The optimization of copepod feeding protocol is paramount to improve culture productivity and to maintain favorable water quality parameters overtime, as well as saving operational costs by preventing the production of unnecessary quantities of microalgae. The influence of microalgal feeding concentration on major parameters related to culture productivity of the calanoid copepod Bestiolina similis (Paracalanidae) was investigated in a series of laboratory experiments. B. similis was fed eight different concentrations (0, 150, 300, 600, 900, 1,200, 1,500 and 1,800 μgC l^–1) of a mixed microalgal diet consisting of Tahitian strain of Isochrysis species, Pavalova 50 and Tetraselmis chuii at 1:1:1 carbon ratio. The results indicate that female daily and cumulative egg production over lifespan, egg hatching rate, naupliar and copepodite survival and development, adult female life expectancy, population growth and fecal pellet production rate (FPPR) were all significantly affected by microalgae feeding ration. Conversely, no significant influence could be established between microalgae food concentration and egg diameter or adult sex ratio. Feeding rations as low as 150 μgC l^–1 led to lower egg hatching rates, survival and development, adult female life expectancy and population growth compared with the higher microalgae rations tested. Feeding concentration ≤ 900 μgC l^–1 significantly limited female daily egg and fecal pellet production rate, as well as their cumulative egg production over lifespan, when compared to a level of 900 μgC l^–1. Bestiolina similis fed with 1,200 μgC l^–1 significantly improved female egg and fecal pellet production when compared to the lower treatments and was responsible for the highest female lifespan egg production and population growth observed among all treatments. Feeding rations as high as 1,500 μgC l^–1 and 1,800 μgC l^–1 did not lead to significant improvement in any of the parameters measured. This is likely due to a saturation effect at high food concentration which is known to decrease calanoid copepods feeding efficiency. Finally, B. similis FPPR, used as a proxy for ingestion, was found to saturate at a microalgae concentration of 783.4 μgC l^–1 using a non-linear Michael-Menton (2 parameters), indicating that CVI female ingestion did not increase significantly above this concentration. Based on the above results it is recommended that B. similis cultures should be fed at a concentration of 1,200 μgC l^–1, and not above, as rations > 1,200 μgC l^–1 will not significantly improve any of the productivity-related parameters observed in this study. Feeding rations should never be below 783.40 μgC l^–1 as this is the threshold level below which adult female ingestion rates become limiting.

Fisheries and Aquatic Sciences

The blood parrot cichlid (Cichlasoma citrinellum × C. synspilum), a hybrid of two distinct cichlid fish, is a popular ornamental fish. Its red appearance, achieved through its initial black coloration fading three weeks after hatching, is a key factor in its appeal. However, some juveniles retain their black or mottled skin. Despite its popularity, the molecular mechanisms underlying these color variations remain unclear. In this study, we compared the transcriptome profiles of fading and non-fading skin, identifying 167 differentially expressed genes. Non-fading (black) fish showed 88 up-regulated genes and 79 down-regulated genes compared to those in fading (white) fish. qPCR validated a subset of these RNA-Seq results. The enrichment analysis showed that these genes are associated with melanin production, the cAMP signaling pathway, and fatty acid metabolism. Genes related to eumelanin synthesis were up-regulated, while another synthesis pathway was down-regulated. Genes in the SLC and PDE families, linked to pheomelanin synthesis, were also up-regulated. Our findings suggest that the MSH-MC1R signaling pathway, the SCF/c-kit-Ras pathway, and the pheomelanin synthesis pathway play crucial roles in determining the development of black skin. These conclusions provide a theoretical framework for further research into pigment deposition and breeding albino varieties.

Background/Objectives: Aeromonas veronii is a significant pathogen affecting aquatic animals and has the potential to infect humans. Vaccination remains the most effective strategy for preventing infections caused by this bacterial strain. Methods: This study aimed to validate the efficacy of bacterial ghosts as an oral vaccine by administering them to Cyprinus carpio and evaluating the resultant innate and acquired immune responses. Following immunization, the vaccinated Cyprinus carpio were exposed to a lethal dose of the wild-type bacterial strain to assess survival rates and relative protection efficiency. Results: Oral vaccination with bacterial ghosts led to the significant enhancement of lysozyme (LZM) and myeloperoxidase (MPO) activity in koi serum. It also resulted in the upregulation of cytokines, such as IL-2 and TNF-α, as well as an increase in both systemic (IgM) and mucosal (IgZs) antibody responses. The immunized group demonstrated reduced cumulative mortality following bacterial challenge. The relative percent survival in the vaccinated group reached as high as 87.50%. Conclusions: The oral immunization of Cyprinus carpio with A. veronii-derived bacterial ghosts confers substantial immune protection, providing a foundational basis for the development of novel vaccines against A. veronii.

Tiger barb (Puntigrus tetrazona) is an economically important ornamental cyprinid widely cultured in the global aquarium trade; however, comprehensive information on its early development and reproductive performance remains limited. This study characterized embryonic development, larval and juvenile ontogeny, and reproductive performance under controlled hatchery conditions. Fertilized eggs were continuously observed from fertilization to hatching using stereomicroscopy, while larval development was monitored from hatching to 30 days post-hatching (dph). Reproductive performance was evaluated across five consecutive spawning cycles by determining estimated mean egg production per stocked female, fertilization rate, hatching rate, and larval survival. At 26.5–27.5 °C, embryonic development progressed through cleavage, blastula, gastrula, neurula, and organogenesis, and hatching commenced at 25 h 10 min post-fertilization; approximately 50% of viable embryos had hatched by 27 h 17 min, and hatching was completed by approximately 35 h 28 min. Newly hatched larvae measured 3.88 ± 0.56 mm in total length, and complete yolk-sac absorption occurred at approximately 7 dph. Characteristic vertical body pigmentation appeared at 15 dph, whereas juvenile characteristics were evident by approximately 20 dph, while complete scale coverage and adult-like coloration were observed by 30 dph. Reproductive performance declined significantly with successive spawning events, with fecundity decreasing from 182.33 ± 1.57 to 64.33 ± 3.52 eggs female⁻¹ between the first and fifth spawnings, accompanied by reductions in fertilization, hatching, and larval survival rates. These findings provide a morphological developmental reference and practical hatchery benchmarks that can support broodstock management, larval rearing, and seed production of tiger barb in ornamental aquaculture.