Juvenile Fish Research Articles

Fish predation on newly stocked juvenile predatory fish in a biomanipulated reservoir

Jůza T, Blabolil P, Čech M, Draštík V, Kubečka J, Muškaa M, Prchalováa M, Sajdlováa Z, Tušera M, Vašeka M, Vejříka L, Peterkaa J. 2024. Fish predation on newly stocked juvenile predatory fish in a biomanipulated reservoir. Lake Reserv Manag. 40:325–337. Juveniles of pikeperch, asp, and northern pike were stocked into the Římov Reservoir. Subsequently, potential fish predators were monitored by gillnets at the stocking sites and their diet was analyzed for presence of stocked fish. Asp and European perch were predominant predators, while pikeperch and northern pike were less abundant in gillnet catches. Digestive tract analysis revealed the highest percentage of ingested fish in northern pike, followed by pikeperch, asp, and European perch. The amount of stocked fish did not correlate with the number of predatory fish caught in gillnets. When asp was stocked, this species was strongly preferred by northern pike and partly by pikeperch and 0.3 individual of stocked asp was eaten per 1 kg of predatory fish captured by gillnets. During the northern pike stocking, this species was mainly preyed upon by asp and occasionally by northern pike, and 0.8 individual of stocked northern pike was eaten per 1 kg of predatory fish. When pikeperch was stocked, it was strongly preferred by pikeperch, northern pike, and European perch, it was almost absent in the diet of asp, and 1.1 individual of stocked pikeperch was eaten per 1 kg of predators. Our results indicate that pikeperch juveniles had the highest mortality rate due to predation after stocking, mainly due to sedentary behavior and the high proportion of cannibalism. In northern pike, cannibalism was found in only one case, and was never found in asp, which was under the lowest predation pressure.

Comparative studies on composition of feed additives for juvenile fish produced with bioconversion of fish raw materials

Technology of feed additive for fry feeding in fish farms is developed to provide both important nutrients (proteins, lipids, etc.) and optimal peptide composition of protein that is achieved using proteolysis of raw materials under certain conditions. For this purpose, enzymatic hydrolysis of substandard small-sized frozen pollock was used. The rational duration of the hydrolysis process was 60 min. that provided the degree of protein hydrolysis of 26–28 %. The experimental fermentolysate was concentrated to a water content of 3–4 % and presented as a feed additive TINRO-60. This product is compared with other feed additives (dried fermentolysates) produced in Russia from fish raw materials using bioconversion, such as Biomarin, Bioprom and Vakhob. General chemical composition of tested products was determined by standard methods of analytical chemistry; composition and content of fatty acids — by gas-liquid chromatography; microand macroelements, as well as toxic metals — by atomic absorption spectrophotometry; fractional composition of proteins and peptides — by high pressure gel permeation chromatography; amino acid composition — by ion exchange chromatography on a high-speed analyzer. All tested samples contain similar amount of the main feed component — protein substances. The quantitative ratio of peptide fractions is also comparable, the sum of the most active fractions (MW 0.1−10.0 kDa) in TINRO-60 and Biomarin is close to their level in tissues of Artemia, natural food for fish fry. The content of essential amino acids, EPA and DHA is significant in Biomarin, TINRO-60 and Bioprom, but almost twice lower in Vakhob. Analysis of mineral composition showed that bioconversion into dry fermentolysates does not cause concentration of toxic elements. High quality of the protein feed additive TINRO-60 produced by bioconversion of nonstandard fish raw materials under certain conditions is proved.

Gim (Porphyra yezoensis) Flakes for Decreased Sodium Content of Fried Surimi Fish Cake

ABSTRACT The study was to investigate the influence of the addition of sea vegetable (gim) flakes on physicochemical, nutritional, and antioxidative properties and stability over storage of salt-reduced fried fish cake. The addition of gim flakes at 1%, 2%, and 3% (w/w) in fried fish cake reduced the salt content by 13%, 15%, and 18%, respectively. Fried fish cakes prepared with gim flakes demonstrated lower fat and sodium content and higher protein, phenolic content, and antioxidative properties. The results of these studies demonstrated that the beneficial value and overall quality of fried fish cake can be improved through the addition of gim.

