Abstract
New and viable species for aquaponics and integrated multi‐trophic aquaculture (IMTA) in freshwater systems can improve yields and sustainability of aquaculture. Freshwater crayfish species such as Astacus astacus and Pontastacus leptodactylus are omnivorous feeders and considered candidates for feeding on faecal matters in existing aquaculture systems. Feeding trials were conducted to determine growth response and RNA/DNA ratio in freshwater crayfish fed fish waste. Carapace length and wet weight were measured to determine the growth response. Juvenile A. astacus was fed faeces of hybrid striped bass (Morone chrysops × Morone saxatilis) and rainbow trout (Oncorhynchus mykiss), while adult P. leptodactylus was fed with two commercial pellet diets and pikeperch (Sander lucioperca) faeces. The nutritional composition of hybrid striped bass faeces was close to optimal diet composition of A. astacus, and crayfish showed significantly higher carapace growth, weight gain and weight gain per moult as the group fed rainbow trout faeces. The growth of P. leptodactylus was significantly lower in terms of weight gain and weight gain percentage per moult for crayfish fed on pikeperch faeces. Thus, this study can recommend a co‐cultivation of hybrid striped bass and A. astacus within one system, but cannot recommend co‐cultivation of P. leptodactylus with pikeperch. Additionally, this study showed controversial results of RNA/DNA ratio and weight gain of both crayfish species. Thus, RNA/DNA ratio cannot be approved for investigations on crayfish physiological status in controlled feeding experiments if animals are fed with an inadequate diet.
Highlights
Increasing energy costs and limited availability of natural resources drive demand to improve aquaculture system efficiency
There are a few studies on the ribonucleic acid (RNA)/deoxyribonucleic acid (DNA) ratio relating to crayfish, and this study reveals the effect of cultivation of crayfish feeding exclusively on faeces for the first time
This study addressed two questions: whether the two crayfish species are promising candidates for integrated multi-trophic aquaculture systems (IMTA) and whether the RNA/DNA ratio can be used as an early parameter for physiological status if no suitable feed is supplied
Summary
Increasing energy costs and limited availability of natural resources drive demand to improve aquaculture system efficiency. Previous studies on crustaceans showed precise results from RNA/DNA analyses for the effect of different feeding intervals (Grimm et al, 2015; Moss, Harbor, & Loa, 1994), different algal diets (Moss, 1994) and even within different developmental stages (Moss, 1994; Moss et al, 1994; Vrede, Persson, & Aronsen, 2002) This method was included in the current study as an attempt to determine the physiological status of Astacus astacus and Pontastacus leptodactylus feeding on different commercial diets and fish faeces, respectively, with the longer-term intention to gain insight into the feasibility of rearing them in aquaponics or IMTA. RNA/DNA ratio should react more sensitively to nutritional and physiological status within crayfish and detect differences, which cannot yet be seen in growth performance
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