Juvenile Fish Research Articles

Assessment of Food Safety Practices, Associated Factors and Microbial Contamination of Fried Nile Perch in Mwanza City Markets: A Cross-Sectional Study

Unsatisfactory hygienic practices can lead to food-borne pathogen contamination in fish and fishery products, posing serious health concerns for consumers. This study assessed the food safety practices, their associated factors, and microbial contamination levels of fried Nile Perch in Mwanza City across three markets: Kirumba, Butimba, and Nyakato. A cross-sectional study using a structured questionnaire examined the food safety practices of traders and processors, and their associated factors, including experience, income, and training. Standard methods for microbial analysis were conducted to determine the levels of coliforms, Escherichia coli, and Staphylococcus aureus. SPSS version 27 was used to compute the frequency and percentages. The factors and behaviours of fried Nile perch processors and traders were assessed using a 95% chi-square test. R software was employed to perform the Aligned Rank Transformation on market microbiological mean contamination. Tukey's Honest Significant Difference was employed for post hoc group comparisons. The results show that the transportation of raw fish at ambient temperature conditions showed a significant association across markets (X²=6.153, p=0.046), risking high levels of microbial contamination. Furthermore, tap water served as the predominant water source in the Butimba (88.9%), Kirumba (90%), and Nyakato (100%) marketplaces, despite the insufficient hand-washing facilities in the markets. Low income significantly affected the clear separation between storage and processing areas (X²=16.201, p=0.013), while insufficient training was related to inadequate temperature control (X²=6.032,p=0.014). Fried fish from all markets exceeded the safe limits of assessed microorganisms, with Nyakato having the highest levels of total plate count (9.53 log CFU/g), coliforms (8.74 log CFU/g), and S. aureus (5.51 log CFU/g), posing significant risks of food-borne illnesses upon consumption. Contamination levels differed significantly between markets (p<0.05), despite similar activities across locations. Consumers should reheat fried Nile perch before consumption to avoid foodborne illnesses, and the government should offer formal training in food safety and environmental cleanliness to food safety operators to facilitate compliance with safety regulations.

The function of the Wadden Sea in the life cycle of small pelagic fish

Most fish species require different habitats to complete their life cycle, with coastal areas often playing a crucial role as nursery areas for juveniles. The Wadden Sea is an important nursery area for juvenile fish in the North Sea ecoregion. Despite extensive research on the nursery function of the Wadden Sea for demersal species, its role in the life cycle of small pelagic fish (SPF) remains largely unknown. This limits our understanding of the Wadden Sea ecosystem, as SPF are the dominant component of the overall fish biomass and serve as important food source for higher trophic levels. We studied the role of the Wadden Sea in the life cycle of Atlantic herring (Clupea harengus), European sprat (Sprattus sprattus), European smelt (Osmerus eperlanus) and European anchovy (Engraulis encrasicolus) through monthly stow net and seasonal trawl surveys. Our study showed that SPF use the Dutch Wadden Sea primarily as juvenile habitat, with herring being the dominant marine juvenile representative. Length frequency distributions and genetic analysis revealed that the juvenile herring originated predominantly from southwestern waters, such as the English Channel. Additionally, the Wadden Sea still provides spawning grounds for herring and anchovy, with no substantial spawning observed for sprat. While smelt can complete nearly its entire life cycle in the Wadden Sea, it depends on connectivity to nearby freshwater for spawning. In summary, the Wadden Sea functions as a nursery for juveniles, and to a lesser extent as spawning grounds for adults. A thorough understanding of these functions is crucial for identifying bottlenecks and implementing effective conservation and management strategies.

The enzymatic and transcriptional adverse effects of hull in-water cleaning discharge on juvenile rockfish (Sebastes schlegeli)

