Determining an effective density regime for rearing juvenile Austropotamobius pallipes in a small‐scale closed system hatchery

With recent advances in aquaculture techniques, captive‐breeding of the endangered white‐clawed crayfish Austropotamobius pallipes for restocking is becoming a widespread conservation method. Establishing optimal stocking densities for aquaculture is essential in maximizing productivity, and increases the likelihood of crayfish survival when released. A 240‐day experiment took place using 2‐month‐old juvenile, captive‐born, A. pallipes, within a small‐scale, closed‐circuit hatchery to investigate survival, growth and aggression at three treatment densities, low (100/m²), medium (200/m²) and high (300/m²). Crayfish were counted and measured every 60 days between August 2015 and April 2016. Mean survival rates were high across all three densities (87.7% ± 2.8%). Carapace length was significantly longer at low density than at medium and high densities. While growth rate was not significantly different between treatments, it was significantly higher in the first 2 months, across all three treatments (47.1% ± 6.6%) than in subsequent periods (14.1% ± 5.8%). Size variation within groups increased with density, suggesting that social dominance hierarchies are established with increasing stocking density: dominant individuals are larger and competitively exclude smaller individuals from food resources. Males were significantly larger than females from 6 months of age, (when they could be reliably sexed), in all three treatments. The larger male size suggests that sexual dimorphism begins prior to sexual maturity, with males growing faster and being more dominant and aggressive than females. In conclusion, young‐of‐the‐year A. pallipes can be reared at high densities without compromising survival; however, the optimal stocking density that maximizes growth and health is 100/m².     

Male‐biased sex ratio of nonanadromous Oncorhynchus mykiss in a partially migratory population in California

Abstract – Differential rates of anadromy between males and females are common in partially migratory salmonid populations, but this pattern is not fully clear for Oncorhynchus mykiss (rainbow trout/steelhead) from the limited but mixed data available. In particular, there are very few data on sex ratios of juvenile and nonanadromous (resident) fish to help assess sex composition of various life stages and life‐history types. We used a recently developed Y‐chromosome genetic marker to assess sex ratio of stream‐dwelling (i.e., juvenile and nonanadromous) O. mykiss in a small coastal basin in central California, USA. We analysed 384 samples collected from three contiguous study reaches over 3 years. Sex ratio was 1:1 among juvenile‐sized O. mykiss (<150 mm) but highly male‐skewed (83%) among nonanadromous‐sized individuals (≥150 mm), and this sex ratio × size pattern did not differ among years or study reaches. Our results suggest that the rate of anadromy differs between males and females in this basin. Our study also demonstrates the application of new genetic markers to determine sex composition of immature and nonanadromous salmonids, which will help assess sex‐specific life‐history behaviour in partially migratory populations of O. mykiss and other species.     

Sex‐biased survivorship and differences in migration of wild steelhead (Oncorhynchus mykiss) smolts from two coastal Oregon rivers

In salmonids with partial migration, females are more likely than males to undergo smoltification and migrate to the ocean (vs. maturing in freshwater). However, it is not known whether sex affects survivorship during smolt migration (from fresh water to entry into the ocean). We captured wild steelhead (Oncorhynchus mykiss) smolts in two coastal Oregon rivers (USA) and collected fin tissue samples for genetic sex determination (2009; N = 70 in the Alsea and N = 69 in the Nehalem, 2010; N = 25 in the Alsea). We implanted acoustic tags and monitored downstream migration and survival until entry in to the Pacific Ocean. Survival was defined as detection at an estuary/ocean transition array. We found no effect of sex on smolt survivorship in the Nehalem River in 2009, or in the Alsea River in 2010. However, males exhibited significantly lower survival than females in the Alsea River during 2009. Residency did not influence this result as an equal proportion of males and females did not reach the estuary entrance (11% of males, 9% of females). The sexes did not differ in timing or duration of migration, so those variables seem unlikely to explain sex‐biased survivorship. Larger males had higher odds of survival than smaller males in 2009, but the body size of females did not affect survivorship. The difference in survivorship between years in the Alsea River could be due to flow conditions, which were higher in 2010 than in 2009. Our findings suggest that sex may affect steelhead smolt survival during migration, but that the difference in survivorship may be weak and not a strong factor influencing adult sex ratios.     

