BW has terrible nutritional value. Stick to BS and Mysis Shrimps. /QUOTE]
To say BW have terrible nutritional value is kinda simplistic -- true they don't have much in the way of vitamins or minerals, and yes they do have quite a bit of fat (not so bad for a growing young fish), but they have plenty of protein which growing fish can easily utilize:
The following results were done at "Riverina Laboratories" Albury, NSW, Australia and pertain to black worms, which nutritionally are nearly equivalent to blood worms
Crude Protein % as received..........................................................................54.52
Crude Fat % as received.................................................................................11.40
Crude Fibre% as received................................................................................0.20
Moisture % as received...................................................................................17.83
Solids % as received.........................................................................................82.17
Crude Protein % dry weight basis....................................................................66.35
Crude Fat % dry weight basis...........................................................................13.87
Crude Fibre % dry weight basis........................................................................0.24
Ocean Nutrition gives the following for their frozen blood worms.
Guaranteed Analysis
Crude Protein (min) 8.3%
Crude Fat (min) 1.2%
Crude Fiber (max) 3.9%
Moisture (max) 81.7%
(Protein as a percentage of dry matter - 45.3%)
Sure BS and Mysis Shrimp have better overall nutrition but there's nothing wrong with feeding a young Datnoid (or other fish) BW's, esp. if coming from a good and trusted source.
In fact a majority of Thai fish breeders & brokers, compromising a billion dollar industry here, feed their juvies heavily on blood worms -- but heck, what do they know? And I wouldn't doubt if it's much different in Malaysia, Singapore, Vietnam or Indonesia. Sure there are economic reasons likely involved, but nonetheless they turn out some pretty OK fish here on the whole, just saying.
Personally again though I would simultaneously try to get them on pellets at around 3" -- some might have an easier experience but hundreds of stories online will tell a different story when it comes to difficulty of getting (esp. bigger/older) Dats onto pellets, hence why many recommend an earlier the better approach.