Tuf Voyaging - George R. R. Martin

Haviland Tuf is an honest space-trader (one of the few), and he likes cats. So how is it that, despite being up against the worst villains in the universe, he has become the proud owner of the last working seedship, pride of Earth's Ecological Engineering Corps?

We'll leave that aside for now - just be thankful that the most powerful weapon in space is in good hands, hands which now control cellular material for thousands of outlandish creatures.With his unique equipment and powerful spacecraft, Tuf is set to tackle the myriad problems that human settlers have created during their colonisation of far flung worlds. Hosts of hostile monsters, a population addicted to procreation, a dictator who is willing to unleash plagues to get his own way - and all that stands between the colonists and disaster is Tuf's ingenuity, and his reputation as an honest dealer in a universe of rogues ...