Environmental contamination of ecosystems, leading to their eventual degradation, can result from various sources, including agricultural, industrial, and municipal runoff. This poses a significant threat to Mexico’s rich biodiversity. Pollutants from runoff alter water chemistry, notably by disrupting pH balance, which can impact the ornamental fish trade. One species particularly vulnerable to such environmental changes is the Mexican orange dwarf crayfish (Cambarellus patzcuarensis), which is endemic to Michoacán. Though currently listed as endangered, it has become a popular ornamental species. Gaining a better understanding of how environmental stressors affect ornamental species is crucial to improve production practices.
Due to the precarious status of C. patzcuarensis, we utilized calico crayfish (Faxonius immunis) as a proxy species for our experiments. Both species live in comparable water conditions (pH of 6.5 to 8.0 and temperatures between 20 and 29 °C) inhabiting sandy or muddy environments, and unlike C. patzcuarensis, F. immunis is not threatened or endangered. To test the effect of lowered pH on ornamental crayfish, we exposed 48 calico crayfish to one of four pH treatment ranges (4.5-5.0, 5.0-5.5, 5.5-6.0, or 6.5-7.0). Individual crayfish were stocked into 18-liter tanks in one of four small RAS (12 tanks/RAS). Each RAS had a total volume of ~379 liters and was fitted with mechanical and biological filtration as well as UV-sterilization to maintain water quality. RAS were randomly assigned to one of the four pH treatment ranges, and pH was adjusted by adding muriatic acid (31.45%) every other day until target pH levels were reached. Crayfish are being maintained in the RAS for six months. During this time, they are being fed a diet of sinking algae pellets. Animals will be measured every four weeks for total length, carapace length, and weight. Additional observations will include post-molt malformations and ability to molt into a sexually mature form (males = Form 1: females = mature annulus ventralis & glair activity).
Prolonged exposure to acidic or alkaline pH can significantly impact the availability of essential ions, such as calcium, which are vital for F. immunis to absorb. Calcium is crucial for healthy exoskeleton formation, and disruption in its availability can lead to deformations. It is hypothesized that F. immunis exposed to low pH levels (below 7.0) will exhibit abnormal exoskeleton development, potentially impeding growth and the ability to molt into a reproductive state. Conversely, F. immunis maintained at a pH closer to neutral ( 7.0) are expected to display normal growth and better survival. Therefore, maintaining an optimal pH range within aquaculture and natural systems may be essential for species’ health and reproductive success.