analysis indicates low covariance between the biological and oceanographic variables (PLS: 11.71%), suggesting that other factors, such as parental effects, may explain the abrupt decrease in the larval growth rates.     

Habitat associations of dolphinfish larvae in the Gulf of Mexico

The aim of this study was to investigate the role of the northern Gulf of Mexico (Gulf) as essential habitat of common dolphinfish (Coryphaena hippurus) and pompano dolphinfish (C. equiselis) during early life and to characterize conditions in which they were found. Eight ichthyoplankton surveys were conducted during the summer months from 2007 to 2010 in northern Gulf waters off Texas and Louisiana (26–28°N, 87–93°W), during which 1145 dolphinfish larvae were collected. C. hippurus, the dominant dolphinfish species, were collected in 57% of sampling sites with an overall mean density of 0.73 larvae 1000 m^?3, whereas C. equiselis were only collected at 18% of sites with a mean density of 0.12 larvae 1000 m^?3. Generalized additive models (GAMs) were used to examine the relationship between several environmental parameters and C. hippurus presence/absence and density. Both presence/absence and density GAMs indicated that catches of C. hippurus larvae increased near fronts and eddies and that increased abundances were most strongly associated with higher salinities and cooler temperatures. In addition, our models showed that C. hippurus larvae were positively associated with C. equiselis larvae, suggesting that C. hippurus and C. equiselis use similar habitats. Results of this study indicate that the Gulf may represent important spawning and/or nursery habitat of dolphinfishes and that mesoscale features and physicochemical conditions influence the distribution and abundance of C. hippurus larvae in this region.     

Influences of El Niño on assemblages of mesopelagic fish larvae along the Pacific coast of Baja California Sur

Seasonal assemblages of mesopelagic fish larvae and changes related with environmental factors (plankton biomass, sea surface temperature anomaly, upwelling, and the multivariate El Niño index) were investigated. From 1982 to 1987, 16 oceanographic cruises were carried out along the Pacific coast of Baja California Sur, Mexico. Larvae of 42 mesopelagic fish taxa were collected. Larval abundance was highly variable during the studied period, but summer months coincided with higher abundance (>200 larvae under 10 m²). Larval assemblages were dominated by three of the most common species of tropical (Vinciguerria lucetia, Diogenichthys laternatus) and subtropical affinity (Triphoturus mexicanus). A group of species of tropical affinity (Diplophos proximus, Diaphus pacificus, Benthosema panamense) was useful for distinguishing the 1982–84 El Niño event, and an assemblage of larvae of temperate affinity (Symbolophorus californiensis, Melamphaes lugubris, Bathylagus ochotensis, Leuroglossus stilbius, Protomyctophum crockeri) characterized ‘normal’ years (mid‐1984 to mid‐1987).     

Ocean distribution and habitat associations of yearling coho (Oncorhynchus kisutch) and Chinook (O. tshawytscha) salmon in the northern California Current

Yearling juvenile coho and Chinook salmon were sampled on 28 cruises in June and September 1981–85 and 1998–07 in continental shelf and oceanic waters off the Pacific Northwest. Oceanographic variables measured included temperature, salinity, water depth, and chlorophyll concentration (all cruises) and copepod biomass during the cruises from 1998–07. Juvenile salmonids were found almost exclusively in continental shelf waters, and showed a patchy distribution: half were collected in ～5% of the collections and none were collected in ～40% of the collections. Variance‐to‐mean ratios of the catches were high, also indicating patchy spatial distributions for both species. The salmon were most abundant in the vicinity of the Columbia River and the Washington coast in June; by September, both were less abundant, although still found mainly off Washington. In June, the geographic center‐of‐mass of the distribution for each species was located off Grays Harbor, WA, near the northern end of our sampling grid, but in September, it shifted southward and inshore. Coho salmon ranged further offshore than Chinook salmon: in June, the average median depth where they were caught was 85.6 and 55.0 m, respectively, and in September it was 65.5 and 43.7 m, respectively. Abundances of both species were significantly correlated with water depth (negatively), chlorophyll (positively) and copepod biomass (positively). Abundances of yearling Chinook salmon, but not of yearling coho salmon, were correlated with temperature (negatively). We discuss the potential role of coastal upwelling, submarine canyons and krill in determining the spatial distributions of the salmon.     