Influence of microplastic pollution on the toxicity of potamodromous fish grass carp (Ctenopharyngodon idellus) and its swimming capacity

Microplastics (MPs), as a ubiquitous environmental contaminant in marine and freshwater systems, produced a significant influence on the physiological characteristics of aquatic organisms, and inevitably posed unknown effects on their swimming capacity. Herein, we evaluated the MPs accumulation in potamodromous fish, Ctenopharyngodon idellus, and their potential effects on oxidative stress, neurotoxicity, gut microbial diversity, and swimming capability through a toxic-control experiment. Juvenile fish were exposed to 5 µm polystyrene-MPs (PS-MPs) for 6 days at concentrations of 0.1, 1, and 10 mg/L. Exposure to PS-MPs resulted in significant inhibition of acetylcholinesterase (AChE) in the brain of fish, with significant increases in superoxide dismutase (SOD) activity and malondialdehyde (MDA) levels at 1 and 10 mg/L exposures. Meanwhile, MPs altered grass carp gut microbiota and reduced the Shannon diversity index. In addition, MPs significantly increased induced swimming speed by observing the flow rate at which grass carp happened to produce a reverse current behavioral response. The 1 and 10 mg/L of MPs treatments can significantly reduce the critical swimming speed of grass carp, meaning that the completion of the life history of grass carp may be delayed. Furthermore, there were significant correlations between biomarkers and indicators of swimming capacity. Therefore, the present study suggests that MPs produced a negative effect on the physiological properties of fish, reducing the swimming capacity of migratory fish.

Turbidity effects on prey consumption and survival of larval European smelt (Osmerus eperlanus)

The anadromous European smelt (Osmerus eperlanus) plays a key role in food webs of many riverine ecosystems in Europe. However, population sizes in several German rivers (e.g. Elbe or Weser rivers) have diminished drastically over the past decade. Turbidity has been considered one of the stressors affecting the successful recruitment of European smelt, as their early life stages may be particularly sensitive to changes in the abiotic environment. In this study, we investigated whether prey consumption and survival of European smelt larvae would be negatively affected by an acute exposure to elevated turbidity. We reared the larvae in the laboratory and exposed them in four separate trials (18 to 26 days post hatch, 9.5 ± 0.8 mm standard length, mean ± SD) to six turbidity levels (0–500 NTU, nephelometric turbidity units). We found that prey uptake increased at low turbidity levels and decreased at high turbidity levels, with an optimum between 100 and 200 NTU. Survival started to decrease at turbidity levels above 300 NTU. In addition, we conducted a systematic literature analysis in which we found that prey consumption of larval and juvenile fishes had been tested across a wide range of turbidity levels, mostly using pelagic (e.g. planktonic) prey items, with more studies focusing on perciform fishes and juvenile rather than larval life stages. Our empirical findings contribute to establishing thresholds for optimal larval European smelt performance under increased turbidity and provide valuable information for developing mechanistic models that assess potential consequences for European smelt recruitment dynamics.

Population status and host fishes of the freshwater pearl mussel in the eastern part of the Onega Peninsula, Northern European Russia

