A model of fish distribution in rivers according to their preference for environmental factors

Coexistence of Two Closely Related Cyprinid Fishes (Hemiculter bleekeri and Hemiculter leucisculus) in the Upper Yangtze River, China

Species coexistence is one of the most important concepts in ecology for understanding how biodiversity is shaped and changed. In this study, we investigated the mechanism by which two small cyprinid fishes (H. leucisculus and H. bleekeri) coexist by analyzing their niche segregation and morphological differences in the upper Yangtze River. Morphological analysis indicated that H. leucisculus has posteriorly located dorsal fins, whereas H. bleekeri has a more slender body, bigger eyes, longer anal fin base, and a higher head. Niche segregation analysis showed spatial and trophic niche segregation between these two species: on the spatial scale, H. leucisculus was more widely distributed than H. bleekeri, indicating that H. leucisculus is more of a generalist in the spatial dimension; on the trophic scale, H. bleekeri had a wider niche than H. leucisculus. Therefore, these two species adopt different adaptation mechanisms to coexist

A model of fish preference and mortality under hypoxic water in the coastal environment

Eutrophication and associated occurrence of hypoxic condition could cause significant damage to marine ecosystems, resulting in considerable economic losses to fisheries and aquaculture and is a major source of stress that fish often have to contend with in order to survive. This problem is likely to be exacerbated in the coming years, since the wastewater treatment facilities is unlikely to catch up with increasing human activities. Moreover, large-scale reclamation projects in coastal areas have recently been increased, and these activities certainly have adverse impacts on water quality and fisheries resources. Coastal construction has a significant role in the development of hypoxic water by changing the current and mixing pattern of water. Changes in species composition and decreases in species richness and diversity have been well documented in hypoxic systems. Hypoxia could cause endocrine disruption in fish and eliminate populations of sensitive species. Shallow coastal areas are of great importance for the special nursery of fish and shellfish and land reclamation in these areas cause strong damage to fisheries. Although the tolerance of aquatic life to hypoxia is known, there is no information about the mortality of fish caused by hypoxia because fish can swim around it and no modeling study has yet been carried out. Criteria that influence the movement of fish are: amounts of food, water temperature and depth, dissolved oxygen concentration and nature of seabed. However, among these, water temperature and dissolved oxygen are the most crucial parameters that affect survival, movement and growth of fish. In this paper, a model of fish preference and mortality for environmental conditions was developed and applied to the Hakata Bay where hypoxic water occurs every summer. For the purpose of this study, a field survey of fish behavior under hypoxic water was conducted by releasing marbled sale (Pleuronectes yokohamae) in the inner bay. Moreover, a series of preference tests for DO, salinity and temperature in the laboratory were conducted in order to decide preference parameters of fish. Using the results of both field and laboratory studies, a sub-module of fish preference and mortality was coded within an integrated hydrothermal and eutrophication model (CHEM) to predict the behavior and mortality of marbled sale when hypoxia would occur in the bay. The model could reasonably simulate the behavior of the fish under hypoxia. An assessment of the impact of the ongoing land reclamation project of about 401 ha in the Wajiro tidal flat zones at the head of the bay on the fisheries resources was also conducted using the model. The results showed that the artificial land lowered the mortality rate of fish under hypoxic condition in the bay during the summer period.