Big enough to be a neighbour, not a meal
Young bumblebee gobies are ready for the main tank when they have grown beyond the size an adult goby or larger tankmate could swallow in one attempt. Adult bumblebee gobies are small fish, but they are opportunistic, and a tiny juvenile hopping across open sand makes an easy target. Judge by body thickness and length against the adults in the actual receiving tank, not by a general age, because growth in a well-fed rearing setup can outpace a sparse one. The young fish should look sturdy, with clear banding developing and a rounded belly from regular feeding, rather than thin and translucent. A juvenile that still appears fragile belongs in the rearing tank until it has the bulk to hold its own.
Territories must exist before the fish do
In young bumblebee gobies, the move succeeds or fails on shelter. Adult gobies each defend a small area around a chosen cave, shell, or rock crevice, and a newcomer with nowhere to claim will be chased from one defended spot to the next until it exhausts itself. Before moving any young fish, add more caves, shells, tubes, and rock nooks than there are gobies in total, spread across the tank floor so each fish can settle out of the others' direct line of sight. Rearranging some existing decor at moving time can also soften the adults' sense of ownership, giving newcomers a fairer chance to settle. Several young fish introduced together spread attention better than a single arrival facing every resident alone.
Matching the brackish water exactly
Young bumblebee gobies raised in brackish conditions must move into water matched closely to what they already live in, because a sudden change in salinity stresses small fish far more than the short journey between tanks. Measure the rearing water and the main tank, bring them into line gradually beforehand if they differ, and acclimate the young fish slowly rather than tipping them straight in. Temperature, cleanliness, and feeding routine should also carry across, so the only new challenge on moving day is the social one. Keep the receiving tank's other residents in mind as well: larger brackish tankmates that mouth at bottom fish are a reason to delay, even when adult gobies themselves would accept the youngsters.
Settling signs in the first week
For young bumblebee gobies newly among adults, success looks like each young fish holding a perch, emerging to pick at food, and showing only brief, low-level disputes that end with one fish retreating unharmed. Constant chasing, a youngster trapped at the surface or in a top corner, or one that stops eating means the arrangement is failing and that fish should return to the rearing setup. Offer food across several spots on the floor so subordinate fish can eat away from defended caves, and check after dark with a dim light if a shy individual never appears at daytime feeds. Note which shelter each newcomer claims, because a fish that keeps changing spots is still being displaced. Tracking those claims and feeding spots in KinsLe with Care Teams lets helpers spot a displaced youngster quickly and adjust shelters before it loses condition.