Four populations of freshwater pearl mussel Margaritifera margaritifera were studied at lower sections of three river basins of the eastern part of the Onega Peninsula, Northern European Russia: the Bol’shaya Syarta, the Ust’-Yaren’ga and the Lopshen’ga (including Kamenny Stream). One of the populations from the Lopshen’ga River was discovered for the first time. Here we present preliminary data on the population status of M. margaritifera, its host fishes and glochidia infestation in the studied river basins. Living juvenile mussels and fishes infested by glochidia were recorded only in two waterbodies, i.e., the Bol’shaya Syarta and Ust’-Yaren’ga rivers. The pearl mussel population from the Bol’shaya Syarta River seems to represent the most prosperous among studied ones. The average density of visible mussels was small in the lower section of the river, but the proportion of young mussels was rather high (33.1 %) and intensity of glochidia infection reached 865 glochidia per fish. The highest average density was recorded in the pearl mussel population from the Kamenny Stream, Lopshen’ga River basin. However, only one juvenile mussel and none of host fishes infested by glochidia were recorded in this watercourse that may indicate the population aging and decrease of reproduction. Morphological analyses revealed significant differences between four studied populations of M. margaritifera towards the shell convexity index (SCI) and shell elongation index (SEI). In all studied basins, salmonid fishes were also infested by other parasites, mainly flatworms and their cysts. This factor may negatively impact the salmonid host fish populations that require monitoring of the current situation. The data obtained and future studies will allow to develop a system for protecting and monitoring of populations of a rare species such as the freshwater pearl mussel M. margaritifera.

Nutrient Composition of Nine Festival Dishes Obtained from A Recipe Survey Among Lower to Middle-Income Households in Selected Urban Areas

Background and Objectives: Estimation of nutrient content of a recipe by a recipe calculation method may be cost‐effective and alternative to the chemical analysis for a range of applications, laboratory analysis of standardized recipes is considered a more authentic and accurate source of recipe nutrient data. Food composition data (FCD) regarding festival foods and dishes is very scanty in local and global food composition tables (FCT). The present study, thus, conducted a recipe survey on the ingredient profile of festival recipes consumed by lower to middle-income households in Bangladesh followed by proximate analysis of standard recipes obtained by collapsing similar recipes. Unanalyzed nutrients were obtained by data compilation from local and global food composition databanks (FCDB). Methodology: A cross-sectional recipe survey was conducted sequentially on festival foods and dishes among purposefully selected housewives residing at different areas of Dinajpur district and Dhaka city. The study instrument was a structured pre-tested questionnaire. Nine homemade festival recipes out of 40 recipes cited viz., plain polao, beef bhuna, fish fry, chicken bhuna, payesh, beef biriyani, chinese vegetable, chicken roast and baked fish were selected and standardized according to the method established in our laboratory. The selected recipes were prepared and analyzed for proximate composition along with an estimation of the cooking yield factor. Content of moisture, ash, protein, total fat, total dietary fiber (TDF), available carbohydrates, and calorie values of nine selected dishes were determined using standard operating procedures (SOP) established on the basis of AOAC methods. Precision and accuracy of analytical values were checked as part of Quality Assurance Program (QAP). Data compilation of missing values for vitamins and minerals was conducted according to FAO data compilation toolkit. Result: Moisture content ranges from 30.42-70.75%, protein content ranges from 2.60-35.70%, fat content ranges from 2.61-22.53%, ash content ranges from 0.6241-8.8%, TDF ranges from 0.58-8.49%, carbohydrates ranges from 0.65-45.7% and energy content ranges 101.5-368.4 kcal/100g fresh sample. The cooking yield ranges from 40.96-96.82%, which is highest in plain polao and lowest in fish fry. Conclusion: The data generated from this study can be used as reliable data which will enrich the national food composition table. Bioresearch Commu. 10(2): 1516-1523, 2024 (July)

REALISM AND COMPOSITIONAL REPRESENTATION OF REALITY : AN ANALYSIS OF THE MANIPURI DOCUMENTARY FILM “FRIED FISH CHICKEN SOUP AND A PREMIERE SHOW”