Feeding and digestion in the caridean shrimp larva of Palaemon elegans Rathke and Macrobrachium rosenbergii (De Man) (Crustacea: Palaemonidae) on live and artificial diets

Larvae of two caridean shrimp species, Macrobrachium rosenbergii (De Man) and Palaemon elegans Rathke, were fed live and artificial diets. P. elegans larvae fed exclusively live Artemia salina (15 nauplii mL^?1) developed into first postlarval stage (PL1) within 12 days at a temperature of 25°C and salinity 32.5 g L^?1. Their survival and mean total length at this stage were 88.5% and 6.7 mm respectively. M. rosenbergii larvae fed on 15 Artemia mL^?1 started to metamorphose into PLl within 24 days at 29–30°C and 12 g L^?1. Attempts to completely replace live Artemia for rearing P. elegans during early stages failed, and only a partial replacement was achieved for the larvae of both species. P. elegans larvae survived (49%) solely on a microgranulated diet (Frippak PL diet) from stage zoea (Z) 4–5 to PL1. Similarly, a microencapsulated diet (Frippak CD3) also sustained M. rosenbergii larvae from Z5–6 to PL1 with a 28% survival. Development of the larvae of both species was retarded by 2–3 days and their survivals were lower than those fed on the live diet. The inability of the early larvae of these caridean species to survive on artificial diets is attributed to their undeveloped guts and limited enzymatic capabilities. Trypsin activity in the larvae was determined for all larval stages. It was found that the highest trypsin activity, at stage Z4–5 in P. elegans and at stage Z5–6 in M. rosenbergii, coincides with a rapid increase in the volume of the hepatopancreas and the formation of the filter apparatus. These morphological changes in the gut structure appear to enable the larvae to utilize artificial diets after stage Z5–6. Low larval trypsin activities may be compensated by the easily digestible content of their live prey during early larval stages (Z1–Z4/5) and by longer gastroevacuation time (GET) and almost fully developed guts during later stages.     

Optimizing stocking density and microalgae ration improves the growth potential of tropical black‐lip oyster,Saccostrea echinata,larvae

The combined effects of stocking density and microalgae ration on survival and size of Saccostrea echinata larvae were studied in two‐factor experiments for the major developmental stages: D‐veliger (1‐day posthatch [dph], Experiment 1), umbonate (12 dph, Experiment 2), and eyed (19 dph, Experiment 3) larvae. Larvae were stocked into replicate sets of four 10‐L aquaria with ambient 1‐μm filtered sea water (28 ± 1.5°C and 36 ppt) and cultured for four days at densities of 0.5, 2, 5, 7, or 10 larvae/mL and provided with microalgae rations at each of five densities (cells larvae^?1 day^?1); 0, 1, 3, 5, or 8 × 10³ (D‐veliger larvae, Experiment 1); 0, 5, 12, 18, or 25 × 10³ (umbonate larvae, Experiment 2); and 0, 15, 30, 40, or 60 × 10³ (eyed larvae, Experiment 3). Microalgae rations for each larval life stage were selected on the basis of increasing food requirement with larval size and comprised a 2:1:1 mixture of Chaetoceros calcitrans, Tisochrysis lutea, and Pavlova spp., calculated on an equal dry‐weight basis. Contour plots were generated from larval survival and larval size (dorso‐ventral measurement [DVM]) data to determine optimal culture conditions. Larvae showed high survival (54–100%) over a wide range of both treatment parameters across all life stages, confirming broad tolerance limits for this species. The interaction effects of larval stocking density and microalgae ration on larval size were significant (p < 0.001) across all life stages. Results indicate that maximum larval size (DVM) is achieved when S. echinata are cultured at: 6–8 larvae/mL and fed 5–6 × 10³ cells larvae^?1 day^?1 for D‐veligers (mean DVM >80 μm), at 2–8 larvae/mL and fed 11–25 × 10³ cells larvae^?1 day^?1 for umbonate larvae (mean DVM > 190 μm), and at 1–4 larvae/mL and fed 15–40 × 10³ cells larvae^?1 day^?1 for eyed larvae (mean DVM >230 μm). Results will help refine current hatchery methods for S. echinata supporting further development toward commercial aquaculture production of this species.     

