To assess the dependence on fish consumption of families and its impact on nutritional status and neurodevelopment of pre-school children.

Cross-sectional study that measured children’s hair mercury (HHg) as an indicator of family fish consumption, growth (anthropometric Z-scores, WHO standards) and neurological (Gesell developmental scores (GDS)) development.

Traditional living conditions among families residing in the area adjacent to the Samuel Dam (Western Amazon) hydroelectric reservoir.

Two hundred and forty-nine pre-school children (1–59 months of age) from families transitioning from the traditional Amazonian lifestyle.

Family fish consumption was significantly correlated with children’s HHg concentration (Spearman’s r = 0·246, P < 0·0001); however, HHg had no significant association with growth (Z-scores). Overall, the prevalence of severe malnutrition, i.e. stunting (height-for-age Z-score (HAZ) ≤ −3), underweight (weight-for-age Z-score (WAZ) ≤ −3) and wasting (weight-for-height Z-score (WHZ) ≤ −3) was 5·2 % (n 13), 0 % and 0·8 % (n 2), respectively. The prevalence of moderate stunting (HAZ ≥ −3 to ≤ −2), underweight (WAZ ≥ −3 to ≤ −2) and wasting (WHZ ≥ −3 to ≤ −2) was 8·8 % (n 22), 2·4 % (n 6) and 4·8 % (n 12), respectively. Although 76 % of the children showed adequate GDS (>85), multiple regression analysis showed that fish consumption (as HHg) had no impact on GDS, but that some variables did interact significantly with specific domains (motor and language development).

The study showed that the families’ shift in fish consumption had no negative impact on the growth of young children and that ensuing methylmercury exposure has not been a noticeable neurodevelopmental hindrance.