Do you have a Lumion license now? It’s quite expensive if you go with the full library of assets so that may factor into your costs. A few other things to consider:
Market - Depending on where you live or your client is based, there could be a budget range depending on the cost of living/labor in that area. Rendering firms in Los Angels or London UK would likely bill higher than other areas where labor is cheaper. Of course the internet has made things more competitive as now a firm in LA could easily hire a renderer in China at potentially lower expense.
Client - Does the fishery client have a decent budget? Have you worked with them on other projects. Are the demanding or easy going? These all can add time to the project and time = money.
Detail / Quality - Have then sent you anything as a comparable so you know the level of detail you need to achieve? Even in Lumion, it takes time to set materials, plants (as you noted), entourage lighting, high res exporting, etc.
Fixed rate vs Hourly - consider how much time you think each view will take and estimate the total hours at your desired billing rate. You can set the terms in the contract as to the number of revisions, etc to help manage expectations as clients tend to ask for more without necessarily agreeing to ‘add services’. A fixed cost per view is preferred. Keep in mind that an aerial render may take more time than say a close up ground level so consider pricing aerials higher.
Modeling effort - be sure to factor the modeling effort in addition to the rendering. This can be lumped in to the total hours estimated for your fixed fee amount or separate out so the client understands how much each task costs them and can make decisions about where to spend more money - on the modeling side or the rendering/post production side. Note that quite a few renderers don’t do major modeling and require a model be provided by the client.