The hull in-water cleaning (IWC) process creates chemical contaminants, including antifouling paint particle mixtures that are directly discharged into the coastal environment. Recent attention has also been paid to the international regulation of ship hull cleaning discharges in environmental media. However, few studies have investigated the adverse effects or toxic pathways on resident marine species. In this study, we evaluated the chemical concentration of IWC discharge in situ and its toxic effects on juvenile rockfish (Sebastes schlegeli), a major coastal fishery resource, using enzymatic and transcriptomic studies. Zinc (8.05 ± 0.96 to 189.96 ± 47.76 μg/L) was the most abundant substance in IWC discharge, followed by copper (0.87 ± 0.19 to 1.97 ± 0.60 μg/L). No mortality was observed after 7 days of exposure in any experimental group; however, reactive oxygen species and acetylcholinesterase activity varied in juvenile rockfish exposed to the highest concentration of IWC discharge (10-fold-diluted IWC discharge). The immune and detoxification systems in juvenile rockfish exposed to IWC discharge were also significantly affected in juvenile rockfish exposed to 10-fold-diluted IWC discharge (zinc: 189.96 ± 47.76 μg/L, copper: 1.97 ± 0.60 μg/L). The expression of genes related to oxidative stress, including Cu/Zn-SOD, GST, and CAT, increased significantly in fish in all the exposure groups. Specifically, brain transcriptomic analysis revealed disturbances in the nervous system and homeostatic processes. Although lethal toxicity was not significantly affected, these findings indicate the potential hazard posed by sub-lethal concentrations of IWC discharge to juvenile fish, which are at a high-level in the food chain. Our enzymatic and transcriptomic results showed that Zn-dominant IWC discharge exposure may cause neuronal and immune toxicity in marine fish species, providing relevant insights into the management of hull IWC discharge to protect coastal ecosystems against chemical contaminants.

Analysis of the cardiotoxic and myorelaxant effects of camphor on fish of the Nile tilapia species (Oreochromis niloticus) (Linnaeus 1758)

The present study aimed to characterize the behavior and evaluate the electromyographic (EMG), electrocardiographic (ECG), and respiratory responses of Nile tilapia (Oreochromis niloticus) when exposed to different concentrations of Camphor (CPR) as a potential anaesthetic in immersion and recovery baths. The goal was to determine the impact of CPR on muscle, cardiac, and respiratory functions, and assess its suitability as an anesthetic for tilapia. Therefore, juvenile fish (38.2 ± 5.5 g) were acclimatized in aquaria for 20 days under controlled environmental and water quality conditions. Four concentrations of CPR (150, 200, 250 and 300 mg L−1) were used in immersion baths to evaluate behavioral, EMG, ECG changes and recordings of opercular beats during the short-term treatment (5 min of exposure). The latency time for loss of the postural reflex was dependent on the CPR concentration. The EMG recordings demonstrated muscle activity during treatment and recovery. The ECG and opercular beat recordings demonstrated a decrease in heart and respiratory rates, with changes in the recorded tracings being more evident at higher concentrations. However, the use of a concentration of 300 mg L−1 makes the cardiac and respiratory effects more evident, with changes in the tracing, which can harm the animal’s hemodynamics. However, lower concentrations (150 mg L−1) showed tachycardia and opercular hypermotility, demonstrating changes not compatible with anesthesia. This article demonstrated that CPR in high concentrations can be harmful to the hemodynamics of tilapia, causing electrocardiographic and respiratory changes for a long period, even after recovery of muscular activity and postural reflex.

Assessment of the nutritional and effluent properties of potential fish-meal-free diets for rainbow trout (Oncorhynchus mykiss W.) in Iran

Research is needed on alternative ingredients for aquafeeds due to rising demand and limited fish meal availability. This study evaluated fish-meal–free diets for rainbow trout in two phases. The first phase focused on assessing the growth performance and nutrient digestibility of six cold-pelleted diets. Aside from the control diet, the test diets contained poultry protein concentrate, blood meal, low-ash poultry by-product meal, 20–40% canola meal, and feather meal (Goldmehl®). Juvenile fish, averaging 5.3 g, were fed the diets for 56 days in a random-block design with four replicates per feed. Feces were collected using the settling method to evaluate nutritional digestibility and phosphorus availability. The feed from the primary phase, which resulted in the least-cost feed conversion ratio, was extruded and fed to fingerlings (14.6 g) in the second phase. This trial added to the first run in measuring digestibility parameters over a 28-day period. In parallel, extruded feed was given to grow-out fish, averaging 172.5 g, for 55 days in triplicate completely randomized tanks to evaluate growth performance and nutrient effluents. Throughout all the experimental runs, a casein-based laboratory pelleted feed was used for the respective controls. Feeding rainbow trout with 35% canola meal in both pelleted and extruded forms showed comparable results (P > 0.05) to the control in terms of growth performance and apparent digestibility for lipid (> 91%), crude protein (> 87%), and organic matter (> 78%). The extruded feed in this study represents an eco-friendly option for the growing aquafeed sector.

