Genetic diversity in three redclaw crayfish (Cherax quadricarinatus, von Martens) lines developed in culture in China

The redclaw crayfish Cherax quadricarinatus (von Martens) accounts for the entire commercial production of freshwater crayfish in Australia. Two forms have been recognized, an 'Eastern' form in northern Queensland and a 'Western' form in the Northern Territory and far northern Western Australia. To date, only the Eastern form has been exported overseas for culture (including to China). The genetic structure of three Chinese redclaw crayfish culture lines from three different geographical locations in China (Xiamen in Fujian Province, Guangzhou in Guangdong Province and Chongming in Shanghai) were investigated for their levels and patterns of genetic diversity using microsatellite markers. Twenty-eight SSR markers were isolated and used to analyse genetic diversity levels in three redclaw crayfish culture lines in China. This study set out to improve the current understanding of the molecular genetic characteristics of imported strains of redclaw crayfish reared in China. Microsatellite analysis revealed moderate allelic and high gene diversity in all three culture lines. Polymorphism information content estimates for polymorphic loci varied between 0.1168 and 0.8040, while pairwise F ST values among culture lines were moderate (0.0020-0.1244). The highest estimate of divergence was evident between the Xiamen and Guangzhou populations.

Effects of soluble dietary cellulose on specific growth rate, survival and digestive enzyme activities in three freshwater crayfish (Cherax) species

Three native freshwater crayfish Cherax species are farmed in Australia namely; Redclaw (Cherax quadricarinatus), Marron (C. tenuimanus), and Yabby (C. destructor). Lack of appropriate data on specific nutrient requirements for each of these species, however, has constrained development of specific formulated diets and hence current use of over-formulated feeds or expensive marine shrimp feeds, limit their profitability. A number of studies have investigated nutritional requirements in redclaw that have focused on replacing expensive fish meal in formulated feeds with non-protein, less expensive substitutes including plant based ingredients. Confirmation that freshwater crayfish possess endogenous cellulase genes, suggests their potential ability to utilize complex carbohydrates like cellulose as nutrient sources in their diet. To date, studies have been limited to only C. quadricarinatus and C. destructor and no studies have compared the relative ability of each species to utilize soluble cellulose in their diets. Individual feeding trials of late-juveniles of each species were conducted separately in an automated recirculating culture system over 12 week cycles. Animals were fed either a test diet (TD) that contained 20% soluble cellulose or a reference diet (RD) substituted with the same amount of corn starch. Water temperature, conductivity and pH were maintained at constant and optimum levels for each species. Animals were fed at 3% of their body weight twice daily and wet body weight was recorded bi-weekly. At the end of experiment, all animals were harvested, measured and midgut gland extracts assayed for alpha-amylase, total protease and cellulase activity levels. After the trial period, redclaw fed with RD showed significantly higher (p<0.05) specific growth rate (SGR) compare with animals fed the TD while SGR of marron and yabby fed the two diets were not significantly different (p<0.05). Cellulase expression levels in redclaw were not significantly different between diets. Marron and yabby showed significantly higher cellulase activity when fed the RD. Amylase and protease activity in all three species were significantly higher in the animals fed with RD (Table 1). These results indicate that test animals of all species can utilize starch better than dietary soluble cellulose in their diet and inclusion of 20% soluble cellulose in diets does not appear to have any significant negative effect on their growth rate but survival was impacted in C. quadricarinatus while not in C. tenuimanus or C. destructor.

