Survival Of Fish Larvae Research Articles

Unraveling the ecological impacts of alewife in a large Midwest reservoir decades after introduction

Alewives Alosa pseudoharengus are native to the Atlantic Coast but have been introduced to inland waters as forage for sportfish populations. Alewife introductions have benefitted sportfish growth and body condition but have also negatively influenced larval fish survival through predation or competition for zooplankton. In 1986, alewives were stocked into Lake McConaughy, Nebraska, and became abundant and self-sustaining shortly thereafter. It has since been hypothesized that the alewife introduction altered zooplankton size and species composition and potentially negatively influenced Walleye recruitment. However, no studies on alewife distribution or food habits have been conducted on Lake McConaughy to date to investigate the potential influences of alewife on the fish and zooplankton communities. We collected alewives in the nearshore areas of Lake McConaughy during May–July 2022 and 2023 using short-term (about 1 h) small mesh horizontal gill net sets. We spatially assessed alewives by sampling the north and side south sides in addition to four classified quadrants of the reservoir. Total lengths (mm) were recorded, and stomachs were collected from up to 20 alewife per net. Prey were identified and food habits were summarized as percent composition by number. Zooplankton consumption was also paired with vertical Wisconsin zooplankton net tows taken at each site to assess prey selectivity. There was no evidence of piscivory suggesting that alewife predation is not influencing fish recruitment in Lake McConaughy. Alewives almost exclusively consumed zooplankton throughout the study period, suggesting the potential for interspecific competition with young-of-year fish. Our research provides a greater understanding of how introducing a non-native prey species to benefit sport fishes may have unintended negative consequences.

Larval Lake Whitefish (Coregonus clupeaformis) zooplankton consumption remains constant despite variation in prey densities in western Lake Erie

Abstract Larval fish growth and survival could be limited or reduced due to patchiness of zooplankton densities, even in productive aquatic systems. Recent declines in Lake Whitefish (Coregonus clupeaformis) populations prompted research to identify underlying mechanisms controlling survival at early life stages. In Lake Erie, the bottleneck window controlling year-class strength of Lake Whitefish likely occurs during the first growing season, suggesting that availability of important prey could influence year-class strength. Therefore, spatial and temporal larval Lake Whitefish distribution, diet, and prey utilization were evaluated in western Lake Erie. The pelagic Lake Whitefish larval period in the western basin extends from April 1 to May 15 with most larvae concentrated nearshore at the surface both day and night. Cyclopoid copepods were the most important prey item; however, calanoid copepods and Cladocera were consistently consumed, indicating that copepods and Cladocera were important larval Lake Whitefish prey items. Copepod and Cladocera biomass were the highest nearshore, overlapping with the highest larval Lake Whitefish densities. However, the amount of food consumed by larvae was consistent in all areas, suggesting that offshore areas in western Lake Erie with relatively low zooplankton biomass harbor enough food to satiate larval Lake Whitefish. Therefore, it is unlikely that prey availability limits survival through means of starvation during the larval phase.

Annual, seasonal and spatial differences in the growth rate of Baltic cod larvae and early juveniles in relation to zooplankton biomass fluctuations in 2006-2014

It is an acknowledged theory that a faster growth rate, determined by various environmental drivers, may boost the survival of larval and juvenile fish. In this study we examined the differences in the growth rate of larval and juvenile cod (age 2 – 136 d; SL: 4.1 – 39.2 mm) between the years 2006 and 2014, sub-areas of the Baltic Sea (Bornholm Basin, BB; Słupsk Furrow, SF; Gdańsk Basin, GB), and seasons (spring and summer). The average growth rate for all specimens was 0.25 mm/d, with significantly lower values between 2012 and 2014 than between 2006 and 2011. A reduction in zooplankton biomass, especially the large zooplankton fraction, was observed after the 2006–2008 period, which was related to the prevailing temperature conditions in the surface layers. The reduction in zooplankton biomass was accompanied by changes in the structure of zooplankton: less T. longicornis, C. hamatus, and Pseudocalanus spp., and more Acartia spp. The results suggest that the inter-annual differences observed in zooplankton biomass and structure are likely responsible for the observed reduction in the growth rate of cod larvae between 2012 and 2014 compared to the years between 2006 and 2011. The growth rate reduction could be one of the reasons for the decline in the recruitment of eastern Baltic cod between the years 2013 and 2015, after the high recruitment years of the period 2011-2012.