The debate around realism in documentary cinema has evolved significantly over the years reflecting broader shift in filmmaking techniques, compositional forms, audience expectation, cultural and political contexts. The realms of realism and compositional documentary have been in a constant state of flux, each genre pushing the boundaries of what is considered truth, authenticity, and artistic expression thereby blurring the lines between reality and fiction, and challenging the traditional notions of documentary filmmaking. Several Manipuri documentary films have made endeavors of recreating the reality through their representation on cinematic canvas. Depicting Manipur’s cinematic journey and its socio-political context in a compositional form, the documentary film “Fried Fish, Chicken Soup, and a Premier Show” (2012) relies heavily on editing with found footage and presents an even greater challenge with the inclusion of historical narratives. It intricately combines observational account of a film crew at work during the filming of the Manaobi MM’s Manipuri feature film “21st Century Gee Kunti” (2010) with intertitles, archival footage etc. to depict the history of Manipur. This paper explores the realism and compositional representation of reality in the film which skillfully blends diverse elements to document the trend of change and transformation within the cinematic landscape and the lived reality of Manipuri society in transition.

AFLATOXIN CONTAMINATION AND NUTRITIONAL EVALUATION OF DRIED JUVENILE FISH (Clarias gariepinus) SOLD IN IBADAN METROPOLITAN MARKETS

The contamination of food due to the occurrence of mycotoxigenic fungi is a public health concern. Therefore, fungi and aflatoxin contamination of smoked-dried juvenile fish (SDJF) (Clarias gariepinus) were investigated. The samples were purchased from three major markets in Ibadan. The total fungal count ranged from 1.0 x 103 to 12.0 x 103 CFU/g. Thirty-two fungi were isolated, including Penicillium sp., Rhizopus sp., Alternaria sp., Aspergillus flavus, Aspergillus niger, and Aspergillus ochraceus. A. niger had the highest frequency of occurrence (38%), while A. ochraceus (3%) had the lowest. All the samples were contaminated with aflatoxin. The total aflatoxin content ranged from 0.237 to 1.995 ppb. Of the 11 Aspergillus strains obtained from the samples, 5 were aflatoxigenic, while 6 were not. 85 and 94% of the mycobiota were xerophilic and halophilic. The percentage moisture content, crude protein, crude fat, and ash content in the samples ranged from 12.99–17.82%, 68.72–77.62%, 0.49–6.00%, and 6.97–12.24%. Phosphorus and potassium concentrations of the SDJF samples ranged from 388.2–509.6 mg/100g and 1113.8–1517.0 mg/100g, while lead and cadmium were not detected in the samples. Though the level of aflatoxin contamination in this study was within the maximum limit permitted (20 ppb), proper attention is needed for adequate preservation before sales and consumption.

A Case Study on Economic Analysis of Sea Cage Farms in the Black Sea, Türkiye

The main aim of this research is to understand the value chains of enterprises engaged in aquaculture in sea cages in the Black Sea region of Türkiye, to determine production costs and to make a general analysis of the aquaculture sector. Random sampling method was used to ensure that farmers were equally represented in the survey. Data for the survey were randomly selected from 16 separate farms spread throughout 4 different marine cage locations. Furthermore, fish traders and sector stakeholders were interviewed. The businesses examined within the scope of the study are divided into 3 groups: small (250 -500 tons/year), medium (501-999 tons/year) and large (>1000 tons/year), according to their capacities. The most important expense items of enterprises consist of variable costs. Among the variable costs, the purchase of fry fish, feed purchase, and labor costs constitute the most important expenditure items. Among the fixed costs, the most important expense is depreciation costs. The unit cost of one kg of fish varies between 2.7 and 3.0 euros. Considering that the trout (Oncorhynchus mykiss) and seabass (Dicentrarchus labrax) in the Black Sea are at the level of 3.5 Euro, the profit rate of the enterprises is between these levels. Recently, since trout from the Black Sea has been exported to the Far East Country (particularly Japan), its price has also increased. In 2018, the average retail price (including VAT) and medium selling price of seabass and trout were at a level of 5.24 and 5.34 Euros respectively. Despite all these positive developments, climate change continues to pose a threat in terms of disease outbreak and marketing problems.

