The pond in my garden attracts a myriad of insect life, such as this moth I found on a pond plant (Ornduffia albiflora) today. The pond has small fish to eat any mosquito larvae and stop mosquitoes breeding. When I first dug out the pond I hoped water movement from the water filter would be enough to deter mosquitoes breeding, but I needed biological control. I got White Cloud Mountain minnows (Tanichthys albonubes)* and later added Western Pygmy Perch (Nannoperca vittata) which are native to waterways in WA.
The numbers have fluctuated over the years, and there are currently more Pygmy Perch than minnows but they happily coexist. In summer the Pygmy Perch breed and there’s individuals of different sizes as they grow. Every now and then I find a dead adult and this week one was sick, having difficulty diving and unable to angle at the surface to feed. I first got Pygmy Perch in 2010 so these deaths are probably from old age (although I don’t know their lifespan).
I have trouble taking photos of the fish because I don’t have an underwater lens, but the sick fish couldn’t leave the surface and I could take photos. I felt bad taking advantage of fishy’s infirmity, but karma got me when I dropped my phone in the water! (It’s all dried out now and working fine.) By the end of the day the sick Pygmy Perch was dead and I buried the body next to the pond, to add nutrients to the surrounding native plants.
I noticed sick fishy’s predicament because I was weeding one of the pond plants that tries to take over. Every year I have to remove most of the Baumea preissii, but now Marsilea drummondii (Nardoo) is joining the race to cover the pond surface. I don’t mind this. Letting them grow, then removing large amounts of these plants makes for an ever changing habitat for the fish, tadpoles and sometime frog visitors that enjoy the macroinvertebrate and insect life attracted to my pond.
The most noticeable macroinvertebrate in my pond are freshwater snails.  They look similar to the native aquatic snails we collected and identified from Lake Joondalup in my conservation course. My pond snails arrived on a pond plant from a chain nursery. This summer their numbers have increased a lot and they may be an introduced species. I need to get Davis & Christidis’ A Guide to Wetland Conservation of Southwestern Australia from the library to check their identification. 
* White Cloud Mountain minnows are native to China and extinct in the wild but are widely available in the aquarium trade. A feral population of White Cloud Mountain minnows was found in NSW, most likely the result of fish being washed out of backyard ponds during heavy rains. My garden location isn’t prone to flooding, but in areas where this is a consideration, only native fish species should be stocked.
- Water and Rivers Commission (2001) Water Facts: Water quality and macroinvertebrates.
- Davis & Christidis (1997) A Guide to Wetland Conservation of Southwestern Australia Perth: WA Museum.