Oxytocin modulates social preference and anxiety-like locomotor behavior in albino and non-albino zebrafish.

Socio-emotional and exploratory behaviors in zebrafish (Danio rerio) are shaped by conserved neuromodulators such as oxytocin (OXT), yet phenotypic variation (e.g., albinism) may modify sensitivity to OXT-dependent regulation. Here, we tested whether pigmentation phenotype alters behavioral responses to acute OXT across structured social and anxiogenic contexts. Adult albino (A; n = 30) and non-albino (N; n = 30) zebrafish (total n = 60; equal allocation across 6 groups, n = 10/group) were exposed to OXT by immersion (33.2 ng/mL, 15 min) under a 2 × 3 factorial design (Phenotype × Dosing regimen: Vehicle; OXT single exposure assessed at 24 h; OXT repeated exposure assessed at 48 h) and evaluated using the social preference test (SPT), social interaction (SI) test, and novel tank test (NTT). In the SPT, decision-zone occupancy and mean distance to the non-social arm were robustly modulated by dosing (p < 0.0001; p = 0.007) without phenotype × dosing interactions; locomotor outputs (swimming distance, p = 0.040; velocity, p = 0.041; counterclockwise rotations, p = 0.006) also showed dosing effects only, supporting a dissociation between social allocation and global motor output. In the SI test, stimulus-zone occupancy showed a significant main effect of phenotype (p = 0.009), independent of dosing, and locomotor indices similarly exhibited phenotype effects without interaction (swimming distance and velocity, p = 0.017; mobile-state duration, p = 0.002). In contrast, the NTT revealed phenotype-dependent locomotor regulation: highly mobile duration showed a significant interaction (p = 0.002) with strong main effects of phenotype and dosing (both p < 0.001), while immobile duration displayed an interaction (p = 0.015) and dosing effect (p = 0.005), driven primarily by the non-albino phenotype; clockwise rotation (p = 0.018) and active-state duration (p = 0.030) further indicated phenotype-related differences. Collectively, OXT exerts context- and dosing-regimen-dependent modulation in zebrafish, with social allocation primarily dosing-driven and largely phenotype-independent, whereas anxiety-related locomotor dynamics show marked phenotype specificity.