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The bristlenose pleco (Ancistrus cirrhosus) is a species of armored catfish in the Loricariidae family that breathes air facultatively when the aquatic environment becomes hypoxic. The bristlenose pleco uses its highly vascularized stomach as an air breathing organ. The two main goals of this developmental study were to determine the size of onset of air breathing and to determine the frequency of air breathing behavior in bristlenose plecos from juveniles to adults. Developing juveniles reach functional maturity within four to six months of hatching and grow to an adult size of eight to ten cm in length. To examine the developmental timing for the onset of air breathing, we tested different sized juveniles beginning at one cm up until 8 cm in length. The developmental timing for the onset of air breathing was measured by exposing each fish to a slowly decreasing aquatic oxygen content from 100% air saturation down to 8% air saturation. Fish were first able to breathe air at just over 2 cm and 1 gram in mass. There was a weak negative correlation between fish length and % air saturation at which air breathing began. When exposed to 15% air saturation, frequency of air breathing was negatively correlated with fish length. Armored catfish are becoming an invasive species in the southern US, outcompeting local fauna potentially because of this adaptation. This research provides important insight into the development of the air breathing adaptation that may allow these fish to outcompete the others.

Species invasions provide a n excellent opportunity to ask important ecological questions and test the effects of individual species on ecosystem structure and function. In both terrestrial and aquatic ecosystems, non-native grazing organisms alter the quality and quantity of food resources and affect nutrient storage and cycling. Low-trophic position species, such as herbivorous and detritivorous fishes, have been introduced and become established in aquatic ecosystems throughout the globe and these species can fundamentally change community st ructure and ecosystem processes. In Chiapas, Mexico I quantified the effects of non-native armored catfishes (Siluriformes: Loricariidae) on ecosystem structure and function. Loricariids are grazing fishes that have been introduced to many freshwater ecosystems outside of their native range due to their popularity in the aquarium trade. The purposes of this study were threefold. Initially, I examined the effects of loricariid grazing on the quality and quantity of basal food resources. Secondly, I investigated the top-down and bottom-up pathways by which loricariids affect algal biomass and gross primary productivity by quantifying the net effects of grazing and nutrient remineralization. Lastly, I examined whether loricariids are important drivers of nutrient dynamics and estimated whether they function as a source or sink of nutrients in invaded stream reaches. The results from this study indicate grazing by loricariids reduces the quality and quantity of benthic resources and this negatively influences higher trophic levels. Additionally, intensive grazing by high-densities of loricariids result s in a negative net-effect on algal biomass and primary productivity in the Chacamax River. At a larger spatial scale, my findings suggest loricariids dramatically increase the amount of nutrients stored in fish tissue and the rate at which nutrients are remineralized via fish excretion, thereby converting the river to a system where fishes are primary drivers of nutrient dynamics. This study also demonstrated invasive organisms can simultaneously function as sources and sinks of nutrients and these effects are element-dependent. Finally, this investigation highlights the importance of quantifying the consumptive and remineralization effects of invaders to develop a comprehensive understanding of how non-native organisms influence ecosystem structure and function in invaded ecosystems.