Review of Central-Eastern European Propagation and Larvae Nursing Method for Common Carp (Cyprinus carpio L.).

Common carp (Cyprinus carpio L.) as a cultivated fish species has huge importance all over the world. According to FAO statistics, carp is the third most widely bred freshwater pond fish species; only two other Cyprinids (silver carp and grass carp) are bred in higher amounts. Carp is native all over Asia and in a large part of Europe. As a result of human intervention, at present, carp are widespread all over the world, except for the Arctic region. Carp breeding was launched in the antique period, in the ancient Chinese Empire and the Roman Empire. The presently applied method of breeding of common carp has a long evolution. From the effectiveness point of view, the propagation and early-life nursing are crucial parts of carp production, as they provide seed stocks for the further growing section. Without effective propagation, there is no intensive carp production. Nowadays, more advanced propagation methods are available all over the world; however, in the current review, only the main milestones and production efficiency of the propagation and nursing method used in the ponds of Eastern Central Europe are discussed. In the historical overview of carp reproduction, first the natural reproduction, then the semi-extensive and intensive hatchery propagation are presented and investigated in detail. The analysis focuses on the advantages and disadvantages of the method. In particular, the different important milestones of the advanced hatchery method are shown and explained. The effectiveness is proven even with practical calculations. Not only the reproduction, but the pond nursing method is also presented and discussed, concentrating on the management of evolutionarily adapted natural feeds (Zooplankton) and their effect on the survival of fish larvae.

Highly structured habitats mitigate size‐ and growth‐selective mortality of post‐settlement juvenile fish

AbstractThe role of vegetated habitats such as seagrass and macroalgal beds as nurseries is essential for the survival of larval and juvenile fish, although quantitative evaluation of the contribution of these habitats to nursery function is limited. Moreover, growth–survival relationships of larvae and juveniles associated with vegetated habitats have rarely been examined. To quantitatively and qualitatively evaluate the processes affecting juvenile survival in vegetated habitats, we investigated whether there is a correlation between the degree of selection for bigger and faster‐growing fish and mortality rates for three cohorts by birth date of post‐settlement black rockfish (Sebastes cheni) in a macroalgal bed. We also analyzed relationships between growth rate and experienced temperature by age class to examine the effects of temperature on growth. The latest cohort, which grew under lower vegetation coverage due to a seasonal increase in water temperature, showed higher mortality with evidence of strong selection for survival of bigger and faster‐growing fish. The growth–temperature relationships showed that positive effects of temperature on growth weakened after settlement. Therefore, we suggest that macroalgal coverage has a critical role in controlling the growth–mortality relationship of post‐settlement S. cheni. Furthermore, the negative effects of high temperature on juvenile survival through loss of vegetation may be greater than the positive effects on juvenile growth. These findings would contribute to the management of fisheries resources by increasing the understanding of relationships between survival mechanisms in fish early life stages and vegetation phenology of their habitat under the increasing effects of global warming.

Eggs Hatching of Betta Fish (Betta splendens) with The Addition of Ketapang Leaves (Terminalia cattapa Linn) at UPR Mitra Mina Sejahtera Indralaya, Ogan Ilir District

The limited number of fish seeds is still an obstacle in betta fish cultivation activities due to the low percentage of hatching and high mortality of larvae. This research aims to increase the percentage of egg hatching and survival of betta fish by stimulating ketapang leaves. This research was carried out in a controlled area at UPR Mitra Mina Sejahtera located in Griya Sejahtera Indralaya Housing, Ogan Ilir Regency from June to July 2022. The addition of ketapang leaves as much as 2 g per L (P2) can increase the hatching percentage at 96.97% and betta fish larval survival rate to 87.92%. The water quality obtained from this research is the temperature of P1 ranges from 26.4-27.3°C, P2 ranges from 26.7-27.2, control ranges from 26.5-27.1°C, pH P1 ranges from 6.5-6.9, P2 ranges from 6.5-6.7 and control ranges from 6.9-7.2 and dissolved oxygen P1 ranges from 1.03-1.09 mg per L, P2 ranges from 1.00-1.05 mg per L and control ranged from 1.04-1.10 mg per L.

