Depth Distributions of Armored Catfish: Predator‐Induced Resource Avoidance?

Four species of armored catfish (Loricariidae) have size—specific depth distributions in a Panamanian stream, with larger fish in deeper water. Depth distributions do not change from the dry to the rainy season, despite a two— to three—fold increase in habitat area for larger loricariids. Throughout the year, standing crops of the loricariids' attached algal food are relatively high in shallow water, but decrease rapidly with depth. Over 2.1 yr, large Ancistrus spinosus, the most common pool—dwelling loricarriid, showed significant seasonal changes in somatic growth rates, with maximum rates in the early rainy season and minimum rates in the late dry season. Significant seasonal changes in mortality rates, estimated from rates of disappearance of marked individuals, were not detected. These data are consistent with the following hypothesis: small loricariids are limited, perhaps by predation, at densities below those necessary to deplete algae in shallow water. Larger loricariids avoid shallow water where they are vulnerable to fishing birds, even in the dry season when food is in short supply in deeper areas.