Ontogenetic shifts by juvenile fishes highlight the need for habitat heterogeneity and connectivity in river restoration

AbstractLarge‐scale anthropogenic river modifications have caused the loss of critical floodplain nursery habitats for riverine fish, leading to population declines. Restoration efforts have been implemented to recover these habitats, but with varying success. Understanding how larval and juvenile fish use habitats in dynamic river environments is essential for improving restoration strategies. We assessed ontogenetic shifts in habitat use by young‐of‐the‐year fishes in the lower Rhine, analyzing 2167 samples across 18 restored floodplains over three growing seasons (2018–2020). Five distinct nursery habitats were identified: (1) exposed, fast‐flowing habitats with coarse substrate; (2) turbid, nonflowing areas with high turbidity and chlorophyll; (3) shallow, vegetated habitats with macrophytes and shoreline vegetation; (4) deeper, sheltered habitats with structural complexity; and (5) shallow, slow‐flowing areas. Habitat use shifted significantly with ontogeny across species. Larvae generally preferred shallow habitats (< 50‐cm depth), either in slow‐flowing areas (e.g., asp, ide, monkey goby, nase, and whitefin gudgeon) or vegetated zones with macrophytes (e.g., bleak, bitterling, bream, round goby, and zander). Juveniles increasingly used deeper habitats (> 50‐cm depth), favoring fast‐flowing areas (e.g., asp, barbel, ide), or deeper, nonflowing habitats (e.g., bream, zander). Our findings thus highlight the critical importance of habitat heterogeneity and connectivity for riverine fish biodiversity. Restoration strategies should prioritize the creation of a mosaic of shallow, low‐velocity habitats for larvae, alongside deeper, fast‐flowing, or sheltered areas for juveniles. Additionally, the movement of rheophilic species from floodplain habitats to the main river channel emphasizes the need for maintaining continuous connectivity between floodplains and the river.

Exposure to lower temperature during early development decreases hypoxia tolerance in juvenile Fundulus heteroclitus.

Cross-protection occurs when exposure to one stressor confers heightened tolerance against a different stressor. Alternatively, exposure to one stressor could result in reduced tolerance against other stressors. Although cross-protection has been documented in a wide range of taxa at juvenile and adult life stages, whether early developmental exposure to a stressor confers cross-protection or reduced tolerance to other stressors later in life through developmental plasticity remains largely unexplored. In this study, we examined whether altered temperature during embryonic development results in developmental plasticity in upper thermal tolerance or hypoxia tolerance using a small topminnow, Fundulus heteroclitus, and examined potential underlying molecular mechanisms. We incubated embryos at one of two ecologically relevant temperatures (20 °C or 26 °C) until hatch. Once hatched, fish were raised at a common temperature of 20 °C for one year, and tolerance was assessed in both juveniles (6 months) and early adults (1 year). Developmental temperature had no significant effect on thermal tolerance (CTmax) in juvenile fish, or on the transcript abundance of thermal-tolerance related genes (constitutive heat shock proteins, hsc70, hsp90b). In contrast, reduced developmental temperature decreased hypoxia tolerance but increased transcript levels of the hypoxia inducible factor hif1α in juvenile fish but the effects were less evident in older fish. Overall, we found no indication of developmental plasticity for thermal tolerance, but there was evidence of negative impacts of lower developmental temperature on hypoxia tolerance in juveniles associated with changes in gene expression, providing evidence of developmental plasticity across stressors and levels of organization.

Assessment of the physiological state of the Caspian beluga juveniles before release into their natural habitat