Variation in Prairie Chub hatch relationships across wet and dry years in the upper Red River basin

AbstractObjectiveThe Prairie Chub Macrhybopsis australis is a poorly studied minnow species endemic to the upper Red River basin and is of both state and federal conservation interest due to uncertainty about its life history and potential listing status. The upper Red River basin of Oklahoma and Texas is a harsh environment where drought and extreme flow events are exacerbated by human alterations. As an assumed pelagic‐broadcast‐spawning minnow, the Prairie Chub is capable of a protracted spawning season and larval fish survival is assumed to be linked to discharge and streamflow variability.MethodsWe systematically collected 2,017 age‐0 Prairie Chub from seven sites (North Fork Red River, Salt Fork Red River, Pease River, Red River, Prairie Dog Town Fork Red River, North Wichita River, and South Wichita River) with variable flow patterns during April–September 2019 and May–August 2020. We used otolith age estimates and back calculations to determine successful spawning dates. We used a hurdle model framework to examine relationships between hatch probability and hatch frequency.ResultHatch probability had a negative relationship with calendar day and declined as calendar day increased. Hatch counts peaked in late June and early July and declined thereafter in 2019 but showed no discernible peak during the spawning season in 2020. Hatch probability during the spawning season increased with relative flow and air temperature. Increased hatch counts were also positively related to discharge variability (CV) for the 10 d prior to hatch dates.ConclusionOur findings indicated that successful hatches had considerable spatial and temporal variability, with some sites contributing minimally to the population during some years. Spatial and temporal variability of hatch probability and hatch frequencies pose a variety of considerations for future conservation and management efforts, particularly given the pending federal listing status of the species.

EFEKTIVITAS PEMBERIAN PHOTOPERIOD YANG BERBEDA PADA MEDIA PEMELIHARAAN LARVA IKAN PAPUYU (Anabas testudineus) TERHADAP LAJU PERTUMBUHAN DAN KELANGSUNGAN HIDUP

The purpose of this study was to determine which photoperiod affects the growth and survival of papuyu (Anabas testudineus) larvae. The research was conducted on Jl. Dr. Wahidin Sudiro Husodo Kuala Pembuang I for 6 weeks. The larvae used in this study were 3 days old with a stocking density of 20 fish/tub, the larvae were reared with different lighting durations for 27 days. The lighting treatment was carried out using lights installed in each treatment equipped with a switch with a power of 5 watts, then each aquarium was given black plastic so that the light effect from other treatment lamps did not affect other aquariums. Feeding was carried out by means of satiation feeding with the type of fengli flour feed size 0. This study used 4 treatments and 3 replications, namely treatment A: 24T:0G, B: 16T:8G, C: 8T: 16G and D: 0T: 24G. Research parameters include larval growth and fish survival and water quality as supporting data. Based on the results of the study, a good photoperiod for growth rate and survival is 24 hours of light, 0 dark. While the results of the analysis of giving different photoperiods to papuyu fish larvae had no effect on absolute weight growth but on length growth showed a very real effect, while for the survival of fish larvae there was no effect on the treatment.

Review on n-3 HUFA and Live Food Organism for Marine Fish Larvae Nutrition

Marine fish farm industries face ongoing challenges due to a lack of quality seed, a low survival rate and a slow growth rate of marine fish larvae. One of the most sensitive problems is a nutritionally balanced quality feed for rearing these larval fish at the first feeding stage. Many studies have reported high requirements of n-3 highly unsaturated fatty acids, mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for proper development, which have also been reported to increase the survival and growth status of larval fish. Marine fish larvae have difficulties accepting artificial feed at their weaning stage, so live food plays a vital role in the rearing process. Artemia is one of the most commonly used live food organisms in marine fish larvae production systems. However, they are deficient in EPA and DHA, which are most critical for larval development. Recent advancements in live food production systems have developed several techniques of bio-encapsulation and enrichment of nutrients in live food. But the instability of DHA and the high cost of enrichment procedures remain-bottlenecks for supplying proper nutrients through live food. This short review emphasizes challenges in marine fish larvae culture in terms of HUFAs nutrition with a comparative study on DHA requirements of marine larval fish and its availability in live food organism Artemia. We also highlighted several factors affecting DHA enrichment process and its degradation following enrichment procedures.

