Dear Sairam,

a lot of methods. The Question is - what do you mean new? Majority are modification of elaborated 15-20 years ago, as they are based on some known achievements in technique. I’m attaching an article that can guide you into the problem (Perfect Reference of modern optical & other methods mainly for marine and deep waters):

Robert K. Cowen and Cedric M. Guigand - In situ ichthyoplankton imaging system (ISIIS): system design and preliminary results // Limnol. Oceanogr.: Methods 6, 2008, 126–132.

For my opinion some groups should process alive – like protistoplankton, and several taxonomic groups like Rotifers from zooplankton. Can propose you some new or improved ideas in calculation of individual mass (look in my site - From energy budget of small hydrobionts to the flow of energy through hydroecosystem. & Some Chapters like devoted to Individual mass are translated into English !).

As well may be necessary to pay some attantion to the special environment with turbidity (look attached book about Phytoplankton in Turbidity...).

Andrey

Robert K. Cowen and Cedric M. Guigand - In situ ichthyoplankton imaging system (ISIIS): system design and preliminary results // Limnol. Oceanogr.: Methods 6, 2008, 126–132.