Captive Broodstock Research Articles

Reintroduction of spring‐run Chinook salmon in the San Joaquin River: Evaluating genetic and phenotypic effects of captive breeding

AbstractCaptive‐breeding programs are increasingly implemented to curb population declines but can have unintended negative effects on genetic diversity and phenotypes. Through an analysis of ~10 years of genetic monitoring, pedigree information, and phenotypic data, we evaluated a captive‐breeding program that uses adaptive management to reduce inbreeding and improve captive broodstock performance. A captive‐breeding program was established in 2012 to reintroduce spring‐run Chinook salmon to the southern edge of their range in California's San Joaquin River (SJR), using fish produced each year at the nearby Feather River Hatchery (FRH). We found that the SJR program adequately captured the genetic diversity of the FRH source population and that mate pairings guided by genetic relatedness reduced inbreeding. However, the SJR broodstock reared in captivity had smaller body size at maturity in comparison to the FRH source broodstock which matures at sea, but this effect disappeared when SJR juveniles were released from captivity to mature at sea. Phenotypic traits of SJR female parents also influenced reproductive performance; older mothers and those with smaller eggs had offspring with lower survival. These findings demonstrate that adaptive genetic monitoring and pedigree information can be powerful tools for reducing risks of captive breeding and evaluating program effectiveness.

Substrate Manipulation in Controlled Rearing To Increase Growth and Survival Rate of Holothuria scabra Jaeger

The cultivation of the sea cucumber Holothuria scabra Jaeger for broodstock and production in captivity at sea with naturally available feed, it was reported that the daily growth rate was slow at 0.14±0.10g day-1 (Jasmadi, 2018). One of the efforts to increase growth is substrate manipulation. Organic material in the form of chicken manure has been applied in this study as a mixed substrate with sand at different percentages. Holothuria scabra This study aims to manipulate Holothuria scabra rearing substrates to increase growth. This study used a completely randomized design (CRD) at a 95% confidence level. The research treatments consisted of treatment A (10% organic matter 80% sand), treatment B (20% organic matter 80% sand), treatment C (30% organic matter) 90% sand), D (without organic matter = 100% sand) (100% sand), each treatment was repeated three times. The results showed that the availability of organic matter in the form of chicken manure at different percentages in the sand substrate had a significant effect on growth (P<0.05), but was not significantly different on the survival rate of Holothuria scabra. The growth of Holothuria scabra were better when organic matter is added than without organic matter content in the form of chicken manure. The difference in the percentage of organic matter affects the fulfillment of energy for nutritional needs, so that the availability of energy for growth is also different, but this difference does not affect Holothuria scabra’ survival rate. The difference in the percentage of organic matter content in the form of less or excess chicken manure has been shown to have a negative effect on growth. Furthermore, it is known that treatment B (20% organic matter in the form of chicken manure and 80% sand) per substrate weight has a better effect on growth compared to other treatments. treatment B (20% organic matter in the form of chicken manure and 80% sand) per weight of substrate can be applied to increase growth Holothuria scabra in rearing substrate manipulation. it is recommended that further research be conducted on the period of addition of organic matter, because there are indications of a decrease in organic matter content during the study.