Optimum level of lipid in granulated microdiets for rockfish (Sebastes schlegeli) larvae

Lipid is one of the most important nutritional factors affecting growth and survival of larval fish. This study aims to determine optimum level of lipid in formulated microdiets for the 10-day old rockfish (Sebastes schlegeli) larvae. Five granulated microdiets (CL11, CL14, CL17, CL20, and CL23) containing various (11%, 14%, 17%, 20%, and 23%, respectively) levels of lipid were prepared, and their lipid levels were controlled by adding fish oil at the expense of dextrin. The effects of feeding rockfish larvae with these formulated microdiets were compared with two commercial microdiets (Belgium and Japan), and local crumble diet. At the end of the 29-day feeding trial, weight gain (%) and total length (mm) of larval fish fed the CL20 diet were significantly (P < 0.0001 for both) greater and longer than those of larval fish fed all other formulated (CL11, CL14, CL17, and CL23) microdiets, and crumble diet. The proximate composition of the whole-body fish, except for lipid content was not significantly (P > 0.05) affected by the experimental diets. Crude lipid content of the whole-body fish was relatively well reflected from lipid levels of the experimental diets. In conclusion, the greatest weight gain and longest total length were obtained in larval fish fed the CL20 diet among the experimentally formulated microdiets. The optimum lipid level in the experimentally formulated microdiet was estimated to be 17.3% for rockfish larvae based on the broken-line analysis.

Energy use, growth and survival of coral reef snapper larvae reared at elevated temperatures

The success of individuals during the pelagic larval phase is critical to maintaining healthy and viable populations of coral reef fishes; however, it is also the most environmentally sensitive and energetically demanding life stage. Climate change is increasing the frequency and intensity of marine heatwaves, which could have significant effects on the development and survival of larval coral reef fishes. However, little is known about how the larvae of pelagic-spawning coral reef fishes will be affected due to the difficulty of spawning and rearing these species in captivity. In this study, we tested how elevated temperatures, similar to those occurring during a marine heatwave, affected the yolk utilization, growth, and survival of larval, Lutjanus carponotatus, a common mesopredatory fish on Indo-west Pacific coral reefs. Eggs and larvae were reared at a current-day average summer temperature (28.5 °C) and two elevated temperatures (30 °C and 31.5 °C) until 14 d post-hatch (dph). Larvae in the elevated temperatures depleted their yolk reserves 39% faster than at the control temperature. The standard length of larvae was 55% (30 °C) and 92% (31.5 °C) longer in the elevated temperature treatments than the control temperature at 14 dph. Conversely, survival of larvae was 54% (30 °C) and 68% (31.5 °C) lower at elevated temperatures compared with the control temperature. This study provides new insights as to how the early life stages of coral reef fishes could be affected by ocean warming and marine heatwaves, with implications for their population dynamics.

Evaluation of the Optimal Protein Required in Granulated Microdiets for Rockfish (Sebastes schlegeli) Larvae.

Protein is an essential nutrient that supports fish growth, and the inadequacy in formulating their diets with an optimum protein level can deteriorate their growth performance. The protein requirement in granulated microdiets was estimated for rockfish (Sebastes schlegeli) larvae. Five granulated microdiets (CP42, CP46, CP50, CP54, and CP58) containing 42% to 58% crude protein levels with a 4% increment at a constant gross energy level (18.4 kJ/g diets) were prepared. The formulated microdiets were also compared with imported microdiets, Inve (IV) and love larva (LL) from Belgium and Japan, respectively, and a locally marketed feed (crumble). At the cessation of the study, the survival of larval fish was not different (P > 0.05), but the weight gain (%) of fish fed the CP54, IV, and LL diets was significantly (P < 0.0001) higher than that of larval fish fed the CP58, CP50, CP46, and CP42 diets. The crumble diet achieved the poorest weight gain of larval fish. Furthermore, the total length of rockfish larvae fed the IV and LL diets was significantly (P < 0.0001) longer than that of the fish fed all other diets. The chemical composition of the fish's whole body, except for ash content, was not influenced by the experimental diets. The experimental diets affected essential amino acid profiles, such as histidine, leucine, and threonine, and nonessential amino acid profiles, such as alanine, glutamic acid, and proline of the whole body of larval fish. Conclusively, based on the broken line analysis of weight gain of larval rockfish, protein requirement in granulated microdiets was estimated to be 54.0%.