Mangrove ecosystems as fundamental habitats for fish from the Mexican Caribbean: An evaluation between a conserved and restoration zone

Mangrove ecosystems can function as a habitat for many juvenile marine fish species, with provisions of food and refuge. Seemingly, these ecosystems have been extensively reduced due to anthropogenic activity, as is widespread land use and road construction along the coastline. Nonetheless, much needed restoration efforts have increased tremendously over time. This study analyzes fish community, and the manner in which habitats in the mangrove ecosystem are used, comparing two mangrove zones, a conserved zone (healthier state) and one undergoing restoration. Hydrologically, no significant differences were registered (KW p>0.05). Of the 24 species registered, marine species were dominant in the conserved zone and estuarine species dominant in the restoration zone. Juvenile fishes were more abundant in the conserved mangrove zone, with a higher proportion of adults found in the restoration zone. According to Hutcheson’s t test, fish diversity showed significant statistical differences between sites combined with distinct climatic seasons. The Canonical Correspondence Analysis (CCA) indicated a relationship between secondary freshwater species Floridichthys polyommus and Cyprinodon artifrons and greater salinity and temperature, whereas marine species had a higher relationship with well oxygenated sites. A high number of marine fish species in juvenile stage in the conserved area may relate to mangroves functioning as nurseries. This can serve as a useful indicator by managers taking an integral approach to evaluate and monitor present and future mangrove restoration programs and pathways.

Community structure of whole pelagic copepods along the Kuroshio: Increase in the abundance and size in the north frontal area of the Kuroshio axis near the Japanese archipelago

The Kuroshio ecosystem is an important nursery ground for various fish species. Because the prey biomass and composition influence the recruitment of larval and juvenile fish, we investigated the variation in the abundance, carbon biomass, and community structure of copepods, which are the main prey for larval and juvenile fish, along the Kuroshio from the eastern coast of Taiwan to the Boso Peninsula, Japan from 8–November 24, 2015, using 100 μm-meshed plankton net samples. We identified two groups of stations (A and B) by the cluster analysis based on the composition and abundance for adult copepods (Q-mode). The total copepod abundance and carbon biomass were higher in Group A than in Group B. Of the dominant species assemblages classified by cluster analysis (R-mode), the abundance of species assemblages S2b and S3, which were composed of small-sized species (e.g., Oithona and Oncaea species), did not differ between Groups A and B, indicating that they were distributed abundantly throughout the Kuroshio region. On the other hand, the species assemblages (S1 and S2a) including the medium-sized calanoid copepods of coastal species and subtropical species (e.g., Paracalanus aculeatus and Clausocalanus furcatus) contributed to the high abundance and biomass of Group A. Group A occurred in the north-frontal area of the Kuroshio axis near the Japanese archipelago where chlorophyll a was high. This indicates that the community was changed by the bottom-up processes driven by nutrient supply from the subsurface layer in the north-frontal area. These results show that although the small-sized copepods were usually dominant in numerical abundance in the Kuroshio region as well as other oligotrophic oceans, the medium-sized copepods were an important component in the copepod community in water with high primary production. We concluded that the ecosystem in the north-frontal area downstream of the Kuroshio might provide optimal prey environments for diverse fish larvae and juveniles.

Transcriptome-Based Analysis of the Mechanism of Action of Metabolic Disorders Induced by Waterborne Copper Stress in Coilia nasus.

