Phytoplankton and periphyton in ponds with Nile tilapia (Oreochromis niloticus) and bocachico (Prochilodus magdalenae) Fitoplancton y perifiton en estanques con tilapia nilótica (Oreochromis niloticus) y bocachico (Prochilodus magdalenae) Fitoplancton e perifiton em viveiros com tilapia nilotica (Oreochromis niloticus) e bocachico (Prochilodus magdalenae)

Background: phytoplankton is considered the most important community in the aquatic food chain. As the basis of the food chain, periphyton offers possibilities for further optimization of extensive aquaculture ponds, although in-depth research on its effects on phytoplankton is necessary. Objective: a test was conducted to assess periphyton effects on phytoplankton concentration (org/L) and Shannon Weaver algae diversity index (DI). Methods: 18 earthen ponds (90 m2) under extensive polyculture conditions and low stocking density (2 kg/m2 at the end of the culture) were used. Fish density was 2.6 Nile tilapia/m2 and 0.7 bocachico/m2. Treatments consisted in the inclusion or absence of substrate (polyethylene pipes) for periphyton attachment (B1 for substrate presence and B2 for substrate absence) combined with three feeding strategies: no balanced feed offered (A1), 20% crude protein feed (A2), and 25% crude protein feed (A3). The combination of substrate levels and feeding strategies resulted in six treatments. Each treatment was replicated there times using a randomized complete block design for a six-month experimental period. Data were analyzed using a repeated-measure ANOVA in which time appears as a third factor (monthly samplings). Results: an interaction between factor B and time was found (P < 0.05), suggesting that the DI was significantly higher in ponds with substrate (B1) at given times (times 3, 4, 5 and 6). A significant interaction was also found between factors A*B*time (P < 0.05) for the concentration of organisms; resulting in a higher concentration of organisms in treatments that included substrate for periphyton attachment. Conclusion: periphyton had a positive influence on phytoplankton development, which is why stimulating periphyton attachment on an artificial substrate is a good way of improving a pond's primary production. Antecedentes: se considera que la comunidad fitoplanctónica es la más importante en la cadena alimenticia acuática. El perifiton, como base de la cadena alimenticia, ofrece posibilidades que optimizarían el uso de los insumos utilizados en sistemas extensivos, pero es necesario investigar a fondo sus efectos sobre el fitoplancton. Objetivo: evaluar el efecto del perifiton sobre la concentración (org/L) y el índice de diversidad algal Shannon Weaver (DI) del fitoplancton. Métodos: se realizó un ensayo en 18 estanques en tierra, de 90 m2, bajo condiciones de policultivo de baja densidad de siembra (buscando alcanzar máximo 2 Kg/m2 al final del cultivo) con 2,6 tilapias y 0,7 bocachicos/m2. Los tratamientos consis