Ethology and nutrition of marbled crayfish

The marbled crayfish  (Procambarus virginalis), a unique parthenogenetic and  all-female species, has   emerged as  a  promising model  organism  in  biological research  due   to its genetic uniformity, rapid  reproduction, and  adaptability to laboratory conditions. Despite its growing use  in experimental studies, many  aspects of  its  behavior and  nutritional biology remain poorly  understood. This thesis aims  to bridge some of these gaps by examining how reproductive status  influences behavior and  feeding activity  of  females and  exploring the species’ distinct  nutritional requirements.  Combining ethological insights with  nutritional requirements deepens  our   understanding of  this   emerging  model  organism’s behavioral dynamics and species-specific dietary requirements. In Chapter 2, we aimed to investigate the daily activity  patterns of marbled crayfish   across three reproductive stages: non-reproductive (NR),  with  glair  glands (GG),  and  egg-carrying (EG) under three  experimental conditions, including i) an empty arena, ii) in an arena with  the shelter present, and  iii) in an arena with the presence of both shelter and  food. Besides well-known behavioral differences between NR and  EG females, our results provide the first comprehensive behavioral assessment of GG females which  behave differently from  both former groups. These  findings underscore  the importance of  accounting for  reproductive status in ethological research in greater detail. Additionally, the study highlights the role  of experimental timing in behavioral assessments as the activity  patterns fluctuate during the day, which should be considered when comparing results between different studies. The insights gained offer valuable contributions to crayfish behavioral  ecology and   may  apply  to other crayfish   species in  laboratory and   ecological contexts. In Chapter 3, we  further assessed the feeding activity  of marbled crayfish  across three reproductive stages (NR, GG, and  EG) under two  conditions: i) in an  empty arena and ii) in an  arena with  and  without shelter present. Using  a functional response approach, the research revealed that reproductive status of females significantly influences foraging behavior. Non-reproductive females displayed the highest feeding rates, especially when shelter was available, while egg-carrying females showed the lowest feeding activity.  Glair gland  females exhibited  intermediate   feeding  levels,   indicating  hormonally  mediated  behavioral and physiological shifts during the  reproductive cycle.  These  findings highlight the  behavioral plasticity of  marbled crayfish   and  emphasize the importance of  considering reproductive status also  when the feeding activity  is considered between female crayfish’  reproductive stages. In Chapter 4, the study aimed to define and  compare the whole-body protein of wild- caught and  laboratory-reared marbled crayfish  to identify amino acid.  Results revealed that marbled crayfish   possess a  uniquely high  leucine content,  suggesting distinct nutritional requirements compared to other crayfish  and  crustacean species. These findings highlight the potential of whole-body crayfish  protein as a rich leucine source and  underscore the necessity of  formulating species-specific diets that  reflect the unique amino acid  needs of  marbled crayfish.  In Chapters  5  and  6,  we  aimed to evaluate the optimal nutritional requirements of marbled crayfish  and  provide a foundation for  developing a SRD by examining the roles of  protein, amino acids,   energy, and   lipids.  Results highlight the  importance of  arginine and  leucine as  indispensable amino acids,  with  lysine  and  methionine as  critical  secondary components. Commercial carnivorous fish larval diets closely mirrored the amino acid profile of wild-caught individuals, suggesting its potential as a model for SRD formulation. Lipid analysis further revealed that both fatty acid  composition and  balance, particularly the ratio of high to low bioactive prostaglandin precursors balance (arachidonic acid to eicosapentaenoic acid) and  docosahexaenoic acid  content play  vital  roles  in supporting reproductive maturation, behavior, and  survival. Additionally, marbled crayfish  showed the capacity to selectively utilize
certain fatty acids  while conserving or endogenously fortifying other reproductively important fatty acid,  hinting yet unexplored fatty acid  biosynthesis pathways in this  species. Together, these  findings offer  essential guidance for  formulating a  nutritionally balanced SRD that meets the specific  physiological needs of marbled crayfish,  with  significant implications for laboratory research and  maintaining a common nutritional-physiological baseline of studied animals across laboratories worldwide.

I gratefully acknowledge financial  support from  the following  projects:
•   Ministry of Education, Youth and  Sports of the Czech Republic  – project “CENAKVA” (No.
LM2023038)
•   South Bohemian Research Centre of  Aquaculture and   Biodiversity  of  Hydrocenoses (CENAKVA, ID 90238), in accordance with  the objectives of the European consortium DANUBIUS-RI
•   Grant  Agency of the University  of South Bohemia (GAJU 059/2023/Z, GAJU 027/2022/Z)