To reveal the effects of waterborne copper stress on gene expression changes, molecular pathways, and physiological functions in Coilia nasus, juvenile fish were equally divided into two experimental groups, and the copper levels were 1.61 ± 0.03 mg/L (copper-exposed group) and 0 mg/L (control group), respectively. After 4 h, gill tissue samples were collected for transcript sequencing analysis, and two libraries were constructed from the copper treatment group (Cu) and the control group (C) and sequenced using Illumina sequencing technology. The results showed that approximately 40.2-46.0 M clean reads were obtained from each library, and the percentage of uniquely mapped transcripts ranged from 80.57 to 84.93%. A total of 3915 differentially expressed genes (DEGs) were identified under waterborne copper stress, among which 1300 genes were up-regulated, and 2615 genes were down-regulated. Twelve DEGs were randomly selected for quantitative RT-PCR (qRT-PCR) analysis, and the results confirmed that the transcriptome analysis was reliable. Furthermore, the DEGs were subjected to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, and the results showed that most of the DEGs were involved in metabolic pathways, including steroid biosynthesis, glutathione metabolism, and peroxisome proliferator-activated receptor (PPAR) signaling pathways. Furthermore, due to the waterborne copper levels, gsk-3β was significantly up-regulated, while other metabolism-related genes (tor, pi3k, lpl, aqp7, fabp3) were significantly down-regulated. In addition, the copper-exposed group significantly reduced the expression of some immunity genes (ifn-γ, stat1, cxcl10, and tgf-β), and enhanced the expression of il-1β and tnf-α. In summary, these results indicated that copper causes metabolic disorders and insufficient energy supply in the body, and induces oxidative stress, which results in reduced immune functions.

When to Go Against the Flow: Examining Patterns of Performance Over Multiday Migration Events in the Hawaiian Stream Fish, 'O'opu Nōpili (Sicyopterus stimpsoni).

Many animals migrate across regions of their geographic range as part of extended events, with groups of individuals proceeding through areas of travel on several successive days. Early migrating individuals may have an advantage over late migrating individuals by gaining early access to the resources at the eventual destination. For situations where early access to resources would provide an advantage, specific sets of locomotor traits might be found among individuals that are earlier migrators. We tested for associations between migration timing and traits related to escape responses, climbing, and morphology in the amphidromous Hawaiian stream goby, 'o'opu nōpili (Sicyopterus stimpsoni). In this species, juvenile fish migrate in pulses over several days immediately following flash floods. We collected daily measurements of escape responses and waterfall climbing from juvenile fish arriving at streams from the ocean. We found that escape performance showed mainly stochastic variation across migrating individuals tested on successive days. In contrast, some metrics of climbing performance decrease over successive pulses during a migration event. We also found more variation in body shape among fish from early pulses during migration events compared to later in pulses. These results could have implications for guiding conservation efforts, identifying critical time windows for protection as periods with the greatest likelihood of successful migrants.

Physiological sensitivities to hypoxia differ between co-occurring juvenile flatfishes

Coastal hypoxia threatens estuarine nursery habitat for juvenile demersal fishes worldwide, and is expected to intensify with climate change. This study examines the physiological tolerances of hypoxia in two ecologically and economically important flatfish species that co-occur in a highly eutrophic estuary and biodiversity hotspot on California's central coast, the Elkhorn Slough. Juveniles of English sole (Parophrys vetulus) occur less frequently in areas of the slough where dissolved oxygen (DO) ≤ 4.0 mg/L O2 compared to speckled sanddabs (Citharichthys stigmaeus), suggesting that English sole may be more sensitive to hypoxia. We exposed both species to an ecologically relevant, acute six-hour exposure to six DO levels ranging from ambient to severely hypoxic: 8.0, 6.0, 4.0, 3.0, 2.0, and 1.5 mg/L O2 and measured known physiological and biochemical indicators of hypoxia stress. As DO declined, metabolic rate and aerobic scope decreased for English sole, while anaerobic activity (measured by L-lactate) and ventilation rate increased for both species. Biochemical responses to hypoxia were observed only at very low DO levels (≤ 4.0 mg/L O2), indicating that both species appear to have a higher tolerance for relatively short-term hypoxia than other teleost fishes. Speckled sanddabs increased ventilation rate and anaerobic activity at higher DO levels than English sole, suggesting that earlier onset of compensatory mechanisms may contribute to the greater relative hypoxia tolerance in sanddabs. Examining the link between physiological and ecological thresholds for hypoxia tolerance will help determine suitable nursery habitat areas and management targets for estuarine restoration, and aid in predictions of fishery success under eutrophication and climate change.