The use of Chara spp. (Charales: Characeae) as a bioindicator of physico‐chemical habitat suitability for an endangered crayfish Austropotamobius pallipes in lentic waters

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Allometric growth patterns and development in larvae and juveniles of thick‐lipped grey mullet Chelon labrosus reared in mesocosm conditions

Allometric growth and ontogeny were studied in thick‐lipped grey mullet Chelon labrosus reared in mesocosms from 1 to 71 day post hatching (dph). Multivariate allometric analysis of morphometric growth distinguished three distinct developmental stanzas separated by two morphometric metamorphosis lengths (L_m1 = 4.46 ± 0.06 mm; L_m2 = 28.56 ± 1.04 mm). Body mass growth also showed three distinct episodes separated by two inflections, correlated with morpho‐functional changes. First episode concerned pre‐flexion larvae and ended around 4.5 mm‐L_T (14‐dph), coinciding with estimated L_m1. It was distinguished by reduced growth, but intense morphogenesis and differentiation processes. Organogenesis and allometric changes indicated that development priorities concerned feeding efficiency, by improving detection ability (sensory system development), ingestion capacity (head growth) and assimilation performance (digestive system differentiation), together with respiration efficiency (gill development). Second episode concerned post‐flexion larvae and, ended around 8.6 mm‐L_T (25‐dph). It was distinguished by fast growth of trunk and tail, acquisition of adult axial muscle distribution and completion of gill filament development, improving locomotion and oxygenation performances. It corresponded to transition towards metamorphosing stage as indicated by later isometric growth, musculature maturation and acquisition of juvenile phenotype. Metamorphosis seemed to end at L_m2, suggesting to avoid zootechnic handling before this size.     

The role of gape‐limitation in intraguild predation between endangered Mohave tui chub and non‐native western mosquitofish

Intraguild predation (IGP) is a mechanism that may facilitate the co‐existence of native species with non‐native invasive species. We conducted laboratory predation trials to assess the role of predator gape‐limitation in the context of IGP between the endangered Mohave tui chub (Siphateles bicolor mohavensis) and invasive western mosquitofish (Gambusia affinis). Larval tui chubs had significantly lower (χ² = 74.74; P < 0.001) survival in the presence of female mosquitofish (10.0%) than in the presence of male mosquitofish (73.3%). Reciprocally, adult tui chubs preyed upon adult mosquitofish, causing a significantly lower (χ² = 11.33; P < 0.001) survival for male mosquitofish (60%) compared to female mosquitofish survival (96.7%). Vulnerability modelling revealed that mosquitofish with a body depth < 4.6 mm and a larval tui chub with a body depth < 1.2 mm were completely vulnerable to predation by adult Mohave tui chub and adult mosquitofish, respectively. IGP in this study system is size‐structured based on gape‐size limitation and may have some conservation implications for the recovery of endangered Mohave tui chub. Our findings also provide an important caveat to the dogmatic view of mosquitofish as a threat whenever they invade. It is important to note that many previous studies that reported negative impacts of mosquitofish involved native species with relatively small body sizes, often the same size as mosquitofish.     

A preliminary study on the use of mannan oligosaccharides (MOS) in freshwater crayfish, <Emphasis Type="Italic">Astacus leptodactylus</Emphasis> Eschscholtz, 1823 juvenile diets

