Environmental regulation of sexual maturation and reproduction in tilapia

Impacts of climate change on fish hatchery productivity in Bangladesh: A critical review

Bangladesh is among the countries most vulnerable to climate change due to its geographical location. Climate change issues have become major concerns in aquaculture industry, particularly for fish hatchery productivity. Fish production in Bangladesh is mainly steered by the aquaculture sector, which is dependent on private hatchery-based fish seed production to a great extent. This review aimed to present the impacts of climate change on fish hatcheries, particularly during different stages of hatchery production, and the economic loss from the onset of disease and other impairments due to environmental causes. Geographically, most hatcheries in Bangladesh are operated within a narrow range of temperature (22.8-23.1 °C, equivalent to 73-73.5 °F) and rainfall (1750-2000 mm). Thus, slightest fluctuations in these parameters affect seed production in fish hatcheries. The broodstock, produced in natural and captive conditions, is severely affected by flash flooding, water quality deterioration, river siltation, erratic rainfall, and temperature fluctuations. Based on our review, temperature fluctuation is the main factor hampering maturation and breeding performances of broodstock. Temperature has also been reported to affect embryonic development and cause stunted growth of larvae and juvenile. In shrimp and prawn hatcheries, fluctuations in temperature, pH, and salinity are responsible for post-larval disease outbreaks. In some instances, storms and heavy rainfall wash away reared broodfish and fish seed from the hatcheries, causing massive socioeconomic losses. This review presents indisputable negative impacts of climate change on hatchery production. As of now, no cost-effective proven strategies have been developed to minimize the effects of climate change on Bangladesh's fish hatchery production, on which the aquaculture industry is inextricably dependent. For sustainable fish hatchery production, basic research on climate impacts on hatcheries is inevitable, as well as improving capacity of hatchery owners are needed for resilient hatchery operations in Bangladesh and similar environments worldwide.

The attraction trick: males in early stages of disease become more chemically attractive to Nile tilapia (Oreochromis niloticus) females

In aquatic systems, olfaction plays an important role in acquiring information about the social environment and influences important behaviours in various contexts, including predator avoidance, foraging, aggressive and reproductive behaviour and mate selection. As the presence of diseases might modify individual odour, fish may use the variability in conspecifics' odours as an indicator of the health status and infectious load of potential mates. Here, female Nile tilapia were tested for their ability to detect infected males and discriminate between bacterial infected and uninfected individuals by means of chemical cues. Females were allowed to choose between the odours of males infected by Aeromonas hydrophila bacteria and uninfected males. The findings show that female Nile tilapia initially showed a preference for infected males in terms of their first choice in a dichotomous choice test, but the total duration of time spent with the stimulus from infected males was not longer than that for the uninfected males. This may indicate that males at early stages of infection, i.e., without advanced clinical signs of infection, emit odours that allow them to enjoy the benefits of socialization when the infection is not yet detected by conspecifics. Thus, in the context of reproduction, males might attract female partners and have some chance of reproducing, before being avoided.