Demographic and genetic consequences of a steelhead supplementation program

AbstractObjectiveSupplementation of naturally spawning populations by the addition of hatchery‐spawned individuals is commonly conducted for recovery of threatened and endangered populations and to support harvest opportunities. Our objective was to evaluate whether the use of a juvenile captive broodstock and an integrated paradigm could increase returns of steelhead, the anadromous form of Rainbow Trout Oncorhynchus mykiss, while avoiding negative genetic impacts commonly associated with hatchery propagation.MethodsWe analyzed 291 genetic markers in adult steelhead returning to an integrated population in southwest Washington over the course of 15 years. Reproductive success (RS) of fish spawning in the natural environment was evaluated by origin (hatchery versus natural) and return year. Data were then pooled over years to maximize sample sizes for comparing RS estimates among groups (i.e., estimation of relative reproductive success [RRS]).ResultWe observed a weak relationship between RS and origin (male p = 0.347; female p = 0.066), but a significant relationship between RS and return year (male p < 0.001, η2 = 0.896; female p ⟨ 0.001, η2 = 0.867) (i.e., hatchery‐ and natural‐origin fish did well or poorly together each year). Estimates of RRS for fish spawned in the hatchery ranged from 2.4 to 6.4, indicating that fish spawned in the hatchery produced more returning adult progeny than did fish allowed to spawn in the natural environment. Estimates of RRS were ⟨1.0 for hatchery‐origin fish spawning in the natural environment, but the difference was nonsignificant for males and marginally significant for females. Hatchery‐origin fish exhibited reduced genetic diversity as well as evidence of increased temporal population structure.ConclusionWe conclude that the program was successful in achieving an increase in adult returns but not in avoiding negative genetic effects on the population and that any lasting impacts of supplementation remain to be determined.

Intestinal lesions and parasites associated with senescence and prespawn mortality in Chinook Salmon (Oncorhynchus tshawytscha).

Prespawn mortality (PSM) presents a major problem for the recovery of spring Chinook Salmon (Oncorhynchus tshawytscha) populations. In the Willamette River, Oregon, PSM exceeds 90% in some years but factors explaining it are not well understood. We examined intestinal tissue samples using histological slides from over 783 spring Chinook Salmon collected between 2009 and 2021, which included tissues from PSM fish, artificially spawned captive broodstock (BS) and normal river run fish, comprised of trapped (Live) and naturally post-spawned river (RPS) fish collected from the river. We observed degeneration of the intestinal epithelium and loss of villous structure, with concurrent severe enteritis. A natural progression of decline in epithelial integrity (EI) through the summer and fall until spawning and subsequent death was also observed. Live fish exhibited high EI scores (mean = 68%), BS exhibited variable EI scores (35%) and RPS exhibited severe loss of EI (14%). PSM fish exhibited prominent loss of intestinal epithelium with EI scores (13%), very similar to RPS fish, despite having been collected earlier in the year. Hence, we argue that low EI scores are strongly linked with PSM. Ceratonova shasta and Enterocytozoon schreckii were common in all groups, but neither were linked to either PSM or a decline in EI.

Effect of Different Levels of Dietary Lipids on Reproductive Performance of Captive Broodstock of <i>Macrobrachium rosenbergii</i>

The present paper reports the results of a laboratory experiment to study the effect of different levels of dietary lipids on reproductive performance of captive broodstock of giant freshwater prawn Macrobrachium rosenbergii. Three formulated pellet diets were prepared containing 2% (D1), 4% (D2) and 6% (D3) lipid and fed to adult females of M. rosenbergii (Av. body weight - 28 g) at 5% of the biomass per day for 60 days. Prawns fed D3 showed significantly higher (P<0.05) weight gain (221.16±6.48 mg/day) compared to those fed D1 and D2. Similarly, significantly higher (P<0.05) reproductive parameters like fecundity (eggs/ g body weight) (1153.6±174.25), egg clutch weight (g) (4.9±0.25) and gonado-somatic index (6.82±0.27) were also found in prawns fed D3. Reproductive effort (g eggs/ female x100), post–hatch fecundity (nos. of larvae/ g female) and mid gut gland somatic index (%) also showed a similar trend. The present results clearly indicated that dietary lipid level of 6% significantly enhances reproductive performance of captive stock of M. rosenbergii compared to 2% and 4% lipid levels.