The effects of dietary mannan oligosaccharides (MOS) on the survival and growth of Astacus leptodactylus juveniles were evaluated. Experimental diets were prepared by using supplementation of 0 (Control), 1.5, 3.0, and 4.5 g MOS kg⁻¹ commercial trout larvae diet containing 43 g kg⁻¹ protein and 15.74 g kg⁻¹ lipid. A. leptodactylus juvenile with an average total length of 3.6 ± 0.46 cm (TL) and average weight of 1.25 ± 0.43 g was stocked in 0.2-m² aquariums at a rate of 50 crayfish/m² and reared for 60 days at 22.8°C. The experiment consisted of four treatments with three replicates each. Each aquarium contained ten crayfish. Crayfish juvenile fed with 0, 1.5, 3.0, and 4.5 MOS attained 6.15 ± 0.49, 5.94 ± 0.29, 7.34 ± 0.39, and 5.94 ± 0.27 cm final total length and 50, 56.67, 46.67, and 50% survival rates, respectively. Moreover, molting frequencies in 0, 1.5, 3.0, and 4.5 g kg⁻¹ MOS groups were detected as 44.44, 61.11, 83.33, and 38.88%, respectively. At the end of the experiment, a general enhanced growth performance (P < 0.05) and feed conversion ratio were observed in crayfish fed on the diet containing 3.0 g kg⁻¹. Crayfish juveniles fed with 3.0 g kg⁻¹ MOS had the highest final length (7.34 ± 0.39 cm), although their survival was the lowest (46.67%) compared to other treatments but not significant. Specific growth rates were significantly different (P < 0.05) among the treatment groups at the end of the 60-day experiment. There were no significant differences (P > 0.05) in percentage moisture, protein, and ash (wet-weight basis) in the tail meat of A. leptodactylus juvenile among treatments (diet) that averaged 82.3, 16.1, and 1.2%, respectively. However, lipid value was significantly different among the diets P < 0.05), with values between 0.13 and 0.32. From the current results, it could be advised to use MOS at the rate of 3.0 g kg⁻¹ in A. leptodactylus juvenile diets.     

Effect of dietary encapsulated organic salts (Na‐acetate,Na‐butyrate,Na‐lactate and Na‐propionate) on growth performance,haemolymph, antioxidant and digestive enzyme activities and gut microbiota of juvenile narrow clawed crayfish,Astacus leptodactylus leptodactylus Eschscholtz, 1823

A 63‐day experiment was done to study the effects of four levels (5, 10, 20 and 50 g/kg) of encapsulated organic salts (Na‐acetate, Na‐butyrate, Na‐lactate and Na‐propionate) on the growth indices and haemato‐immunological responses of crayfish Astacus leptodactylus leptodactylus (4.38 ± 0.08 g). Crayfish were distributed at 51 1,000‐L tanks (17 treatments at triplicate). The highest values of final weight (27.86 g), specific growth rate (2.94% body weight per day) and survival rate (96%) were observed in the crayfish fed the 20 g/kg of encapsulated Na‐propionate diet (p < .05). The highest activities of phenoloxidase (7.4 U/min), superoxide dismutase (7.80 U/min) and lysozyme (9.40 U/min) were observed in the gut of crayfish fed the 20 g/kg of encapsulated Na‐propionate diet (p < .05), as well as the highest activities of alkaline protease (10.70 U/mg), lipase (9.10 U/mg), amylase (9.60 U/mg) and the lactobacillus count (p < .05). Broken line regression model of SGR and phenoloxidase activity suggested that the optimum dietary levels of encapsulated Na‐acetate, Na‐butyrate, Na‐lactate and Na‐propionate could be 30.7, 31.8, 31.4 and 33.5 g/kg, respectively, in crayfish reared in culture conditions.     

Effects of estradiol‐17β on survival,growth performance,gonadal structure and sex ratio of the tiger puffer,Takifugu rubripes (Temminck & Schlegel, 1850), fingerlings

Systematic research was performed to assess the survival, growth performance, gonadal structure and sex ratio during and after sex reversal induced by estradiol‐17β in tiger puffers. The fish of 20 days after hatching (dah) were immersed in different doses (0.2, 2, 20, 100 ppb) for 60 days. There were significant differences in survival rates among groups (p < .05). With the increase in the estradiol‐17β dose, the survival rates of tiger puffers decreased, revealing a linear regression relationship with log₁₀ (estradiol + 1; p < .05). The growth tendency of fish in the low‐dose group was similar to those in the control group over the same period. The growth in the 20 ppb dose group was significantly slower than in the low‐dose and control groups in fish of same age (p < .05), but was significantly faster than in the 100 ppb dose group (p < .05) after 60 days. Intersex fish were categorized into intersex I, II and III types, according to the feminization degree from low to high. Phenotypic intersex puffer fish were found in the 2, 20 and 100 ppb dose groups. Intersex ratios in 2, 20 and 100 ppb were 10%, 43.3% and 46.7%, respectively, the ratios except the ones in 2 ppb group being significantly higher than those in the control group (p < .05). Moreover, 100.0% male induction for intersex II and III types occurred in 20 and 100 ppb groups. Together, these results indicated that estradiol‐17β at a dose of 20 ppb was most effective for pseudo‐female production.     