Studies on triploid oysters in Australia: Evaluation of cytochalasin B and 6-dimethylaminopurine for triploidy induction in Sydney rock oysters Saccostrea commercialis (Iredale and Roughley)

Naturally spawned Sydney rock oysters Saccostrea commercialis (Iredale and Roughley),were used to determine the appropriate stage of development for inducing triploidy and to compare the effectiveness of cytochalasin B (CB) and 6-dimethylaminopurine (6-DMAP) in dose-optimization trials. Induction should commence at 50% first polar body (PB1) extrusion in eggs (approximately 17-19 min post-fertilization at 25^oC). By day 5 the highest triploidy percentage and yield (number of triploid larvae per 100 fertilized eggs) were achieved in the ranges of 0.75-1.5 mg CB 1^-1 (1.6-3.1 μm CB)or 200-400 μm 6-DMAP (32.6-65.3 mg 6-DMAP l^-1). However, CB treatment resulted in greater survival and triploidy percentage than 6-DMAP in Sydney rock oysters.     

Amazon River water in the northeastern Caribbean Sea and its effect on larval reef fish assemblages during April 2009

During April to June 2009, a large bolus of Amazon River water impacted the northeastern Caribbean Sea. Shipboard observations collected near Saba Bank, the U.S. and British Virgin Islands, and the Anegada Passage showed low surface salinity (35.76 ± 0.05 Practical Salinity Unit (PSU)), elevated surface temperature (26.77 ± 0.14°C), high chlorophyll‐a (1.26 ± 0.21 mg m^?3) and high dissolved oxygen (4.90 ± 0.06 mL L^?1) in a 20‐ to 30‐m thick surface layer in the riverine plume. The water was ~1°C warmer, 1 PSU fresher, 0.3 mL L^?1 higher in oxygen and 1.2 mg m^?3 higher in chlorophyll‐a than Atlantic Ocean waters to the north, with Caribbean surface waters showing intermediate values. Plankton net tows obtained in the upper 100 m of the water column revealed larval fish assemblages within the plume that were significantly different from those of the surrounding waters and from those encountered in the area in previous years. The plume waters contained higher concentrations of mesopelagic fish larvae from the families Myctophidae and Nomeidae, which as adults typically inhabit offshore, deep water habitats. Concentrations of larvae from inshore and reef‐associated families such as Scaridae, Serranidae, Labridae and Clupeidae were lower than those found outside the plume in similar shallow areas, particularly in near‐surface waters. An event like the one observed in 2009 had not been documented in at least the past 30 yr, and yet it was followed by another similarly extreme event in 2010. The ecological implications, including any long‐term consequences of such recent extreme events, are important and merit further study.     

Plankton composition and biomass development: a seasonal study of a semi‐intensive outdoor system for rearing of turbot

Plankton food web dynamics were studied during a complete production season in a semi‐intensive land‐based facility for rearing of turbot (Scophthalmus maximus) larvae. The production season was divided into three production cycles of 3–5 weeks. Phytoplankton biomass (using chlorophyll a as biomass proxy) peaked in each production cycle. However, the maximum biomass decreased from spring (18 μg chlorophyll a L^?1) to fall (ca. 7 μg chlorophyll a L^?1), simultaneous with a decline in the concentration of dissolved nitrogen in the inoculating water. During the three production cycles, we observed decreasing copepod nauplii concentration from spring to fall in the rearing tanks. The decreasing nitrogen gave increasing carbon to chlorophyll a ratio in the seston (from 23 in spring to 73 in fall). The pool of free amino acids in seston was constant. We suggest that the decreasing nitrogen input in the inoculating water reduces the quality of the phytoplankton and thus the growth potential of the prey for fish larvae, copepods.     