Integrating Iso-seq and RNA-seq data for the reannotation of the greater amberjack genome

The greater amberjack is a very important fishery species with high commercial value, and it is distributed worldwide. Transcriptome-based studies on S. dumerili have been limited by an inadequate reference genome and a lack of well-annotated full-length transcripts. In this study, a total of 12 tissues from juvenile and adult fish both sexes were collected for next-generation RNA sequencing (RNA-seq) and full-length isoform sequencing (Iso-seq). For Iso-seq, a total of 163,218, 149,716, and 189,169 high-quality unique transcript sequences were obtained, with an N50 of 5,441, 5,255, and 5,939, from juvenile, adult male and adult female S. dumerili, respectively. We integrated the Iso-seq and RNA-seq data to construct a comprehensive gene annotation and systematically profiled the dynamics of gene expression across the 12 tissues. Our gene models had greater detail and accuracy than those from NCBI and Ensembl, with more precise polyA locations. These resources serve as a foundation for functional genomic studies and provide valuable insights into the molecular mechanisms underlying the development, reproduction and commercial traits of amberjack.

Seasonal dynamics and habitat preferences of juvenile fish assemblages in the Wanquan Estuary, South China: Implications for conservation and management

Tropical estuaries encompass diverse habitats, which are crucial for supporting juvenile fish by providing nurseries, refuges, and migration routes. In the present study, we investigated the seasonal and spatial dynamics of juvenile fish assemblages in the Wanquan Estuary, Hainan Island, China, examining variations during the wet and dry seasons across four types of habitats. Our research aimed to test the hypotheses: (1) the wet season supports a greater abundance and species richness of juvenile fish compared to the dry season, and (2) juvenile fish showed varying habitat preferences across seasons. We recorded a total of 3617 individuals belonging to 33 families, 50 genera, and 78 taxa. Our findings revealed significant seasonal fluctuations in the assemblage structure, with peak abundance during the wet season in August, primarily consisting of diadromous species. A notable shift towards marine species was observed in March. Spatially, juvenile fish exhibited significant habitat preferences, with a strong preference for sand substrates for most species. Contrary to common expectations, mangrove fringe habitats were not identified as the primary nursery grounds for juvenile fish. Instead, our study highlights the importance of habitat diversity and connectivity in enhancing nursery functions. Water temperature and salinity were the key drivers influencing the seasonal and temporal patterns of juvenile fish assemblages in the Wanquan River estuary The pronounced temporal dynamics of these assemblages, driven by seasonal environmental alterations affecting water variations and habitat connectivity, were more significant than spatial differences. The findings emphasize the need for focused connectivity of various habitats to support the conservation of diverse fish communities in tropical estuarine ecosystems.

Capture–translocation restores spawning migration connectivity of Razorback Suckers in the fragmented San Juan River

AbstractObjectiveBarriers to movement negatively affect population vital rates of riverine fishes that rely on connected migratory routes to complete components of their life cycle, such as reproduction and recruitment. In the southwestern United States, decades of water diversion, construction of large impoundments, and loss of floodplain habitats have all contributed to highly fragmented riverscapes. A capture–translocation strategy was implemented for Razorback Suckers Xyrauchen texanus in the San Juan River to mitigate the negative effects of two barriers while precluding the upstream movement of nonnative species. We hypothesized that translocated individuals would remain upstream of barriers during the spawning season and that aggregations of translocated Razorback Suckers would be identified upstream in spawning habitats.MethodsWe used radiotelemetry to assess movement of Razorback Suckers after translocation above the two barriers. We deployed fixed remote radio receivers to determine residency time above each barrier and conducted mobile telemetry surveys to monitor upstream destinations after translocation.ResultAlthough most Razorback Suckers returned downstream of barriers within 2 months of translocation, we provide evidence that most individuals remained upstream long enough to successfully spawn. After translocation above the Piute Farms Waterfall, 80% of individuals remained upstream for 26 days in 2020 and for 23 days in 2021. Further upstream (307 km), at a weir operated by the Public Service Company of New Mexico, 80% of translocated individuals remained above the barrier for 37 days in 2021 and for 25 days in 2022. After fish translocation above both barriers, we observed upstream movements ranging from 2 to 262 km and we detected distinct aggregations within the expected spawning season.ConclusionAlthough translocation efforts seasonally reconnect migratory routes for a proportion of the population and may increase spawning potential, other conservation actions are likely still needed to improve recruitment conditions for juvenile fish.