Baseline demographics of a non‐native lake trout population and inferences for suppression from sensitivity‐elasticity analyses

Management agencies in several western states of the United States are implementing suppression programmes to control non‐native lake trout, Salvelinus namaycush (Walbaum), for the conservation of native species. This study was implemented to ascertain the population demographics of an expanding lake trout population and use those data to construct an age‐structured model to inform suppression efforts. Population projection matrices were used to model population growth and identify age or stage classes with the greatest influence on population growth. The size and age structure of lake trout sampled was skewed towards juveniles, indicating strong recruitment and a growing population. Matrix‐model simulations corroborated the observed size and age structure, as the lake trout population was predicted to grow exponentially (λ = 1.35, 95% CL: 1.25–1.43) with no suppression efforts. Elasticity analysis of matrix models indicated the relative contribution of survival rates to population growth among immature age classes was equal from age 0 to age at first maturity, but immature survival rates contributed more than adult survival and fertility rates. These results emphasise the importance of targeting juvenile lake trout for suppression efforts during exponential growth in recently established populations.     

Effects of vitamin C inclusion in practical diets on survival and growth of juvenile crayfish (Pacifastacus leniusculus Dana,Astacidae) from the onset of exogenous feeding

The aim of this study was to evaluate the effects of practical diets with different levels of vitamin C on survival and growth of juvenile crayfish (Pacifastacus leniusculus). An 80‐day trial was conducted with stage 2 juveniles from the onset of exogenous feeding. Four practical diets differing in the content of l ‐ascorbyl‐2‐monophosphate‐Na were prepared: 0, 0.2, 0.4 or 0.8 g kg^?1 diet. Each diet was tested on grouped or individually isolated crayfish. Diets had no significant effects on survival of crayfish held in groups (average: 73.1%) neither on the isolated ones (average: 90%). Crayfish fed the diet with 0.2 g kg^?1 of l ‐ascorbyl‐2‐monophosphate‐Na had the highest growth (groups: 13.64 mm carapace length (CL), 542.4 mg weight; isolated: 17.05 mm CL, 1213.2 mg weight) and the lowest feed conversion ratio (average of grouped and isolated: 0.99). This study provides the first data on vitamin C requirements of freshwater crayfish. A level of 0.2 g l ‐ascorbyl‐2‐monophosphate‐Na kg^?1 diet (0.07 g ascorbic acid equivalent) can be recommended for juvenile P. leniusculus during the first period of intensive rearing.     

Effects of dietary L‐lysine supplementation on growth,body composition and muscle‐growth‐related gene expression with an estimation of lysine requirement of GIFT tilapia

An 8‐week feeding trial was conducted with extruded practical diets containing 320 g/kg of crude protein from plant‐based sources to determine the effects of L‐lysine on growth performances, muscle‐growth‐related gene (myoD, myogenine and myostatin) expression and haemato‐biochemical responses in juvenile genetically improved farmed tilapia (GIFT). Five isonitrogenous and isoenergetic diets were formulated to contain graded levels of lysine (14.3, 16, 17.5, 19 and 20.5 g/kg of diet). Each diet was randomly assigned to triplicate groups of 30 juvenile fish (5.2 ± 0.1 g), which were fed thrice a day (9:00, 13:00 and 17:00 hr). Maximum growth performances were observed in fish fed with lysine at 19 g/kg of diet. There was no significant (p > .05) effect on whole‐body composition and amino acids profile by dietary lysine supplementation. Significant (p < .05) changes were observed in relative expression of muscle‐growth‐related genes namely myoD and myogenine and in plasma metabolites by dietary lysine supplementation. In contrast, the relative expression of myostatin was not affected by dietary lysine supplementation. Broken‐line regression analysis and second‐order polynomial regression analysis of weight gain and N gain against dietary lysine levels showed that the dietary lysine requirement for juvenile GIFT tilapia was 18–18.3 g/kg of diet and 19.3–19.5 g/kg of diet, respectively.     

