Draftsman plot

— to evaluate relationships between every pair of variables in multivariate data efficiently

Interrelationships among contributions of different food sources to dominant herbivorous fish.

• Fish food contribution was positively related to sediment contribution.
• The growth of phytoplankton was limited by nutrient levels, especially phosphorous loads, and therefore increasing PO4-P concentrations could result in increasing chlorophyll a concentrations of ponds.

Interrelationships among water quality variables.

• Chlorophyll a concentration was positively related to phosphate (PO4-P) concentrations.
• Positive relationships between fish food and sediment contributions to dominant herbivorous fish (i.e., Carassius auratus) which was bottom-feeding fish, could be attributed to accidentally consume sediment during feeding on fish food settling on the pond bottom.

Relationships between water quality & contribution of food sources to dominant herbivorous fish.

• Contribution of fish food and sediment to fish were positively related to phosphate and chlorophyll a concentrations.

Question simplification

➞ Contributions of fish food to the diet of herbivorous fish increased with PO4-P concentrations in the N-ponds.

Previous study found only 10–30% of phosphorous in commercial fish food consumed by fish is retained in fish, and the remainder of phosphorous could enter aquatic environment through excretion and feces (Boyd et al. 2002), resulting in the increase of phosphorous loads in water (Kibria et al. 1997). Therefore, fish food contributions to the diet of dominant herbivorous fish were positively related to phosphorous loads.

References

• Boyd, C.E., Wood, C., Thunjai, T., 2002. Aquaculture pond bottom soil quality management. Pond Dynamics/ Aquaculture Collaborative Research Support Program, Oregon State University, Corvallis, OR, USA.
• Kibria, G., Nugegoda, D., Fairclough, R., Lam, P., 1997. The nutrient content and the release of nutrients from fish food and faeces. Hydrobiologia 357, 165–171.