Embryonic development and larval and post‐larval growth of the tropical scallop Nodipecten (= Lyropecten) nodosus (L. 1758) (Mollusca: Pectinidae)

This work describes for the first time the embryonic development of the tropical scallop Nodipecten nodosus. Larval and post‐larval growth parameters and some characteristics of larvae shell morphology were also ascertained. The larvae were obtained from the induced spawning of a group of broodstocks under controlled laboratory conditions. After fertilization, larval cultivation was carried out in conical tanks at a temperature of 26–27 °C. Larval density was controlled as a function of larval growth to give 10, 5 and 3 larvae mL^?1 from days 1, 3 and 8 respectively. The larvae were nourished with a 1:1 mix of Isochrysis galbana (clone T‐ISO) and Chaetoceros gracilis in portions varying between 30 000 and 70 000 cells mL^?1. Expulsion of polar groups was observed 5 and 15 min after fertilization, whereas the first cellular division occurred after 30 min. The first gastrule ciliates and trocophore larvae were noted after 8 and 18 h had elapsed, respectively, whereas prodissoconch I, or D‐larvae, were discerned after 26 h. Subsequently, larvae with prodissoconch II or veliger‐conch appeared at 30 h. Larval development continued for 10–12 days, followed by metamorphosis, at an approximate length of 208–230 µm. The growth of the post‐larvae was evaluated for 9 days. Larval and post‐larval growth corresponded to the linear equations L = 71.85 + 10.85t, r² = 0.99, and L = 44.09 + 17.81t, r² = 0.94 respectively. Accordingly, larval morphology and size disparities are discussed with respect to other tropical pectinids.     

Digestive enzyme activity at different developmental stages of blackspot seabream, Pagellus bogaraveo (Brunnich 1768)

Blackspot seabream, Pagellus bogaraveo (Brunnich), has been identified as a potential species to diversify European aquaculture production. Although rearing aspects have been widely investigated, little information exists on the nutritional requirements for this species. The aim of this study was to build up information on the activity of digestive enzymes at certain developmental stages of blackspot seabream in order to understand the nutritional needs of larvae and post larvae. Fish larvae were reared from hatching to 55 days after hatching (dah), and the feeding plan consisted in rotifers (5–35 dah), Artemia naupli (30–35 dah) metanaupli (35–45) and Gemma microdiet (45–55 dah). At 7, 11, 21, 45 and 55 days after hatching (dah), pooled samples of fish larvae were collected for analysis of trypsin, amylase, lipase, alkaline phosphatase and leucine–alanine peptidase activity. Up to 21 dah, the whole larvae body was used for enzymatic analysis, whereas in older larvae only the dissected abdominal cavity was used. Blackspot seabream body dry weight growth was exponential, increasing from 60 μg at 5 dah to 30±9.7 mg at 55 dah. Amylase specific activity decreased significantly during development, exhibiting at 11 dah (0.6 U mg^?1 protein) an average value 2.7 times lower than at 7 dah, and remaining stable between 45 and 55 dah (0.7 U mg protein^?1). Trypsin specific activity remained constant until 21 dah (between 38 and 44 mU mg protein^?1), which could be related to the larvae feeding regime. At later stages of development, lipase‐specific activity exhibited a significant increase (P<0.05), being three times higher at 55 dah (8 U mg protein^?1) than at 45 dah. The total activity of the studied digestive enzymes increased significantly during larval development (until 21 dah), whereas afterwards only lipase and leucine–alanine peptidase increased significantly between 45 and 55 dah. The pattern of digestive enzymes activity was related to organogenesis and the type of food used at different developmental stages.     

