We have very strict laws about fish and so forth to prevent any diseases and even over population of various animals and plants. We have been trying for the last 100 years or so just to get rid of a plant that was brought over here by the Europeans. Its taken over so badly that there are lots of areas where the natural plants have died because of it.
Remember in south africa we almost have more nature reserves and wildlife parks than anything else. In Cape Town where I live we have a indigineous plant life that can only be found here. Fynbos is what its generally called, and its stunningly amazing. So we all work hard to protect all our plant life and animal life. Where I live im about 2 blocks away from a nature reserve.