Osmotic distress: a probable cause of fish kills on exposure to a subbloom concentration of the toxic alga Chattonella marina

Chattonella marina blooms in a trophic gradient system: Interaction with environmental drivers

For coastal eutrophication, lots of studies focused on the influence from environmental factors, especially nitrogen and phosphorus, on algae blooms. The interaction between algae and environmental factors has been often ignored. Using Chattonella marina, a dominant species in marine algal blooms, we established a trophic gradient system that simulated C. marina blooms at three trophic levels: eutrophic, mesotrophic, and oligotrophic, and examined the life history patterns of C. marina and the interactions with environmental factors. Increased trophic levels influenced the growth potential of C. marina, while its unique cyst reproduction allowed it to thrive in nutrient-limited environments. Adequate nutrients caused changes in dissolved oxygen (DO) and pH led by C. marina, with the carbonate system playing a crucial role in regulating pH under nutrient-limited conditions. Limiting the growth of C. marina in areas with low nutrient by manipulating reactive silicate (SiO32-) availability may prove effective. Nitrate (NO3-) was the preferred nutrient for C. marina when its concentration exceeded that of ammonium (NH4+). Phosphorus played a crucial role in the growth and proliferation of C. marina, especially when other nutrients were scarce. The findings of this study may provide valuable insights into the effective management and prevention of algae blooms.

Removal of harmful alga, Chattonella marina, by recyclable natural magnetic sphalerite

Fish-killing harmful algal blooms (HABs) of Chattonella marina causes serious hazards and risks to fish farming and environment throughout the world. At present, it is necessary to explore cost-effective and recyclable materials for controlling C. marina blooms to reduce the cost and control the potential side effect to the environment. A novel earth-abundant natural magnetic sphalerite (NMS) for removing C. marina was systematically investigated, including the effect of NMS dosage, temperature, pH and salinity on algal removal efficiency. Algal cells could be rapidly removed by NMS (1-2g/L) through adsorption and physical interaction. The algal destruction process was enhanced under the following reaction conditions: temperature>25°C, salinity>30 ppt and pH value<7.5. The reusability of magnetic recycled NMS and effect of light irradiation on algal cell removal were also determined. NMS exhibited excellent stability after repeated algal cell removal, and the efficiency was further enhanced by light illumination. The current study suggested that using NMS to control C. marina blooms could be a novel promising strategy, which is cost-effective, stable, and easy for recycling.

Lethal effects of ichthyotoxic raphidophytes, Chattonella marina, C. antiqua, and Heterosigma akashiwo, on post-embryonic stages of the Japanese pearl oyster, Pinctada fucata martensii

The inimical effects of the ichthyotoxic harmful algal bloom (HAB)-forming raphidophytes Heterosigma akashiwo, Chattonella marina, and Chattonella antiqua on the early-life stages of the Japanese pearl oyster Pinctada fucata martensii were studied. Fertilized eggs and developing embryos were not affected following exposure to the harmful raphidophytes; however, all three algal species severely affected trochophores and D-larvae, early-stage D-larvae, and late-stage pre-settling larvae. Exposure to C. marina (5×10²cellsml^-1), C. antiqua (10³cellsml^-1), and H. akashiwo (5×10³cellsml^-1) resulted in decreased success of metamorphosis to the trochophore stage. A complete inhibition of trochophore metamorphosis was observed following exposure to C. antiqua at 5×10³cellsml^-1 and C. marina at 8×10³cellsml^-1. In all experiments, more than 80% of newly formed trochophores were anomalous, and in the case of exposure to H. akashiwo at 10⁵cellsml^-1 more than 70% of D-larvae were anomalous. The activity rates of D-larvae (1-day-old) were significantly reduced following exposure to C. antiqua (8×10³cellsml^-1, 24h), C. marina (8×10³cellsml^-1, 24h), and H. akashiwo (10⁴cellsml^-1, 24h). The activity rates of pre-settling larvae (21-day-old) were also significantly reduced following exposure to C. antiqua (10³cellsml^-1, 24h),C. marina (8×10³cellsml^-1, 24h), and H. akashiwo (5×10⁴cellsml^-1, 24h). Significant mortalities of both larval stages were induced by all three raphidophytes, with higher mortality rates registered for pre-settling larvae than D-larvae, especially following exposure to C. marina (5×10²-8×10³cellsml^-1, 48-86h) and C. antiqua (10³-8×10³cellsml^-1, 72-86h). Contact between raphidophyte cells and newly metamorphosed trochophores and D-larvae, 1-day-old D-larvae, and 21-day-old larvae resulted in microscopic changes in the raphidophytes, and then, in the motile early-life stages of pearl oysters. Upon contact and physical disturbance of their cells by larval cilia, H. akashiwo, C. marina and C. antiqua became immotile and shed their glycocalyx. The trochophores and larvae were observed trapped in a conglomerate of glycocalyx and mucus, most probably a mixture of larval mucous and raphidophyte tricosyts and mucocytes. All motile stages of pearl oyster larvae showed a typical escape behavior translating into increased swimming in an effort to release themselves from the sticky mucous traps. The larvae subsequently became exhausted, entrapped in more heavy mucous, lost their larval cilia, sank, become immotile, and died. Although other toxic mediators could have been involved, the results of the present study indicate that all three raphidophytes were harmful only for motile stages of pearl oysters, and that the physical disturbance of their cells upon contact with the ciliary structures of pearl oyster larvae initiated the harmful mechanism. The present study is the first report of lethal effects of harmful Chattonella spp. towards larvae of a bivalve mollusc. Blooms of H. akashiwo, C. antiqua and C. marina occur in all major cultivation areas of P. fucata martensii during the developmental period of their larvae. Therefore, exposure of the motile early-life stages of Japanese pearl oysters could adversely affect their population recruitment. In addition, the present study shows that further research with early-life development of pearl oysters and other bivalves could contribute to improving the understanding of the controversial harmful mechanisms of raphidophytes in marine organisms.

Sub chronic exposure to crude oil, dispersed oil and dispersant induces histopathological alterations in the gills of the juvenile rabbit fish (Siganus canaliculatus)

There is little existing information on the sub-lethal effects of experimental exposure of Arabian Gulf fish to oil pollution. This study investigated the potential sub-lethal effects of the water accommodated fraction (WAF) of light Arabian crude oil, dispersed oil and dispersant (Maxi Clean 2) on the gills of the juvenile rabbit fish (Siganus canaliculatus), observing several histopathological biomarkers at different time points and different doses. These laboratory exposures simulated a range of possible oil pollution events. Significant alterations in four health categories (circulatory, proliferative, degenerative and inflammatory) were identified and form the basis for understanding the short-term response of fish to oil. Evaluations of histopathological lesions in gill tissue were carried out following 3, 6, 9, 12, 15, 18 and 21 days of exposure. The main lesions observed and quantified were lamellar capillary aneurysms, vasodilatation of lamellae, hemorrhage, edema, lifting of lamellar and filamentary epithelium and epithelium necrosis, epithelial and chloride cell hypertrophy and hyperplasia, fusion of adjacent lamellae, epitheliocystis and inflammatory infiltration. Exposure of juvenile fish to WAF, dispersant oil and dispersant caused significant changes in the gill lesions and reaction patterns. Dispersed oil caused the most significant effect followed by WAF and then dispersant. The present study is one of the first which explores the relationship between oil pollution and epitheliocystis and reports that exposure to crude oil and dispersed oil increases the prevalence of epitheliocystis formation under controlled laboratory conditions.

Impact of laboratory exposure to light Arabian crude oil, dispersed oil and dispersant on the gills of the juvenile brown spotted grouper (Epinephelus chlorostigma): a histopathological study

The present study investigated the impact of subchronic exposure of the water accommodated fraction (WAF) of light Arabian crude oil, dispersed oil and dispersant on the gills of the juvenile brown spotted grouper (Epinephelus chlorostigma), observing several histopathological lesions at different time points and different concentrations. Significant alterations, compared to the control groups (p < 0.05), in four health categories (circulatory, proliferative, degenerative and inflammatory) were identified. Evaluations of histopathological lesions in gill tissue were carried out following 3, 6, 9, 12, 15, 18 and 21 days of exposure. The main lesions observed were circulatory (lamellar aneurysms, vasodilatation and hemorrhage), degenerative (edema, lifting of lamellar and filamentary epithelium and epithelium necrosis), proliferative (hypertrophy and hyperplasia of epithelial, mucous and chloride cells, fusion of adjacent lamellae), and inflammatory (lymphocytic infiltration). These results provide a tool for evaluating reclamation initiatives, such as the use of dispersants, and lead to better risk evaluations and environmental health in natural and reclaimed systems.

Unravelling the pathway of respiratory toxicity in goldlined seabream (Rhabdosargus sarba) induced by the harmful alga Chattonella marina

The harmful alga Chattonella marina has caused massive fish kills and economic losses worldwide. Suffocation is generally believed to be the major cause of fish death by C. marina. However, the specific mechanisms leading to respiratory disorder in fish and subsequent fish kills by C. marina remain unknown. The goldlined seabream, highly susceptible to C. marina, was employed to investigate temporal changes of physiological, histopathological and biochemical parameters related to respiratory function at different stages of exposure to C. marina. Hemoglobin oxidation and blood lyses were not found in goldlined seabream exposed to C. marina, which could not be the key reasons accounting for pO(2) drop in the stressed fish. Gill histopathology such as irregular organization of lamellae, mucous with algal cells trapped in interfilamental spaces, were typical in C. marina exposed fish. A surge of plasma lactate occurred in goldlined seabream shortly after exposure to C. marina (0.5h) and sustained throughout the exposure period, indicating rapid onset of and persistent anaerobic respiration in C. marina exposed fish. Depletion of plasma glucose was clearly evident in goldlined seabream showing stress symptoms and near death. Yet, fish alive in the C. marina bloom did not exhibit plasma glucose depletion. The results suggest that availability of fermentable fuel as indicated by glucose level is critical to determine fish survival in C. marina exposure. Overall, our findings have rebuked the involvement of hemolysins and/or nitric oxide as the culprits for C. marina toxicity to fish. This study is the first to demonstrate the pathway of respiratory toxicity induced by the harmful alga C. marina in fish.