Induced Sex Reversal in Adult Males of the Protandric Hermaphrodite Centropomus undecimalis Using 17 β-Estradiol: Enhancing Management Strategies for Captive Broodstock

The common snook (Centropomus undecimalis) is a protandric hermaphrodite fish that undergoes a sex change during its life cycle. In nature, common snook females develop directly from males shortly after spawning. However, the factors triggering this process remain unknown. This knowledge gap poses challenges for managing the species in captivity. To address this, we conducted a study on sex change induction in three-year-old males using estradiol and evaluated the potential effects of photoperiod manipulation on early maturation. Four treatment groups were employed: (1) fish with estradiol + natural photoperiod; (2) fish without estradiol + natural photoperiod; (3) fish without estradiol + controlled photoperiod; and (4) fish with estradiol + controlled photoperiod. The effectiveness of these treatments was assessed through histological procedures, which allowed for the examination of the fishes’ gonads. Furthermore, the concentration of alkali labile phosphorus in fish plasma was measured and correlated with the histological results. Our findings revealed that administering 2 mg/kg estradiol implants resulted in a remarkable 100% female population within the estradiol-treated groups. No significant effect on fish maturation was observed due to the manipulated photoperiod conditions. This protocol offers improved management strategies for captive broodstock. Firstly, the concentration of estradiol used in this study proved sufficient to induce sex change in this hermaphroditic species, enabling the production of viable females at an early age and smaller size and facilitating easier broodstock manipulation. Secondly, the implementation of the alkali labile phosphorus technique allows for sex identification without the need to sacrifice the fish. In conclusion, our study provides valuable insights into sex change induction and photoperiod manipulation in common snook. The findings contribute to enhanced management practices for captive broodstock. However, further research is needed to explore the underlying mechanisms triggering sex change and to optimize protocols for long-term maintenance and successful reproduction in captivity.

Comparative study of ovarian development in wild and captive-reared long-whiskered Sperata aor (Hamilton, 1822)

Long-whiskered catfish Sperata aor is a freshwater catfish known for its supreme flesh quality and fast growth, whose captive-reared broodstock denotes a difficult challenge for aquaculture. The reproductive dysfunctions in long-whiskered catfish raised in tank conditions were observed by comparing tissue biochemical composition and ovarian histology of wild female broodstock. Sixty (60) female broodstocks were used in the current study, consisting of 30 reared at sandy-muddy soil tank bottoms in captive conditions and 30 wild individuals collected from the haor basin during the breeding season. The fish reproductive state was investigated using the biometric and reproductive parameters, biochemical composition and levels of amino acids in the different tissues, and histological analysis of ovarian development. Results revealed that the biometrical parameters of wild and captive female broodstocks exhibited no remarkable difference (p > 0.05). Nevertheless, the wild fish had remarkably higher (p < 0.05) GSI (8.73%), oocyte weight (0.45 mg/egg), and ripeness (27.08%) in comparison with captive-reared broodstock. The total length and body weight, body weight and ovary weight, ovipositor diameter and ovary weight, and GSI and HSI displayed a positive relationship with R2 = 1, R2 = 1, R2 = 0.993, and R2 = 0.973, respectively, for wild broodstock, while R2 = 0.994, R2 = 0.806, R2 = 0.804, and R2 = 0.896, respectively, for captive broodstock. Additionally, the proximate composition in oocytes and liver tissues in both broodstocks did not differ significantly (p > 0.05). However, two essential amino acids (EAA), i.e., lysine and phenylalanine, and two non-essential amino acids, i.e., glutamic acid and glycine, were highly significant differences (p < 0.05) in the oocytes and liver of wild broodstock compared to the captive-reared broodstock. On the other hand, the EAA, e.g., isoleucine, threonine, leucine, and arginine, were highly dominated in both wild and captive female brood oocytes and liver. The ovarian histological slides from each fish group showed three oocytes developmental stages that indicated the asynchronous-reproductive ovarian oocytes of this fish. This study may be useful to fully understand the factors affecting the spawning and reproduction of S. aor broodstock, crucial for management in captive conditions as well as conservation and protection for sustainable aquaculture management of S. aor.