First feed matters: The first diet of larval fish programmes growth, survival, and metabolism of larval ballan wrasse (Labrus bergylta)

The use of cleaner fish, such as the ballan wrasse (Labrus bergylta), is important for combatting the sea lice problem in salmonid cage farming. Ballan wrasse is the only wrasse species that is cultivated, though only about 50% of the approx. 3 million ballan wrasse used in 2020 was produced by aquaculture. The major obstacle for large scale cultivation of ballan wrasse is the difficult first feeding phase and a lack of functional feeding protocols.Like most pelagic marine fish larvae, ballan wrasse do not accept inert diets as first feed, and feeding regimes based on rotifers and Artemia (brine shrimps) usually lead to mixed results and are far from being optimal nutrition for the larvae.In a 48-day start feeding experiment, we studied the feasibility of replacing rotifers by an Experimental cirriped diet or copepod nauplii (Acartia tonsa) and replacing Artemia by nauplii of the cirriped Semibalanus balanoides. Later, all treatments received the same formulated diets. We sampled larvae at each feed transition to analyze different response variables such as growth, morphometry, gene expression, lipidomics, histology, and microbiology.We found significant differences in survival rates and growth. Larvae fed copepods as the first diet had significantly higher survival rates than larvae start-fed on either rotifers or small experimental cirripeds, and this pattern was also reflected in early growth and bone development. Gut histology at the end of the experiment (48 days after hatching) showed a more developed intestinal tissue in the larval group fed copepods first and cirripeds as the second diet compared to the other larval groups.Gene expression at day 48 post hatch still revealed pronounced differences between the larval group first fed on rotifers and larvae from the other three feeding regimes which received natural, unenriched diets. Even weeks after receiving the same formulated diets, lipidomics analyses revealed that several lipid species correlated either negatively or positively with larval growth rates or mortality.Our results are a clear indication for nutritional programming, pointing towards the importance the first diet has for the further life of a fish.

The Effects of the Harmful Algal Bloom Species Karenia brevis on Survival of Red Porgy (Pagrus pagrus) Larvae.

The harmful algal bloom species, Karenia brevis, forms annual, often intense blooms in the Gulf of Mexico, particularly along the west Florida shelf. Though the ability of K. brevis blooms to cause mass mortalities in juvenile fish are well documented, the direct effect of bloom concentrations on larval fish has not been studied extensively. To better understand the potential effect of K. brevis on larval fish survival, laboratory spawned red porgy (Pagrus pagrus) larvae from 4–26 days post-hatch were exposed to concentrations of K. brevis observed in the field for either 24 or 48 h. This species is representative of fish which spawn in regions of the Gulf of Mexico and whose larvae are epipelagic and may encounter K. brevis blooms. In this study, three different K. brevis strains varying in the amount of brevetoxin produced were tested. Larval survivorship was found to be inversely proportional to the amount of brevetoxin produced by each strain. The EC50 value from the combined 24 h experiments was ~163,000 K. brevis cells L−1, which corresponds to cell concentrations found in moderately dense blooms. Larval mortality also increased substantially in the 48 h versus 24 h exposure treatments. These findings indicate K. brevis blooms have the potential to contribute to natural mortality of fish larvae and further reduce inter-annual recruitment of fishery species whose stocks in the Gulf of Mexico may already be depleted.

Ocean Acidification Alters the Predator – Prey Relationship Between Hydrozoa and Fish Larvae