The results of the study of juvenile beluga before release into the natural habitat in the Volga-Caspian fishery basin in 2024 are presented in this paper. The relevance of the work lies in the need to obtain information about the physiological state of released juveniles, which is necessary to understand the possibility of fish adaptation to natural conditions. Growing conditions and fish-biological parameters of juvenile fish were studied and analysed. The size and weight parameters of fish and Fulton fatness are determined. Hydrochemical parameters during the period of beluga juvenile rearing were within the limits of values recommended for sturgeon rearing in pools of closed water exchange installations (CWE). As a result of statistical analysis of survival rate, size and weight indices of juveniles reared in 2024, it can be concluded that the fish breeding material was homogeneous and corresponded to the average long-term results obtained when rearing juveniles at the scientific and experimental complex of aquaculture “BIOS” under industrial conditions. The physiological condition of 10 g beluga juveniles reared in the conditions of UZV basins was assessed during the research. Lifetime blood sampling from the tail vein was carried out in order to study some physiological and biochemical parameters: hemoglobin, total serum protein, albumin, cholesterol, triglycerides, glucose, phosphorus. The results of the studies were statistically analysed and the variability of physiological and biochemical blood parameters in juvenile beluga whales was calculated. Beluga juveniles for research were obtained from the breeding stock included in the “Unique scientific installation” of the Russian Federal Research Institute of Fisheries and Oceanography “Bioresource collection of aquatic biological Resources”, released into a reservoir of fishery significance without pathologies, in satisfactory condition.

Effects of Flow Velocity on the Dynamics of Juvenile Fish Habitats in River Meanders of the Irtysh River

Effects of Flow Velocity on the Dynamics of Juvenile Fish Habitats in River Meanders of the Irtysh River

Sublethal Urea Exposure in Nile Tilapia: Morphological, Behavioural, and Histological Alteration.

The pace of research efforts has been extraordinarily accelerated across the globe to address the contamination issues caused by pesticides, and fertilizers, especially in the aquatic ecosystem. The sole aim of this study was to assess the effect of urea on Nile Tilapia (Oreochromis niloticus). For this purpose, the fish fingerlings were exposed to increasing concentrations of urea such as 0, 1, 2.5, 5, 10, 20, and 40 g/l for 72 hr. Survival analysis suggested a strong correlation between the increasing doses of urea and the mortality rate among tested fingerlings. This study reported remarkable morphological, and behavioural alternation such as increased operculum movement, bottom-dwelling, lethargy, secretion of mucus, reduction in food intake, and bleeding in the fin and around the mouth in the treated group. Haematological analysis revealed that a significant reduction in RBC count and Hb along with an increase in WBC number is associated with urea toxicity. Our study showed a significant rise in glucose concentration upon urea toxicity in Nile tilapia fingerlings for the first time, emphasizing the adverse effect of fertilizers on carbohydrate metabolism. Significant rises in the enzymatic activity such as alanine aminotransferase (ALT), alkaline phosphatase (ALP), and aspartate aminotransferase (AST) upon urea treatment emphasize the possibilities of liver damage, biliary obstruction, and abnormal glucose metabolism. Histological analysis of urea-treated fish compared to normal fish revealed that urea toxicity drastically altered the tissue architecture of fish's gills, eyes, intestine, and stomach. As the visual systems of mammals and fish resemble in more aspects, our findings may be useful in understanding the impact of pollutants on sensory organs concerning humans. We conclude that our findings highlight the importance of urea toxicity on Nile tilapia fingerlings and invite multidisciplinary research to uncover molecular mechanisms underlying urea toxicity.

Toxicogenomic signatures of estrogen-related modes of action in the zebrafish embryo.

Endocrine disruptors represent a diverse array of chemicals known to interfere with the endocrine systems of both human and environmental organisms, adversely affecting reproduction, development, and behavior, thus raising significant health and ecological concerns. Traditional regulatory tests for endocrine activity typically involve juvenile or adult fish, which is both time-consuming and resource-intensive and necessitates substantial animal use. This study adopts a transcriptomic approach to identify toxicogenomic signatures associated with the disruption of estrogen signaling in zebrafish (Danio rerio) embryos. Utilizing a modified zebrafish embryo toxicity test based on Organisation for Economic Co-operation and Development test guideline 236, the embryos were exposed to two sublethal concentrations of estradiol, bisphenol A, and fulvestrant. Despite no significant effects on survival or hatching rate observed in treated groups compared with the controls, our study effectively pinpointed several genes, including vtg1, cyp19a1b, fam20cl, sult1st2, pck1, agxtb, hsd17b12a, ptgs2a, and ccn1, as linked to a disruption of estrogen signaling. These genes emerge as promising biomarker candidates for identifying and distinguishing estrogen-related modes of action. Additionally, this approach not only supports the detection of potential endocrine disruptors but also opens up possibilities for prioritizing substances for higher tier endocrine testing, which could substantially reduce animal testing in the future.