Effects of soluble dietary cellulose on specific growth rate, survival and digestive enzyme activities in three freshwater crayfish (Cherax) species

The current study evaluated the effect of soluble dietary cellulose on growth, survival and digestive enzyme activity in three endemic, Australian freshwater crayfish species (redclaw: Cherax quadricarinatus, marron: C. tenuimanus, yabby: C. destructor). Separate individual feeding trials were conducted for late-stage juveniles from each species in an automated recirculating freshwater, culture system. Animals were fed either a test diet (TD) that contained 20% soluble cellulose or a reference diet (RD) substituted with the same amount of corn starch, over a 12 week period. Redclaw fed with RD showed significantly higher (p<0.05) specific growth rates (SGR) compared with animals fed the TD, while SGR of marron and yabby fed the two diets were not significantly different. Expressed cellulase activity levels in redclaw were not significantly different between diets. Marron and yabby showed significantly higher cellulase activity when fed the RD (p<0.05). Amylase and protease activity in all three species were significantly higher in the animals fed with RD (p<0.05). These results indicate that test animals of all three species appear to utilize starch more efficiently than soluble dietary cellulose in their diet. The inclusion of 20% soluble cellulose in diets did not appear, however, to have a significant negative effect on growth rates.

An investigation of functional diversity of endogenous cellulase and expression of other digestive enzyme genes in freshwater crayfish (Cherax) species

The project evaluated potential of soluble cellulose as a cheap feed ingredient for major farmed Australian freshwater crayfish species testing their growth performance, digestive enzyme activity and digestive enzyme gene expression patterns. Test animals showed an innate capacity to utilise a range of carbohydrate sources including complex structural polysaccharides. Results suggest that more plant-derived ingredient can be incorporated in formulated low-cost feeds for the culture industry.

Expression and characterization of digestive enzyme genes from hepatopancreatic transcripts from redclaw crayfish (Cherax quadricarinatus)

Redclaw crayfish, Cherax quadricarinatus, possess a number of biological and commercial attributes that make them ideal for commercial aquaculture. While some studies have investigated digestive enzyme activity and nutritional requirements of this species, little information exists about the expression of digestive enzyme genes and their role in regulating digestive capacity. The current study therefore sequenced and annotated a RNASeq library constructed from a redclaw hepatopancreas to identify genes involved in digestive enzyme production. We observed that most of the transcripts that were annotated as digestive enzyme genes are associated with carbohydrate metabolism, thus confirming that redclaw have an innate capacity to digest a range of carbohydrate substrates. While endoglucanases were the most abundant group of digestive enzymes found, a number of novel transcripts were also detected. Here, we provide the first report for the presence and expression of endo-b-mannanase in freshwater crayfish. This novel gene showed significant alignment with a GH5 family protein from marine Limnoriids, wood borers that do not possess symbiotic microbes in their gut system. Overall, the data generated here provide an important resource to better understand the suite of digestive enzymes in redclaw that are very useful to fully utilize the species’ digestive capacity and will assist development of specific artificial feeds.

Analysis, characterisation and expression of gill-expressed carbonic anhydrase genes in the freshwater crayfish Cherax quadricarinatus

Changes in water quality parameters such as pH and salinity can have a significant effect on productivity of aquaculture species. Similarly, relative osmotic pressure influences various physiological processes and regulates expression of a number of osmoregulatory genes. Among those, carbonic anhydrase (CA) plays a key role in systemic acid–base balance and ion regulation. Redclaw crayfish (Cherax quadricarinatus) are unique in their ability to thrive in environments with naturally varied pH levels, suggesting unique adaptation to pH stress. To date, however, no studies have focused on identification and characterisation of CA or other osmoregulatory genes in C. quadricarinatus. Here, we analysed the redclaw gill transcriptome and characterized CA genes along with a number of other key osmoregulatory genes that were identified in the transcriptome. We also examined patterns of gene expression of these CA genes when exposed to three pH treatments. In total, 72,382,710 paired end Illumina reads were assembled into 36,128 contigs with an average length of 800 bp. Approximately 37% of contigs received significant BLAST hits and 22% were assigned gene ontology terms. Three full length CA isoforms; cytoplasmic CA (ChqCAc), glycosyl-phosphatidylinositol-linked CA (ChqCAg), and β-CA (ChqCA-beta) as well as two partial CA gene sequences were identified. Both partial CA genes showed high similarity to ChqCAg and appeared to be duplicated from the ChqCAg. Full length coding sequences of Na+/K+-ATPase, V-type H+-ATPase, sarcoplasmic Ca+-ATPase, arginine kinase, calreticulin and Cl− channel protein 2 were also identified. Only the ChqCAc gene showed significant differences in expression across the three pH treatments. These data provide valuable information on the gill expressed CA genes and their expression patterns in freshwater crayfish. Overall our data suggest an important role for the ChqCAc gene in response to changes in pH and in systemic acid–base balance in freshwater crayfish.