Anthropogenic CO2 emissions cause a drop in seawater pH and shift the inorganic carbon speciation. Collectively, the term ocean acidification (OA) summarizes these changes. Few studies have examined OA effects on predatory plankton, e.g. Hydrozoa and fish larvae as well as their interaction in complex natural communities. Because Hydrozoa can seriously compete with and prey on other higher-level predators such as fish, changes in their abundances may have significant consequences for marine food webs and ecosystem services. To investigate the interaction between Hydrozoa and fish larvae influenced by OA, we enclosed a natural plankton community in Raunefjord, Norway, for 53 days in eight ≈ 58 m³ pelagic mesocosms. CO2 levels in four mesocosms were increased to ≈ 2000 µatm pCO2, whereas the other four served as untreated controls. We studied OA-induced changes at the top of the food web by following ≈2000 larvae of Atlantic herring (Clupea harengus) hatched inside each mesocosm during the first week of the experiment, and a Hydrozoa population that had already established inside the mesocosms. Under OA, we detected 20% higher abundance of hydromedusae staged jellyfish, but 25% lower biomass. At the same time, survival rates of Atlantic herring larvae were higher under OA (control pCO2: 0.1%, high pCO2: 1.7%) in the final phase of the study. These results indicate that a decrease in predation pressure shortly after hatch likely shaped higher herring larvae survival, when hydromedusae abundance was lower in the OA treatment compared to control conditions. We conclude that indirect food-web mediated OA effects drove the observed changes in the Hydrozoa – fish relationship, based on significant changes in the phyto-, micro-, and mesoplankton community under high pCO2. Ultimately, the observed immediate consequences of these changes for fish larvae survival and the balance of the Hydrozoa – fish larvae predator – prey relationship has important implications for the functioning of oceanic food webs.

Effects of formulated microdiets on weaning success and larval performance of pike silverside Chirostoma estor (Jordan, 1879)

High growth and survival of fish larvae are still milestones that many cultured species have to achieve. A primary limitation is the capacity of fish larvae to digest conventional microdiet ingredients in their short intestine agastric alimentary canals, making live feed indispensable and costly in most cases.Therefore, ad hoc formulation of microdiets taking into account the specific characteristics of an early digestive system may improve larvae growth and survival. For these, three trials were performed in pike silverside larvae to evaluate the minimum weaning time after a co-feeding period with live feed and a commercial microdiet; the performance of larvae fed formulated microdiets with different proportions of soluble proteins, and the effect of the best performing microdiet supplemented with different levels of probiotics on larvae growth and survival. Larvae weaned at 10 dph after a three day-period of co-feeding with live rotifers achieved similar performance to larvae exclusively fed with live rotifers. In terms of soluble protein proportions, only larvae fed the microdiet T2 containing 278 g soluble protein Kg−1 presented higher growth performance than a commercial microdiet (Otohime®). Finally, larvae fed the microdiet with 278 g soluble protein Kg−1 diet supplemented with the consortium L. acidophilus and L. plantarum (0.5/0.5%; 1.27 ×109 CFU g−1) presented the best performance, showing high potential as a total substitute for live feed in pike silverside larvae since 10 dph.

THE USE OF LIVE FOOD IN REARING OF THE LARVAE OF GRASS CARP CTENOPHARYGODON IDELLA

The larvae of grass carp Ctenophargodon idella were fed on three types of live food Brachionus calyciflorus, Artemia sp. and Daphnia magna. The study showed that live food is very important to achieve high growth and survival of fish larvae. The average weights of C. idella fed on B. calyciflorus were 118.12+3.0 mg / larvae and 29.48+0.8 mm / larvae respectively, and in case of Artemia sp. The rates were 103.13+1.5 mg/ larvae and 25.34+1.4 mm / larvae, while in the mixed food the rate were 122.80 + 1.8 mg / larvae and 30.08 + 1.1mm /larvae .The survival rate was better on B. calyciflorus treatment as it was 98.6 % ,while it was 98 % and 97% in case of mixed food and Artemia sp. Respectively .

Utilization of Live‐Food Enrichment with Polyunsaturated Fatty Acids (PUFA) for the Intensive Culture of Yellow Perch Larvae