Susceptibility of fish to Chattonella marina is determined by its tolerance to hypoxia

The harmful alga Chattonella marina has caused massive fish kills and economic losses worldwide. However, the fish kill mechanisms by C. marina have not been identified. The present study has confirmed that a significant elevation of blood osmolality is the universal response in moribund fish exposed to C. marina and the possible reasons leading to contradictory reports were identified. Both osmotic distress and respiratory impairment are important mechanisms leading to fish kill by C. marina. The susceptibility of marine fish to C. marina appears to be inversely related to their tolerance to hypoxia, with the hypoxia intolerant goldlined seabream being the most susceptible, and the hypoxia tolerant green grouper being the most tolerant to C. marina. Further studies in the marine medaka (Oryzias melastigma) showed that fish susceptibility to C. marina is directly related to susceptibility of the fish to hypoxia, but not related to its tolerance to hypersalinity stress.

The ichthyotoxic alga Chattonella marina induces Na+, K+ -ATPase, and CFTR proteins expression in fish gill chloride cells in vivo

Our previous studies demonstrated that the ichthyotoxic Chattonella marina stimulated proliferation of branchial chloride cell (CC) and induced osmotic distress akin to hyperactive elimination of ions in fish (Rhabdosargus sarba). To ascertain the in vivo effects of C. marina on key CC ion transporters, the localization and expression of Na(+), K(+)-ATPase (NKA) and cystic fibrosis transmembrane conductance regulator (CFTR) proteins in response to C. marina exposure were investigated, using a quantitative immunocytochemical approach. The polarized distributions of NKA (alpha subunit) and CFTR proteins in branchial CCs of R. sarba remained unchanged under C. marina exposure. However, significant inductions of these two ion-transporters were detected in CCs of fish after 6h exposure. By real-time PCR, no significant changes in gill NKA and CFTR mRNA expressions were detected, suggesting a post-transcriptional pathway is likely involved in regulating the ion transporters abundance. This study is the first to demonstrate the in vivo effects of harmful algal toxin on NKA and CFTR protein expressions in gill transepithelial cells. Taken together, an augmentation of branchial CCs together with hyper-stimulation of NKA and CFTR in CCs attribute to the rapid development of osmotic distress in C. marina susceptible fish.

Hydrogen peroxide is not the cause of fish kills associated with Chattonella marina: cytological and physiological evidence

Chattonella marina, a harmful algal bloom (HAB) causative species, was used to study the mortality, physiology, and pathology of a marine stenohaline fish, goldlined seabream exposed to the toxic alga. The median lethal time (LT50) was 3 h upon exposure to 8000 cells/ml of C. marina. Significant induction of filamental chloride cells (CCs) [i.e. increases in CC fractional area and in the volume density of CCs], concomitant with significant reduction of blood osmolality, were found in C. marina treated fish. To verify whether the toxicity of C. marina was mediated through oxidative stress, a hydrogen peroxide exposure experiment was carried out and the toxicity as well as cytological and physiological changes were compared with the C. marina treatment. Hydrogen peroxide at a concentration of 500 microM H2O2, (i.e. 25 times higher than that produced by 8000 cells/ml of C. marina (20 microM H2O2)) was unable to induce similar CC alterations and osmoregulatory impairment in fish as observed in the C. marina treatment. Non-specific membrane damage such as severe loss of microvilli projections on the CC apical opening and rupture of epithelial membranes in the lamellae were observed. The LT50 was 6 h, two times longer than that with 8000 cells/ml of C. marina. Based on the cytological and physiological evidence and toxicity data, the mechanism by which C. marina kills fish appears to be very different from that caused by H2O2/ROS. Osmoregulatory distress is the major cause of fish death upon exposure to C. marina.

The application of histo-cytopathological biomarkers in marine pollution monitoring: a review

During the past two decades, a variety of histopathological alterations in fish and bivalves have been developed and used as biomarkers in pollution monitoring. Some of these have been successfully adopted in major national monitoring programmes, while others, although show promise, are still in the experimental stage. This paper critically reviews the scientific basis, cause and effect relationship, reliability, advantages and limitations of 14 histo-cytopathological biomarkers. The usefulness and practical application of each biomarker have been evaluated against a number of objective criteria including: ecological relevance, sensitivity, specificity, dose-response relationship, confounding factors, technical difficulties and cost-effectiveness.