Comparative analysis of gill transcriptomes of two freshwater crayfish, Cherax cainii and C. destructor

We undertook deep sequencing of gill transcriptomes from two freshwater crayfish, Cherax cainii and Cherax destructor, in order to generate genomic resources for future genomics research. Over 83 and 100 million high quality (quality score (Q) ≥ 30) paired-end Illumina reads (150 bp) were assembled into 147,101 and 136,622 contigs in C. cainii and C. destructor, respectively. A total of 24,630 and 23,623 contigs received significant BLASTx hits and allowed the identification of multiple gill expressed candidate genes associated with pH and salinity balance. These functionally annotated transcripts will provide a resource to facilitate comparative genomic research in the genus Cherax, and in particular allow insights into respiratory and osmoregulatory physiology of this group of animals.

The fishery and reproductive biology of Barking crayfish, Linuparus trigonus (Von Siebold, 1824) along Queenslands east coast

This paper describes the fishery and reproductive biology for Linuparus trigonus obtained from trawl fishermen operating off Queensland’s east coast, Australia. The smallest mature female lobster measured 59.8 mm CL, however, 50% maturity was reached between 80 and 85 mm CL. Brood fecundity (BF) was size dependent and ranged between 19,287 and 100,671 eggs in 32 females from 59.8 to 104.3 mm CL. The relationship was best described by the power equation BF = 0.1107*CL to the power of 2.9241 (r to the power of 2 = 0:74). Egg size ranged from 0.96 to 1.12 mm in diameter (mean = 1:02 (+or-) 0:01 mm). Egg weight and size were independent of lobster size. Length frequencies displayed multi-modal distributions.The percentage of female to male lobsters was relatively stable for small size classes (30 to 70 mm CL; 50.0 to 63.6% females), but female proportions rose markedly between 75 and 90 mm (72.2 to 85.4%) suggesting that at the onset of sexual maturity female growth rates are reduced. In size classes greater than 95 mm, males were numerically dominant. A description of the L. trigonus fishery in Queensland is also detailed.

Food intake, growth and social interactions of signal crayfish, Pacifastacus leniusculus (Dana)

The knowledge about the optimal rearing conditions, such as water temperature and quality, photoperiod and density, with the understanding of animal nutritional requirements forms the basis of economically stable aquaculture for freshwater crayfish. However, the shift from a natural environment to effective culture conditions induces several changes, not only at the population level, but also at the individual level. The social contacts between conspecifics increase with increasing animal density. The competition for limited resources (e.g. food, shelter, mates) is more severe with the presence of agonistic behaviour and may lead to unequal distribution of these. The objectives of this study were to: 1) study the distribution of a common food resource between communally reared signal crayfish (Pacifastacus leniusculus) and to assign potential feeding hierarchy on the basis of individual food intake measurements, 2) explore the possibilities of size distribution manipulations to affect population dynamics and food intake to improve growth and survival in culture and 3) study the effect of food ration and spatial distribution on food intake and to explore the effect of temperature and food ration on growth and body composition of freshwater crayfish. The feeding ranks between animals were assigned with a new method for individual food intake measurement of communally reared crayfish. This technique has a high feasibility and a great potential to be applied in crayfish aquaculture studies. In this study, signal crayfish showed high size-related variability in food consumption both among individuals within a group (inter-individual) and within individual day-to-day variation (intra-individual). Increased competition for food led to an unequal distribution of this resource and this may be a reason for large growth differences between animals. The consumption was significantly higher when reared individually in comparison with communal housing. These results suggest that communally housed crayfish form a feeding hierarchy and that the animal size is the major factor controlling the position in this hierarchy. The optimisation of the social environment ( social conditions ) was evaluated in this study as a new approach to crayfish aquaculture. The results showed that the absence of conspecifics (individual rearing vs. communal housing) affects growth rate, food intake and the proportion of injured animals, whereas size variation between animals influences the number and duration of agonistic encounters. In addition, animal size had a strong influence on the fighting success of signal crayfish reared in a social milieu with a wide size variation of conspecifics. Larger individuals initiated and won most of the competitions, which suggests size-based social hierarchy of P. leniusculus. This is further supported by the fact that the length and weight gain of smaller animals increased after size grading, maybe because of a better access to the food resource due to diminished social pressure. However, the high dominance index was not based on size under conditions of limited size variation, e.g. those characteristic of restocked natural populations and aquaculture, indicating the important role of behaviour on social hierarchy.