Fish Meal Replacement by Chicken By-Product Meal in Diet: Impacts on Growth and Feed Availability of Juvenile Rockfish (Sebastes schlegeli), and Economical Analysis.

A 56-day feeding experiment was carried out to evaluate the effects of substituting fish meal (FM) with chicken by-product meal (CBM) in diets on the growth and feed utilization of rockfish (Sebastes schlegeli). Six experimental diets were formulated to be isonitrogenous and isolipidic. The control (Con) diet included 55% FM. In the Con diet, 10%, 20%, 30%, 40%, and 50% of FM was replaced with CBM, named as the CBM10, CBM20, CBM30, CBM40, and CBM50 diets, respectively. A total of 540 juvenile fish were distributed into 18 tanks (30 fish per tank and 3 tanks per diet) and fed to apparent satiation two times daily for 56 days. The weight gain and specific growth rate of rockfish fed the CBM10 and CBM20 diets were comparable to rockfish fed the Con diet. The feed consumption of rockfish fed the Con and CBM10 diets was significantly (p < 0.001) higher than that of fish fed all other diets, except for the CBM20 diet. However, protein retention, biometric indices, chemical composition, amino acid profiles, and plasma and serum parameters of rockfish were not significantly influenced by dietary FM substitution with CBM. The Con, CBM10, and CBM20 diets showed superior (p < 0.001) economic profit index (EPI) compared to the CBM30, CBM40, and CBM50 diets. Conclusively, FM up to 20% could be substituted by CBM in diets without impairing growth, feed availability, chemical composition, amino acid profiles, and blood parameters of rockfish grown from 2.5 g to 12.5 g. However, the long-term effects of CBM substitution or the potential use of combined CBM and other alternative protein sources for FM in rockfish diets are needed in future.

An evaluation of artificial floating littoral zones to support fish communities in reservoirs

Artificial water level fluctuations (WLF) in reservoirs impact fish communities by degrading littoral habitats. To mitigate these negative effects, artificial floating islands that mimic natural littoral zones appear as a promising mitigation tool. However, their effectiveness in supporting fish communities remains poorly documented. In this study, three artificial floating littoral zones (FLOLIZ, 70 m2 surface area) were installed in a French hydropower reservoir subject to extreme WLF. Fish communities were assessed in spring and summer over four years in FLOLIZ and in control littoral stations during daytime and nighttime. Fish, especially juveniles, did not appear more frequently in FLOLIZ than in control littoral stations during daytime. At night, both adult and juvenile fish were more abundant in the littoral zone of the reservoir. During the day, the fish community in FLOLIZ was mainly composed of juvenile Chondrostoma toxostoma and adult Perca fluviatilis. Differences occurred only for a few species and life stages (juvenile vs adult); however, in general, results indicated greater abundance or richness in control littoral stations. These results do not support the effectiveness of FLOLIZ in mitigating deleterious effects of artificial WFL. The distance of FLOLIZ to the littoral zone could explain these results. Further studies in different environmental conditions, in different ecosystems and with different FLOLIZ designs are needed to provide additional information on the effectiveness of such structures as a mitigation tool.

Effect of Astaxanthin on Blood Factors and Chemical Composition of Carp Cyprinus caprio

Astaxanthin dye was extracted from the Lobster shells to study its effect on the blood factors of common carp (Cyprinus carpio). mixture of organic solvents hexane and acetone (1:1, V/V) is used for Astaxanthin extraction. Extracted dye was added at 0.5, 0.10, and 0.15 mg/kg to four experimental diets that fed to common carp fingering for 60 days. The chemical composition of the control and experimental diet protein, fat, ash, and moisture content was 42, 6.2,7.5,7.13% respectively. Blood samples Parameters observed that the highest values observed in fish-fed diets with 150 mg/kg in blood factors PVC, BRC, and WRC were recorded at 36%, 1.45 106 mm3, 33.6 103 mm3, and 14 g/dl respectively compared to a control diet. It was concluded that supplementation of astaxanthin at 150 mg/kg increased the immune system in C. carpio. The scores for A, B, C, and D were 73%, 73.2%, 73.1%, and 73.1%, respectively. The results showed an increase in the protein, fat, and ash content were 18, 15, and 3% respectively, for fish fingerlings fed with astaxanthin at a rate of 0.15%.