A study of spring-and autumn-spawned herring (Clupea harengus L.) larvae in the Norwegian Coastal Current during spring 1990

An intensive sampling program for yolk-sac herring larvae and microzooplankton was carried out in the main spawning area of Norwegian spring-spawning herring during March to April 1990 (between 62^o and 63^o30'N) to estimate their hatching period and the abundance of copepod eggs and nauplii. Additional investigations were carried out in the Skagerrak area during January-March and on the Norwegian Shelf in May to study the otolith microstructure of the herring larvae. In May both autumn- and spring-spawned herring larvae were found in the samples from the Norwegian Shelf. They were easily distinguished by differences in otolith microstructure. The pattern in increment widths in the otoliths of the autumn-spawned larvae indicated that these larvae had not been transported through the Skagerrak area, but more likely were carried directly from the northern North Sea across the Norwegian Trench and into the Norwegian Coastal Current system. The calculated hatching of the spring-spawned larvae sampled in May occurred significantly later than the observed hatching over the spawning grounds. The results suggest a mismatch between the abundance of first-feeding herring larvae and their prey organisms, resulting in a higher survival of those herring larvae hatching during the latest part of the spawning period. This coincides with a general increase towards the middle of April in the abundance of prey organisms, from 1 to 4 1^_1. There were no differences in otolith microstructure among spring-spawned herring larvae sampled on the shelf in May, indicating that these larvae originated from the same cohort and were well mixed throughout the whole shelf area.     

Effects of single and combined microalgae on larval growth, development and survival of the commercial sea cucumber Holothuria spinifera Theel

The results of the study on the suitable algal feed for the mass rearing of holothurian larvae through hatchery system are presented. Auricularia larvae, after 48 h of fertilization, obtained from induced spawning of Holothuria spinifera, were fed with different algae Isochrysis galbana, Nanochloropsis salina, Pavlova lutheri, Tetraselmis chuii and Chaetoceros calcitrans as well as I. galbana+C. calcitrans to ascertain the effect of single and combined microalgal diet. The rate of feeding was 2 × 10⁴ cells larvae^–1 day^–1 for a period of 9–12 days. The growth rate of 59 μm day⁻¹ with 90% and 43 μm day⁻¹ with 100% occurrence of late auricularia in the larvae fed with C. calcitrans alone and I. galbana+C. calcitrans, respectively, indicated that C.calcitrans itself or in combination with I. galbana is the effective feed for the larvae of H. spinifera.     

Turbulent mixing and mesoscale distributions of late-stage fish larvae on the NW Shelf of Western Australia

Light traps were deployed to describe vertical and cross‐shelf distributions of late‐stage larval fishes during five cruises in each of the 1997/98 and 1998/99 summers in the region of the Gulf of Exmouth on the southern North West Shelf of Western Australia. At each light trap station on a cross‐shelf transect we measured water temperature, salinity and chlorophyll a and used vertical plankton tows to estimate zooplankton biomass and copepod abundance. Current meters were deployed on moorings near the transect and the data used to model flows and mixing on the NW Shelf and in the Gulf. The majority of reef, pelagic and baitfish larvae (81, 83 and 66% respectively) were collected at only two stations that marked the boundary between stratified waters offshore and well‐mixed water within the Gulf. Most baitfishes (primarily Spratelloides spp.) were captured by traps deployed near the seabed, while reef fishes (mostly pomacentrids, lethrinids and siganids) and pelagic species (mostly scombrids and carangids) were captured in traps deployed near surface. Catch composition varied between summers with 64% of baitfishes collected in the first summer, while the majority of reef and pelagic fishes (81 and 80% respectively) were captured in the second summer. Modelling of circulation showed that the velocity of tidal currents was enhanced by constriction of flow between NW Cape and South Muiron Island and by shallowing of the shelf. Flood‐tide intrusions of water allowed the thermocline to move up the continental shelf, upwelling cool nutrient‐rich water that was then mixed throughout the entire water column at stations in the mouth of the Gulf. This upwelling and mixing resulted in higher chlorophyll a concentrations and copepod abundances either as a result of local in situ growth or advection/aggregation processes, and may account for the great abundances of late‐stage fish larvae in the mouth of the Gulf.     

