Ours is a Canon 450D bought from Harvey Norman's in their after Christmas sale about 4 years ago. Came with a 2 lens kit. Grant uses the 18 - 55mm most of the time as it's good for all round general photography. Also have 55 - 250mm lens which also does a good job for what are basically cheap lenses. Both have image stabilisation.
He has a 60mm macro lens which he doesn't use much but if you do want to do any macro photography, it's a must.
The 450 (I think the current model is now a 600) he finds to be a good one step above entry level DSLR. If you want a faster camera which would be most beneficial when trying to photograph fish, choose one with a full sized sensor as they are more sensitive and produce less noise. Sensitivity and noise level is more important than number of pixels. Often as they increase the number of pixels, but don't increase the size of the sensor, the background noise and sensitivity suffers.
The higher the sensitivity (ISO number) the more sensitive the camera will be in low light. Also, a lens with a higher speed will be much more suitable in low light. Fish in a tank always suffer from low light levels. The image stabilisation allows you to run a longer shutter speed in low light so allowing better pics of the fish. It is all a compromise between shutter speed, aperture and ISO settings depending on depth of field required and how fast the object is moving.
Grant bought a Canon because he likes their products, the price was right, and reviews generally were favourable. He would be more than happy with a Canon or Panasonic (or several others), it all depends on personal choice. Once you start with one brand of camera, you will probably stick with it because the lenses you buy will probably fit whatever you upgrade to.
I love my old Sony (it was bought in 2004) but it is starting to have problems. It was really fast when I bought it but now seems so slow compared to the cameras of today! :roll: