The digestible nutrient and energy values of diets across seven marine aquaculture species demonstrate the potential and limitations for cross utility of digestibility data

The objective of this study was to examine the correlations of digestibility among seven aquaculture species when fed a suite of different diets. Using a factorial experimental design of diet and species, the digestibility of dry matter, protein, lipid, starch, and energy of fifteen different diets were assessed in each of seven tropical and temperate fish species (Asian seabass, Lates calcarifer; European seabass, Dicentrarchus labrax; European seabream, Sparus aurata; Sobaity seabream, Sparidentex hasta; Meagre, Argyrosomus regius; Pompano, Trachuris blochii; Marine tilapia, Oreochromis spiluris). The same batches of the diets were used in each experiment to minimise intradiet variability. The fish were fed each diet for one week prior to faeces being collected from each species using the same approach, where each fish was stripped of faeces under sedation. Faeces and diets were then analysed for yttrium, dry matter, protein (nitrogen), lipid, starch, and energy content to allow the determination of the digestibilities of each parameter. Significant variation was seen among diets within all species, and between species. Using a hierarchical cluster analysis of the correlations between digestibility values among species, it was evident that among the seven species that correlations in the digestibility values of the various nutritional parameters were stronger among some species than others. The greatest level of separation among species was seen within the starch and energy digestibilities of the diets. Notably, both marine tilapia and pompano tended to dichotomise differently from the other species in terms of the hierarchical cluster analysis. Trophic level was identified as a factor in the strength of those correlations, though other aspects of physiology, such as environmental preference, also align with those responses. The results support the notion that within a defined trophic level the determination of digestibility in a single indicator species may have considerable utility in predicting digestibility in other species, but that there are other factors present which necessitate a prior assessment before any application of cross-species data is applied.