Larval development and salinity tolerance of Japanese flounder (Paralichthys olivaceus) from hatching to juvenile settlement

Salinity tolerance and growth of Japanese flounder Paralichthys olivaceus at different developmental stages were evaluated, including newly hatched larvae (nhl), yolk sac larvae (ysl), oil droplet larvae (odl), post oil droplet larvae (podl), premetamorphic larvae (preml) and prometamorphic larvae (proml), at 11 salinities from 5 to 55 g L^?1 for 96 h. The ontogenesis during the early life of P. olivaceus was investigated under hatchery salinity 35 g L^?1. The results showed that suitable salinities for nhl, ysl, odl, podl, preml and proml larvae were 10 to 25 g L^?1, 10 to 30 g L^?1, 20 to 30 g L^?1, 30 g L^?1, 10 to 30 g L^?1, 15 g L^?1, respectively, demonstrating an ontogenetic variation of salinity tolerance. The salinity tolerance of nhl, ysl, preml was higher than that of odl, podl and proml. The ysl and preml larvae displayed wide salinity tolerances. The present findings demonstrate that the suitable salinity for larviculture of P. olivaceus is 20–25 g L^?1 before the depletion of oil droplet; after that, higher salinity (30 g L^?1) should be ensured for the post‐oil droplet larvae; the premetamorphic larvae can be cultured at a wide salinity range (10–30 g L^?1), and the metamorphosed larvae should be reared at salinity about 15 g L^?1.     

Improved techniques for rearing mud crab Scylla paramamosain (Estampador 1949) larvae

A series of rearing trials in small 1 L cones and large tanks of 30–100 L were carried out to develop optimal rearing techniques for mud crab (Scylla paramamosain) larvae. Using water exchange (discontinuous partial water renewal or continuous treatment through biofiltration) and micro‐algae (Chlorella or Chaetoceros) supplementation (daily supplementation at 0.1–0.2 million cells mL⁻¹ or maintenance at 1–2 millions cells mL⁻¹), six different types of rearing systems were tried. The combination of a green‐water batch system for early stages and a recirculating system with micro‐algae supplementation for later stages resulted in the best overall performance of the crab larvae. No clear effects of crab stocking density (50–200 larvae L⁻¹) and rotifer (30–60 rotifers mL⁻¹) and Artemia density (10–20 L⁻¹) were observed. A stocking density of 100–150 zoea 1 (Z1) L⁻¹, combined with rotifer of 30–45 mL⁻¹ for early stages and Artemia feeding at 10–15 nauplii mL⁻¹ for Z3–Z5 seemed to produce the best performance of S. paramamosain larvae. Optimal rations for crab larvae should, however, be adjusted depending on the species, larval stage, larval status, prey size, rearing system and techniques. A practical feeding schedule could be to increase live food density from 30 to 45 rotifers mL⁻¹ from Z1 to Z2 and increase the number of Artemia nauplii mL⁻¹ from 10 to 15 from Z3 to Z5. Bacterial disease remains one of the key factors underlying the high mortality in the zoea stages. Further research to develop safe prophylactic treatments is therefore warranted. Combined with proper live food enrichment techniques, application of these findings has sustained a survival rate from Z1 to crab 1–2 stages in large rearing tanks of 10–15% (maximum 30%).     

Distribution patterns of larval myctophid fish assemblages in the subtropical–tropical waters of the western North Pacific

We examined larval myctophid fish assemblages and their distribution patterns, based on discrete depth sampling. Samples were collected at 19 stations along a transect that crossed the subtropical–tropical waters of the western North Pacific. In total, we collected 27 189 larvae of 40 myctophid species or types, belonging to 15 genera. Three assemblages were recognized, based on their species composition: Kuroshio Axis (KuA), Kuroshio Countercurrent (KCC), and Subtropical Countercurrent–North Equatorial Current (SCC–NEC) assemblages. The distributions of these assemblages were well defined by the positions of the KuA and the Subtropical Convergence. Each species had a specific distribution depth, and none showed diel vertical migration. Larvae of the subfamily Lampanyctinae were distributed in shallower waters (0–50 m) than larvae of the subfamily Myctophinae (50–150 m). Larvae of the same species were distributed at lower depths in the SCC–NEC area than in the KCC area. This corresponded to the abundance of chlorophyll a, which would reflect abundance of prey organisms such as copepod nauplii and copepodites.