Evaluation of the primary production and maximum fish production in Salman Farsi Reservoir, Fars Province, Iran

Primary production in water bodies corresponds to their fish production capacity. Aquaculture planning for water resources is conducted based on specific geographical conditions and their internal and external factors. Understanding the fish production capacity of lakes enables predictions for exploitation (fishing) and restoration of reserves. This research aims to estimate the primary production of the Salman Farsi Reservoir, Fars Province, on the Ghare Aghaj River, to evaluate fish production capacity and plan aquaculture development. Sampling was conducted to measure dissolved oxygen, water temperature, pH, conductivity, transparency, total phosphorus, total nitrogen, and chlorophyll-a in three transversal sections along the side, surface, and deep areas of the open water, with three repetitions in four seasons during 2023 – 2024. Trophic conditions were estimated using Trophic Status Index (TSI) models. Total production of the lake was calculated using the Brämick-Lemke and Koeschel models, while fish production was calculated using the Brämick-Lemke and Downing models. The annual average of dissolved oxygen, transparency, electrical conductivity, pH, total phosphorus, total nitrogen, and chlorophyll-a concentration in the lake was 8.2 ppm, 4.1 meters, 1387 μS/cm, 8.3, 0.174 ppm, 4.50 ppm, and 1.38 ppm, respectively. The average TSI based on transparency, phosphorus, chlorophyll-a, and Carlson’s index was 40, 78, 33, and 50. The initial production size in the lake was estimated 292 gC.m-²y-1. Fish production capacity was calculated based on primary production at 39 Kg.ha-1.y-1 and based on phosphorus at 33 Kg.ha-1.y-1, with an average of 36 Kg.ha-1.y-1. Considering the 2000-hectare livable area for fish in the lake, the total fish production this year was estimated at 71.8 tons. Under current lake conditions, the allowable fishing size was estimated to be 7 to 11 tons of fish per year. Determining the production capacity and trophic level can help maximize exploitation while minimizing ecological impacts and potential risks associated with restocking and fishing, such as the introduction of excessive juvenile fish into the lake.

Makna Leksikon Budidaya Tambak sebagai Representasi Kearifan Lokal dan Harmoni Ekologis Masyarakat Desa Wedani, Gresik: Kajian Antropolinguistik

The community of Gresik, particularly in Desa Wedani, has a rich lexicon related to fish pond cultivation. This study aims to: (1) describe the morphological formation process of fish farming lexicon in the local community; (2) analyze the structure and formation of phrases within the lexicon; (3) identify the cultural meanings and social aspects that influence the formation and usage of lexicon in freshwater fish farming in Desa Wedani. This research uses a qualitative descriptive approach with data collection methods including observation, interviews, and documentation. Data analysis employs semantic and anthropolinguistic analysis to understand the relationship between language, culture and social practices of the community. The findings show that the morphological formation process involves the addition of prefixes, such as ng-, ny-, and nj-, to base words to create active verbs referring to specific activities in fish farming. Lexicon data found include ngeduk (lifting soil at the pond's edge), nyingkal (tilling the soil to improve water circulation) and ngipuk (sifting to protect fish fry). The structure and formation of phrases within the lexicon demonstrate a close link between farming activities and the local language. The cultural meanings embedded in this lexicon reveal social values such as the community's attachment to environmental conservation and local wisdom in managing natural resources. The results of this study can enrich linguistic and anthropological language studies and support efforts to preserve local language and culture.

The benthic marine algae of the Maldives: historical insights into their diversity and distribution

Abstract In tropical ecosystems worldwide, benthic marine algae are important primary producers and habitat providers for many juvenile fish and invertebrate species. Calcified species are known to provide structural support to their respective communities, thus enhancing the overall system’s productivity. In the Republic of the Maldives, algae are an important yet currently poorly studied biological resource. We reviewed the literature around algal diversity and distribution across Maldivian atolls and compiled an extensive and updated taxonomic list. The list contains 353 species, of which 31 are Cyanobacteria, 26 Phaeophyceae, 109 Chlorophyta, and 187 Rhodophyta. Algal collections have been reported from 12 out of 20 atolls, and these mostly occurred during 20th century expeditions. The taxonomic status of 110 species has changed since first reported. While several species have been documented from the country, identifications have thus far almost solely relied on morphological assessments. Many of the reported algal groups require molecular confirmation. This suggests that benthic algal diversity from the Maldives is likely an underestimate. Since anthropogenic activities can significantly alter algal community dynamics, a baseline understanding of algal diversity is necessary to determine how such shifts affect the ecosystem as a whole, thus underpinning future management and conservation efforts.