Effect of photoperiod and tank colour on growth and survival of pelagic‐phase seahorse Hippocampus reidi

The effect of photoperiod and tank colour on the survival and growth of juvenile seahorse Hippocampus reidi was investigated in the first 15 days after release (DAR). In the first experiment, newly released seahorses were exposed to six photoperiods – 6 h of light (L):18 h of darkness (D), 10L:14D, 12L:12D, 14L:10D, 18L:6D and 24L:0D. In the second experiment, juveniles were kept in tanks of different background colours – blue, white, black, clear and red. No significant differences were observed in the growth and survival among seahorse subjected to 10–24 h of light (P > 0.05). At the end of 15 DAR, fish exposed to 6L:18D showed lower growth in height and weight compared to other treatments (13.8 mm vs. 20.0–22.2 mm and 13.4 mg vs. 37.2–43.2 mg respectively) and lower survival (80% vs. 88–95% respectively). Tank colour did not affect growth and survival of juveniles up to 15 DAR.     

The effect of dietary n‐3 series fatty acids on the number of pleopadal egg and stage 1 juvenile in freshwater crayfish,Astacus leptodactylus Eschscholtz

The effect of dietary n‐3 series fatty acids on the number of pleopadal egg and stage 1 juvenile in freshwater crayfish, Astacus leptodactylus was investigated. Crayfish were fed with n‐3 series fatty acids supplemented diets and a control diet for 251 days. Control diet did not comprise additional n‐3 series fatty acids. However, D2, D3 and D4 groups were supplemented with n‐3 series fatty acids at 1%, 2% and 3% level respectively. Results showed the beneficial effects of dietary n‐3 series fatty acids on the production of pleopodal egg and stage 1 juvenile number. At the end of the experiment, pleopodal egg (from 177 to 234) and stage 1 juvenile number (from 167 to 225) increased significantly with increased dietary n‐3 series fatty acid level. In addition, an increase in dietary n‐3 series fatty acids led to an increase in number of pleopodal egg and stage 1 juvenile produced per gram of female crayfish weight. It can be concluded that the reproductive efficiency of A. leptodactylus (i.e., pleopodal egg and stage 1 juvenile number) can be improved in controlled hatchery conditions by adding n‐3 series fatty acid into the diet of this species.     

Identification of growth‐related nucleotide polymorphism in cultured Pacific bluefin tuna,Thunnus orientalis

Pacific bluefin tuna (PBF), Thunnus orientalis, is commercially one of the most important species of tuna. In this study, amplified fragment length polymorphism (AFLP) screening was conducted to find the growth‐related polymorphic DNA in cultured PBF. Fish hatched in 2007 were harvested at an age of 818–1994 days. They were categorized into superior, average and inferior growth groups, depending on their growth score at the time of harvest. On AFLP screening of 24 fish, with eight fish from each group, 215 polymorphic DNA fragments were observed. A second amplification, with EcoRI + ACC and MseI + CCC primers, generated a polymorphic fragment of 630 bp at a rate of 80.0% (n = 15) in the superior, 56.3% (n = 16) in the average and 20.0% (n = 15) in the inferior growth groups. Polymerase chain reaction (PCR) primers, which could amplify both AFLP‐positive and AFLP‐negative loci, were developed using the consensus sequence outside the AFLP target fragment. Eleven haplotypes were obtained by sequence analysis of the PCR product at the AFLP target loci. Among those, haplotype 1 was statistically significant in the superior and average growth groups and could be used as a molecular marker for distinguishing the individuals with superior and average growth from those with inferior growth.     

Effects of co‐supply ratios of swimming crab Portunus trituberculatus zoeae and Artemia on survival and growth of East Asian common octopus Octopus sinensis paralarvae under an upwelling culture system

Despite recent advances in culture technology for East Asian common octopus Octopus sinensis paralarvae using upwelling systems, securing suitable feed for the paralarvae is an unresolved issue. The zoea of the swimming crab Portunus trituberculatus is a good candidate for paralarval feed because of the high fecundity of the adult females. To investigate the effects of supplying P. trituberculatus zoeae and their feeding method on paralarvae, we cultured paralarvae with supplying different combination ratios of zoeae and Artemia (10:0, 7:3, 5:5, 3:7 and 0:10), and with or without supplementing rotifers using small‐scale (3‐L) upwelling systems. Paralarval survival rate and growth were improved when zoeae were supplied as the main feed, but reduced when the proportion of Artemia exceeded half the whole preys. Supplementing rotifers did not affect the paralarval survival and growth. Subsequently, paralarvae were cultured by supplying zoeae (partially augmented by Artemia) using three large (1‐kl) upwelling systems to assess their feeding effectiveness in juvenile octopus production. Paralarvae could be cultured at high survival rates of 77.1 ± 5.1% to reach benthic juveniles at 23 days after hatching. In conclusion, supplying P. trituberculatus zoeae augmented with Artemia under an upwelling culture system has great potential for juvenile octopus production.     

