So you made something without a target plan in mind?
Are your 50 videos tied in a progressive, coherent theme like a TV episode or are they just a random selection of topics?
Is the content and narration formatted in a documentary/national geographic style or is it just a bunch of footage maybe put to some music?
Why did you choose to make 50 25 minute videos rather than a single or a few couple hour videos?
In short, who specifically would want to watch them and why? Then your next question is where do those people look for that content? There are many distribution channels for many types of content. Too many to capture them all.
You could pitch cable companies, but you need much more of a hook than what you gave us, "a series of videos that deal with matters of biology, especialy insects and spiders".
You might see interest at national geographic or discovery, except shooting on minidv cameras will likely disqualify you even if they liked your pitch.
What might be more effective is contacting biology, insect and arachnid departments at colleges and highschools around the world and seeing if they'd pony up for a copy.
Cory
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Cory Petkovsek
Corporate Video