(A) Botulinum toxin (BoTx) was expressed in post-mitotic neurons to inhibit neurotransmitter release in Tg(elavl3:Gal4-VP16); Tg(UAS:BoTxBLC-GFP) zebrafish. (B) Control and BoTx-positive fish were imaged at 80 hpf. (C) Body length measurements at 80 hpf, mean ± SEM, n = 17–20 animals. (D) Whole larva free glucose level measurements at 80 hpf, mean ± SEM, n = 30 batches of five larvae per replicate. (E–L) Whole mount immunostaining at 80 hpf for acetylated Tubulin (nerves), Insulin (beta cells), Somatostatin (delta cells), and DAPI (DNA). Maximum intensity projections are presented; A, anterior; D, dorsal; V, vagus nerve; P, pancreas; I, intestine. Quantification of islet nerve density (I), primary islet mass (J), beta cell number (K), and delta cell number (L), mean ± SEM, n = 14–16 animals, p-values from t tests are presented.