Peng Gao

Frozen mysid shrimp is the primary feed for farmed medicinal seahorses, yet no standardized storage duration exists, and whether storage-related feed changes affect the lipid-based medicinal quality of seahorses remains unknown. This study used targeted lipidomics to compare 98 lipid species across six lipid classes in three farmed seahorse species—Hippocampus erectus, H. abdominalis, and H. trimaculatus—fed mysid shrimp frozen for either 2 or 10 months. Prolonged storage did not cause a uniform decline in lipid quality; instead, each species exhibited a distinct response pattern. H. erectus showed compensatory increases in fatty acids, whereas phospholipids predominantly decreased; H. abdominalis exhibited broad attenuation across multiple lipid classes; and H. trimaculatus displayed an intermediate, class-dependent pattern. Notably, oxidized sterol derivatives declined consistently across all three species despite divergent fatty acid and phospholipid responses, suggesting that oxidized sterol derivatives may serve as candidate cross-species indicators of storage-related feed changes, although validation is required. Acylcarnitine profiles remained stable in H. erectus but decreased in the other two species, suggesting possible differences in lipid utilization among species. These preliminary results suggest that frozen-storage guidelines may need to be evaluated on a species-specific basis in future studies, with sterol monitoring as a candidate indicator for further evaluation.

Understanding niche differentiation and interspecific coexistence patterns of macrobenthos provides critical references for ecological assessment of bivalve aquaculture. Seasonal field surveys (Autumn 2023–Summer 2024) across 12 sampling sites were conducted in an intensive Meretrix meretrix tidal flat farm in Rudong, Jiangsu. Synchronous water depth, sediment grain size and total organic carbon (TOC), and salinity were measured at each station to characterize habitat gradients; no unfarmed reference tidal flats were included, so all community patterns only reflect within-farm variation. The study area has sustained 10-year continuous bottom culture with baseline juvenile stocking density of 250 ind./m² and twice-yearly manual harvesting. A total of 58 macrobenthic taxa were identified, and 13 dominant species were screened with a dominance index threshold Y > 0.02. All abundance data were fourth-root-transformed before Bray–Curtis community analysis to reduce bias of hyper-abundant taxa. Standardized Shannon niche breadth (0–1 normalized, r = 48 site–season composite units) and permutation-tested (999 replicates) Pianka niche overlap/similarity coefficients were calculated to quantify resource utilization similarity. Niche breadth ranged from 0.018 to 0.971, with farmed M. meretrix showing the maximum value, indicating broader seasonal resource adaptation. High niche overlap (>0.50) was detected between M. meretrix and four wild dominant species (Nephtys californiensis, Moerella iridescens, Lingula anatina, Umbonium thomasi). Notably, niche metrics derived solely from spatial abundance data cannot directly confirm interspecific competition or trophic segregation; the stable coexistence observed in our assemblage is tentatively hypothesized to be driven by vertical sediment partitioning and divergent feeding guilds based on published functional studies, without direct in situ trophic or stratified sediment evidence from this work. Hierarchical UPGMA clustering (0.35 Bray–Curtis distance threshold) and corrected NMDS ordination (48 site–season units, dominant-species fitted vectors) illustrated distinct functional groups. Based on the observed niche convergence among filter-feeding bivalves under local farming conditions, the range of 230–280 ind./m² is presented as an observational reference. Controlled manipulative experiments with gradient stocking densities are needed to test whether this range can balance aquaculture yield and benthic biodiversity.

Thermal elevation and residual chlorine pollution are two anthropogenic stressors that co-occur in estuarine waters affected by coastal power plant effluents. A 30-day exposure experiment was established with six treatment combinations comprising three temperatures (27 °C, 28 °C, and 30 °C) and two residual chlorine concentrations (0 mg/L and 0.02 mg/L) on Meretrix meretrix. Sampling was conducted on days 0, 10, 20 and 30 of the trial. The results indicated that elevated temperature (30 °C) significantly suppressed shell height and total body weight, while residual chlorine (0.02 mg/L) exerted time-dependent effects on shell length and width, with a significant interactive effect on shell length only at day 30. Crude lipid content declined with increasing temperature and residual chlorine exposure, whereas moisture and ash contents showed significant two-way interactions at all sampling time points. Intestinal amylase activity was continuously regulated by both stressors, with interactive responses on days 10 and 20, and was significantly suppressed under combined high temperature and residual chlorine stress. Collectively, we infer that combined exposure to elevated temperature and residual chlorine impairs shell growth, muscle biochemical composition and intestinal amylase activity of M. meretrix. Long-term experiments are required to further clarify the joint toxic effects of thermal stress and residual chlorine on the clam species.

Frozen mysid shrimp is the core feed for commercial seahorse aquaculture, yet quality deterioration caused by long-term cold storage severely constrains the survival and reproductive performance of seahorses. By integrating targeted metabolomics, physicochemical spoilage indicators, and 16S rRNA high-throughput sequencing, this study multidimensionally analyzed the stage-specific mechanisms of nutritional degradation and microecological deterioration of mysid feed at −20 °C under fresh (0 months), short-term frozen (2 months), and long-term frozen (10 months) conditions. The results demonstrate that short-term storage (2 months) effectively suppresses microbial-induced spoilage of mysids; however, freeze–thaw stress triggers cellular lysis, leading to a significant depletion of key water-soluble feeding-attractant amino acids, notably glycine and aspartate. In contrast, long-term frozen storage (10 months) induces severe lipid peroxidation and a massive accumulation of total volatile basic nitrogen (TVB-N). Microbiome analysis confirmed that the fundamental trigger for feed deterioration during the late storage stage is the explosive community succession of psychrotrophic specific spoilage organisms (SSOs), with Shewanella, Photobacterium, and Pseudoalteromonas emerging as the absolute dominant taxa. The highly active extracellular lipases and proteases secreted by these microbial communities extensively degrade the structural lipids of the feed, ultimately resulting in a paradoxical rebound in free fatty acid content during long-term storage. In summary, our research comprehensively details how freezing compromises diet quality through specific biological and chemical pathways. This establishes essential scientific groundwork aimed at refining commercial preservation techniques, executing precise dietary enrichments, and ultimately securing long-term viability across the captive Hippocampus breeding sector.