Shallow estuarine reef as nursery habitat for Australasian snapper (Chrysophrys auratus)

ABSTRACT Estuaries are important recruitment sites for many fish species, with structurally-complex habitats such as subtidal seagrass beds on soft sediments particularly valuable due to their provision of food and shelter. Soft sediments dominate most estuaries, but where hard-bottom reefs are present they have the potential to act as nursery habitats for juvenile fish. We document recruitment of juvenile Australasian snapper (Chrysophrys auratus) to a shallow linear sandstone reef in Whangateau Harbour, a small estuary in north-eastern New Zealand. Up to several hundred 0 + juveniles (∼20–70 mm fork length) were present on the reef during early summer to mid-late autumn each year from 2018 to 2021. Numbers were consistently highest at the seaward end of the reef, facing into incoming tidal currents, and lowest in the deeper central part of the reef, where larger, potentially cannibalistic, snapper were common. Juveniles disappeared from the reef fairly abruptly at the end of each season, with departure in at least two of the years appearing to follow a sudden decrease in water temperature rather than being associated with body size or absolute temperature. Although relatively small in area, estuarine reefs may be increasingly important nursery habitats in the future given the widespread loss of subtidal seagrass beds.

Unravelling spermatogenesis in spotted wolffish: Insights from the ultrastructure of juvenile male testes to the cryopreservation of broodstock sperm

The aim of this study was to deepen our understanding of the reproductive biology of male spotted wolffish (Anarhichas minor) using two different experimental approaches involving juvenile and mature broodstock fish. The first approach consisted of a detailed histological examination of the testes to identify the onset of gonadal maturation and characterise the spermatogenic stages in two- and three-year-old juvenile specimens. Light microscopy analysis revealed clear differences between the age groups. Two-year-old fish displayed well-defined interstitial tissue, Sertoli cells and cysts housing spermatogonia stem cells in which meiosis had not yet begun. In contrast, three-year-old fish exhibited cysts containing spermatocytes, spermatids and abundant spermatozoa, indicating the initiation of the spermatogenic cycle, albeit with asynchronous puberty. Histochemical staining revealed a significant presence of smooth myoid cells in the interstitial tissue of sexually mature fish, while electron microscopy further revealed synaptonemal complexes indicating the onset of meiosis and centriolar structures that gave rise to flagella. The second approach focused on optimising semen freezing and cryopreservation procedures in mature broodstock individuals over the age of 10 years. Seven freezing extenders (KT, TS-2, OP, MT, MH, HBSS, or SR), with seawater (SW) as a control, were assessed along with two cryoprotectants dimethylsulfoxide (DMSO) or methanol to evaluate their impact on pre- and post-thaw semen quality. Results showed that the MT and HBSS extenders were superior in total sperm kinetics at 1:3 dilution, and that DMSO showed optimal results in sperm motility and velocity variants. Moreover, the MT and HBSS groups demonstrated consistent sperm viability after cryopreservation, with values similar to fresh samples. Based on the viability results of the SYBR-green-14/PI assay comparing fresh and cryopreserved sperm using MT and HBSS, the MT extender emerged as the most effective freezing medium for cryopreservation of spotted wolffish broodstock sperm. In conclusion, this study provides a comprehensive understanding of the reproductive dynamics of male spotted wolffish, offering valuable insights for both scientific research and aquaculture management.