Distribution and straying of minijack Chinook Salmon released from a captive broodstock hatchery program

AbstractObjectiveProduction of Chinook Salmon Oncorhynchus tshawytscha in hatcheries can unintentionally produce large numbers of age‐1 males, termed "minijacks," which pose ecological and genetic risks to target and nontarget populations. We evaluated the postrelease distribution of minijacks produced in a hatchery captive broodstock program targeting the White River in the Columbia River basin between 2010 and 2015.MethodsFish were passive integrated transponder (PIT)‐tagged in the hatchery (n = 218,555), and databases were searched to determine movement behavior and final detections on fixed PIT tag antenna arrays during the year in which they were released.ResultTwo main movement behaviors were detected: (1) residuals, which moved solely within the subbasin of release; and (2) migrants, which moved downstream into the Columbia River and then reascended the Columbia River in the year of release. Minijacks that reascended fish ladders in the Columbia River were most often detected at Rock Island and Bonneville dams, the nearest and furthest detection locations downstream of the Wenatchee River. Minijacks were last detected in all locations where spring Chinook Salmon spawn in the Wenatchee River subbasin (seven tributaries and one main‐stem area) and also in the Entiat River (an adjacent watershed); minijacks in eight of the nine locations were considered strays. Estimates of minijacks that strayed outside of the White River were between 61% and 100% annually and were influenced by release location. Minijacks were also more abundant than males of all older ages in some of the tributaries during some years. In addition, they were detected in these tributaries during periods when anadromous adults migrate into spawning areas and when spring Chinook Salmon spawn.ConclusionThe large amount of minijack production and the spatial and temporal overlap could pose genetic and ecological risks to both target and nontarget populations and particularly high straying poses risks to the maintenance of between‐population genetic variability.

Mass synchronization of gonadal maturation in banded knifefish broodstock (Gymnotus cf. carapo)

The banded knifefish Gymnotus cf. carapo (Pisces, Gymnotidae), also known locally as tuvira, is a natural resource of great importance to the Pantanal biome that has been used as live bait in sport fishing. This study investigated the mass synchronization of gonadal development of banded knifefish in captivity by subjecting them to different water electrical conductivity at different time intervals (pre and post conductivity change) and also evaluated the use of ultrasound imaging to identify the sex and phases of ovarian recrudescence of the captive broodstock. Fish were exposed to three different combinations of time intervals (Group 1: 40 + 30 days; Group 2: 45 + 25 days; Group 3: 50 + 20 days) and water conductivity (high: 180 μS/cm, followed by low: 15 μS/cm conductivity, respectively). The control group was kept in low water conductivity throughout the 70-day trial. Based on the results, 93%, 94%, and 86% of mass gonadal maturation of Gymnotus cf. carapo could be achieved by keeping the fish in high water conductivity (180 μS/cm) for 40, 45, or 50 days, and subsequently in low conductivity (15 μS/cm). The sexing and maturation assessment of the fish using ultrasound imaging was fundamental for effectively evaluating the mass gonadal maturation protocol. The combined use of these techniques proved safe in reproductive studies with banded knifefish.

Gonadotropins and Sex Steroid Hormones in Captive-Reared Small Yellow Croaker (Larimichthys polyactis) and Their Role in Female Reproductive Dysfunction.

The seed production of small yellow croaker (SYC) is constrained by reproductive dysfunction in captive-reared females. Reproductive dysfunction is closely linked to endocrine reproductive mechanisms. To better understand the reproductive dysfunction in captive broodstock, functional characterization of gonadotropins (GtHs: follicle stimulating hormone β subunit, fshβ; luteinizing hormone β subunit, lhβ; and glycoprotein α subunit, gpα) and sex steroids (17β-estradiol, E2; testosterone, T; progesterone; P) was performed using qRT-PCR, ELISA, in vivo, and in-vitro assay. The pituitary GtHs and gonadal steroids levels were significantly higher in ripen fish of both sexes. However, changes in lhβ and E2 levels in females were not significant in the developing and ripen stages. Furthermore, GtHs and steroids levels were lower in females compared to males throughout the reproductive cycle. In vivo administration of gonadotropin releasing hormone analogue (GnRHa) significantly increased the expression of GtHs in both dose- and time-related manners. The lower and higher doses of GnRHa led to successful spawning in male and female SYC, respectively. Sex steroids in vitro significantly inhibited the expression of lhβ in female SYC. Overall, GtHs were shown to play a vital role in final gonadal maturation, while steroids promoted negative feedback in the regulation of pituitary GtHs. Lower levels of GtHs and steroids might be key components in the reproductive dysfunction of captive-reared female SYC.