AbstractChallenges associated with first feeding have impeded the intensive culture of larval Yellow Perch Perca flavescens. Live‐food enrichment with polyunsaturated fatty acids (PUFAs) can increase the growth and survival of larval fish, but this method has not been tested with Yellow Perch. This study includes two experiments that were meant to evaluate (1) the relative proportion of docosahexaenoic acid (DHA; 22:6[n‐3]) and arachidonic acid (ARA; 20:4[n‐6]) in enrichment emulsions and (2) the provision of PUFA emulsions in ethyl ester (EE) or triacylglycerol (TG) form on Yellow Perch growth and survival. Fish were provided with live rotifers Brachionus plicatilis and brine shrimp Artemia nauplii for the first 10 d of exogenous feeding within a specialized recirculating system (phase I). Fish were then transferred to flow‐through tanks and were fed Artemia nauplii for 3 d before gradually transitioning to a formulated starter diet (5–7 d; phase II). Fish size, growth, survival, swim bladder inflation rates, and lipid/fatty acid concentrations were evaluated after each phase. Overall, rotifers assimilated ARA in higher concentrations (23.3% of total fatty acids) than Artemia (0.6–0.7% of total fatty acids). Rotifers also tended to assimilate PUFAs better in EE form than in TG form (71.3% versus 66.5% Σn‐3 + n‐6 fatty acids). In the first experiment, fish from the ARA‐ and DHA‐enriched diet groups had greater swim bladder inflation rates (phase I) and growth rates (phase II) than the unenriched control group. In phase I of the second experiment, the EE enrichment group had a significantly faster growth rate than the TG enrichment group (specific growth rate: mean ± SD = 40.5 ± 0.9% and 36.6 ± 1.8%, respectively). Fatty acid composition of zooplankton was heavily influenced by enrichments, and fatty acid composition of larvae/juveniles reflected that of their live prey. The results of this study suggest that PUFA enrichment of live feeds can accelerate Yellow Perch growth and reduce the time spent in the critical period of early development.

Variation in larval Gulf Menhaden diet, growth and condition during an atypical winter freshwater-discharge event in the northern Gulf of Mexico

In January 2016, historic levels of rainfall in the upper Mississippi River Basin prompted the earliest opening of the Bonnet Carré Spillway, a water control structure on the Mississippi River that diverts flood-stage river water through an alternate pathway (Lake Pontchartrain) into the northern Gulf of Mexico. This unprecedented winter opening of the spillway coincided with the spawning season and larval ingress period for Gulf Menhaden, a forage fish species that supports the largest commercial fishery in the region. Oceanographic observations and plankton samples were collected in the Mississippi Bight region shortly after the Bonnet Carré Spillway winter opening to examine the impacts on larval Gulf Menhaden feeding, growth and condition. Three distinct water masses were identified based on temperature, salinity, and particle scattering (proxy for turbidity) characteristics. Larval Gulf Menhaden with the highest growth rates and body condition were collected in a water mass defined by relatively high temperature and salinity and relatively low turbidity and zooplankton (prey) abundance. In contrast, larvae with the slowest growth rates and poor body condition were collected in a water mass with the highest zooplankton abundance, but also highest turbidity and lowest temperature and salinity. This water mass was nearest the diversion outflow and most impacted by the spillway opening. Our results indicate that the anomalous freshwater discharge event resulted in hydrographic conditions that diminished otherwise favorable larval fish foraging habitat with abundant zooplankton prey. These findings suggest that the recent trend of Bonnet Carré Spillway openings may result in negative consequences for larval fish survival and subsequent fishery recruitment.

조도 및 광주기가 명태(Gadus chalcogrammus) 자어의 생존과 성장에 미치는 영향

This study investigated the survival rates and growth of larval walleye pollock (Gadus chalcogrammus) reared at different photomanipulation. Larval walleye pollock were reared at four light intensities (experiment 1: 50, 250, 1000 and 2500 lux) and five photoperiods (experiment 2: 24L:0D, 18L:6D, 12L:12D, 6L:18D and 0L:24D) from hatching (30 days post hatch). Survival of larval fish of experiment 1 was >15% and there was no significant difference between 50, 250, and 1000 lux, however, whole fish was dead at 16 days post hatch in 2500 lux. Growth of larvae at 1000 lux was greater than larvae at all other light intensities treatments. Survival rates of experiment 2 was >14% except for 0L:24D, and 18L:6D was significantly higher than that of larval fish reared at other photoperiods. In 0L:24D, the death occurred continuously after initial of experiment, whole larval fish died on 21 days post hatch. Growth of larvae that illuminated the light more than 12 hours were higher than that of larvae reared at 6L:18D. Considering these results, the optimal rearing light intensity and photoperiod was 1000 lux and 18L:6D, respectively. Further, intensive light or lightless condition cause mortality of walleye pollock larvae.