Characterization of the carbonic anhydrase gene family and other key osmoregulatory genes in Australian freshwater crayfish (genus Cherax)

Cherax quadricarinatus (Redclaw), C. destructor (Yabby) and C. cainii (Marron) are a group of economically important freshwater crayfish and have been developed for aquaculture production in many countries. As crayfish are farmed in a wide range of culture conditions, optimisation of water quality parameters, are crucial for their maximum growth performance. Previous reports have shown that fluctuations in water quality can negatively impact on growth of crayfish. Therefore, this project aims to identify and characterize the major genes that enable freshwater crayfish to persist in different water chemistries and evaluate their patterns of expression under different water parameters. Overall, this project found a number of candidate genes in all three species and determined that water chemistry had a strong influence on the expression of candidate genes. This information is important in the optimization of water quality parameters in freshwater crayfish aquaculture production.

Transcriptome analysis and characterisation of gill-expressed carbonic anhydrase and other key osmoregulatory genes in freshwater crayfish Cherax quadricarinatus

The pH and salinity balance mechanisms of crayfish are controlled by a set of transport-related genes. We identified a set of the genes from the gill transcriptome from a freshwater crayfish Cherax quadricarinatus using the Illumina NGS-sequencing technology. We identified and characterized carbonic anhydrase (CA) genes and some other key genes involved in systematic acid-base balance and osmotic/ionic regulation. We also examined expression patterns of some of these genes across different sublethal pH levels [1]. A total of 72,382,710 paired-end Illumina reads were assembled into 36,128 contigs with an average length of 800 bp. About 37% of the contigs received significant BLAST hits and 22% were assigned gene ontology terms. These data will assist in further physiological-genomic studies in crayfish.

A review of the crayfish fishery of Nigeria with special reference to the Cross River State

The fishery for crayfish is of considerable importance in the maritime region of the Cross River State, Nigeria, where it forms an important occupation of a host of fishermen. Crayfish landings from this State contributed 11% to the national marine fish landings within the period 1980 to 1984 and also in the same period the volume of crayfish alone formed 26% of the marine fish landings within the State. The species exploited as crayfish include Palaemon hastatus; Hippolysmata hastatoides, and Macrobrachium sp; mixed with the larval, and juveniles of pink shrimp Panaeus dourarum. They are generally small in size ranging from 7 cm (maximum) to 2.5 cm. Crayfish are caught all year round along the Niger Delta, but particularly along the river estuaries and littoral waters of the Cross River State with the highest production occurring in March to May. Crayfish are usually smoked, and occasionally sun-dried, and they form an indispensable food item in the diet of the people of the entire southern States in particular and Nigeria in general. It appears that crayfish landings could be substantially increased without depleting the stock, if a proper exploratory survey is undertaken of the Niger delta, and the Cross River estuaries to chart potentially rich grounds of this resource