Impacts of parasites on marine survival of Atlantic salmon: a meta‐analysis

Parasites can, in theory, have large impacts on the survival of fish populations. One method to evaluate such impacts on anadromous species is to apply manipulative field experiments in which parallel groups of antiparasitically treated and non‐treated fish are simultaneously released and then subsequently recaptured as returning adults. A systematic review and meta‐analysis on all such Norwegian studies on Salmo salar provided a data set for the time period 1996 to 2011 on 118 release groups comprising 657 624 fish released and 3989 recaptured. The overall risk ratio (RR) was estimated to be 1.18 (95% CI: 1.07–1.30). The effect varied strongly between groups, (Higgins I² = 40.1%). Over 70% of this heterogeneity could be explained by the release location, time period and baseline survival. The most important predictor variable was baseline survival. In groups with low recapture in the control group (low baseline survival), the effect of treatment was high (RR = 1.7), while in groups with high recapture in the control group (high baseline survival), there was no effect of treatment (RR ~ 1.00). The most prevalent parasite in the region affected by the drugs administered was Lepeophtheirus salmonis. Hence, the meta‐analysis supports the hypothesis that L. salmonis contributes to the mortality of S. salar during outward migration. However, the effect of treatment was not consistent, but was evidently strongly modulated by other risk factors. The results suggest that the population‐level effects of parasites cannot be estimated independently of other factors affecting the marine survival of S. salar.     

Influence of oceanographic conditions on abundance and distribution of post‐larval and juvenile carangid fishes in the northern Gulf of Mexico

Relationships between abundance of post‐larval and juvenile carangid (jacks) fishes and physical oceanographic conditions were examined in the northern Gulf of Mexico (GoM) in 2011 with high freshwater input from the Mississippi River. Generalized additive models (GAMs) were used to explore complex relationships between carangid abundance and physical oceanographic data of sea surface temperature (SST), sea surface height anomaly (SSHA) and salinity. The five most abundant carangid species collected were: Selene setapinnis (34%); Caranx crysos (30%); Caranx hippos (10%); Chloroscombrus chrysurus (9%) and Trachurus lathami (8%). Post‐larval carangids (median standard length [SL] = 10 mm) were less abundant during the spring and early summer, but more abundant during the late summer and fall, suggesting summer to fall spawning for most species. Juvenile carangid (median SL = 23 mm) abundance also increased between the mid‐summer and early fall. Most species showed increased abundance at lower salinities and higher temperatures, suggesting entrainment of post‐larval fishes or feeding aggregations of juveniles at frontal convergence zones between the expansive river plume and dynamic mesoscale eddy water masses. However, responses were species‐ and life‐stage specific, which may indicate fine‐scale habitat partitioning between species. Ordination methods also revealed higher carangid abundances at lower salinities for both post‐larval and juvenile life stages, with species‐ and life‐stage specific responses to SST and SSHA, further suggesting habitat separation between species. Results indicate strong links between physical oceanographic features and carangid distributions in the dynamic northern GoM.     

Growth,sex ratio,and maturation rate with age in the blackspot tuskfish <Emphasis Type="Italic">Choerodon schoenleinii</Emphasis> in waters off Okinawa Island,southwestern Japan

The growth, sex ratio with age, and age at sexual maturation were determined based on sectioned otoliths in 257 specimens of the blackspot tuskfish Choerodon schoenleinii collected in waters off Ryukyu Island. Opaque rings observed by reflected light in the sectioned otoliths were found to form once a year from January to July. The three growth parameters of the von Bertalanffy growth equation were L_∞ = 68.1 (cm), k = 0.263, and t ₀ = −0.023 (year). The age at which the sex ratio reached 50% by sexual transition was about 6.15 years, and the age at which 50% of females were sexually mature was approximately 2 years. The oldest specimen among the samples was 17 years old.     

Development of release methods for captive‐bred freshwater pearl mussels (Margaritifera margaritifera

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