Invasion stress mitigates climate stress in a brackish marsh amphipod

Abstract Organisms in coastal brackish ecosystems face not only highly variable environmental conditions, but the intensity and stochasticity of these environmental conditions are anticipated to increase due to climate change. While environmental changes are often presented unilaterally as stressors, there are some anthropogenic environmental transformations, such as the introduction of habitat forming plant species, that may mitigate physiological stress imposed by warming. In Suisun Marsh in the California Delta, native plant canopies allow light and heat to penetrate to the understory yet the canopies of the introduced Phragmites australis reed block out sunlight and heat for organisms living below. We set out to understand the physiological performance of mud‐dwelling invertebrates in this context: can invasion stress mitigate climate stress? We raised field collected Gammarus amphipods in the laboratory under simulated ‘native canopy’ and ‘Phragmites canopy’ temperature/light conditions based on data from our field environmental loggers. We assessed survival, body mass, fecundity, glycogen and protein content every 2 weeks from our lab population of amphipods. We found that amphipods raised under the Phragmites conditions had better survival, greater stores of protein, and similar body mass and stores of glycogen, which could positively impact available food resource quality for juvenile fishes. We support this with field data showing higher use of Phragmites canopies by amphipods, especially in the water column, across the year of sampling. Synthesis and applications: Understanding the potential benefits of Phragmites as climate stress refugia can inform management decisions around its mitigation in future restoration.

An Overview of the Freshwater Cladoceran Daphnia magna (Straus, 1820) and Its Application in Fish Larviculture

Over the last three decades, aquaculture has become increasingly important, leading to the commercial viability of various shellfish and finfish species. The production of live feed is gaining popularity as a way to enhance the nutritional quality of species raised in aquaculture. Daphnia is a type of small crustacean belonging to the Brachiopoda family, commonly found in freshwater environments. Daphnia spp. serves as an excellent natural food source for tropical fish fry and has emerged as an alternative to traditional fish feeds. Utilizing Daphnia in aquaculture offers benefits such as low cost and ease of cultivation. This study addresses the identification of Daphnia, its reproduction and life cycle, nutritional value, significance in aquaculture, and methods of cultivation.

Transcriptomic profiling of gill biopsies to define predictive markers for seawater survival in farmed Atlantic salmon.

Wild Atlantic salmon migrate to sea following completion of a developmental process known as parr-smolt transformation (PST), which establishes a seawater (SW) tolerant phenotype. Effective imitation of this aspect of anadromous life history is a crucial aspect of commercial salmon production, with current industry practice being marred by significant losses during transition from the freshwater (FW) to SW phase of production. The natural photoperiodic control of PST can be mimicked by exposing farmed juvenile fish to a reduced duration photoperiod for at least 6 weeks before increasing the photoperiod in the last 1-2 months before SW transfer. While it is known that variations in this general protocol affect subsequent SW performance, there is no uniformly accepted industry standard; moreover, reliable prediction of SW performance from fish attributes in the FW phase remains a major challenge. Here we describe an experiment in which we took gill biopsies 1 week prior to SW transfer from 3000 individually tagged fish raised on three different photoperiod regimes during the FW phase. Biopsies were subjected to RNA profiling by Illumina sequencing, while individual fish growth and survival was monitored over 300 days in a SW cage environment, run as a common garden experiment. Using a random forest machine learning algorithm, we developed gene expression-based predictive models for initial survival and stunted growth in SW. Stunted growth phenotypes could not be predicted based on gill transcriptomes, but survival the first 40 days in SW could be predicted with moderate accuracy. While several previously identified marker genes contribute to this model, a surprisingly low weighting is ascribed to sodium potassium ATPase subunit genes, contradicting advocacy for their use as SW readiness markers. However, genes with photoperiod-history sensitive regulation were highly enriched among the genes with highest importance in the prediction model. This work opens new avenues for understanding and exploiting developmental changes in gill physiology during smolt development.