Sablefish (Anoplopoma fimbria) chromosome-level genome assembly.

Sablefish (Anoplopoma fimbria) are in the suborder Cottioidei, which also includes stickleback and lumpfish. This species inhabits coastal regions of the northeastern and northwestern Pacific Ocean from California to Japan. A commercial fishery for sablefish began to flourish in the 1960s, though a downward trend in stock biomass and landings has been observed since 2010. Aquaculture protocols have been developed for sablefish; eggs and sperm from wild-caught and hatchery-reared captive broodstock are used to generate offspring that reach market size in about two years. Parentage analyses show that survival in aquaculture varies among families. Growth rate and disease resistance also vary among individuals and cohorts, but the extent to which genetics and the environment contribute to this variation is unclear. The sablefish genome assembly reported here will form the foundation for SNP-based surveys designed to detect genetic markers associated with survival, growth rate, and pathogen resistance. Beyond its contribution to sablefish domestication, the sablefish genome can be a resource for the management of the wild sablefish fishery. The assembly generated in this study had a length of 653 Mbp, a scaffold N50 of 26.74 Mbp, a contig N50 of 2.57 Mbp, and contained more than 98% of the 3640 Actinopterygii core genes. We placed 620.9 Mbp (95% of the total) onto 24 chromosomes using a genetic map derived from six full-sib families and Hi-C contact data.

Comparison of fatty acid composition of the eggs of wild and farmed Coregonus maraena and the influence of feed

Abstract The fatty acid (FA) compositions of eggs from wild whitefish and captive broodstocks were investigated to estimate the FA requirements of Coregonus maraena. The aim of this study was to increase basic knowledge on the nutritional needs of broodstock. Whitefish eggs from two natural spawning grounds were compared with that of captive broodstocks that were fed three commercially available feeds used in fish farms in Mecklenburg-Vorpommern, Germany. Wild fish eggs differed significantly in crude protein content and FA profiles from the eggs of experimentally farmed fish groups. The percentage of monounsaturated FAs (MUFA) were significantly lower in the wild fish eggs. The most common MUFA was oleic acid in all groups, although in the wild fish eggs the value of it was almost half of that in farmed fish eggs. Wild fish eggs had significantly higher values of total polyunsaturated FAs (PUFA), especially of n-3 PUFA, which was nearly double that of the eggs of the farmed fish groups. Additionally, it was shown that egg FA composition even differed between the wild fish stocks that were from the same area, whereas there were no differences in egg proximate composition or FA composition among the three feeding groups even though the compositions of the feeds fed to these fish differed significantly. The present study suggested that the proportions of essential FAs supplied in the dry feeds fed to the captive broodstocks were inappropriate for this species, and feeds must be adapted further to meet the nutritional requirements of this species to improve the quality of farmed whitefish eggs.

Biochemical composition and adenylate energy charge shifts in longfin yellowtail (Seriola rivoliana) embryos during development under different temperatures

The longfin yellowtail Seriola rivoliana is an emerging species for aquaculture diversification worldwide and production relies on fertilized eggs from captive broodstock. Temperature is the main factor that influences the developmental process and success during fish ontogeny. However, the effects of temperature on the utilization of the main biochemical reserves and bioenergetics are scarcely investigated in fish, whereas protein, lipid and carbohydrate metabolism have critical roles in maintaining cellular energy homeostasis. In this context, we aimed to evaluate metabolic fuels (protein, lipids, triacylglicerides, carbohydrates), adenylic nucleotides and derivates (ATP, ADP, AMP, IMP), and the adenylate energy charge (AEC) during embryogenesis and in hatched larvae in S. rivoliana at different temperatures. For this purpose, fertilized eggs were incubated at six constant (20, 22, 24, 26, 28 and 30 °C) and two oscillating (21⇄29 °C) temperatures. Biochemical analyses were made at blastula, optic vesicles, neurula, prehatch and hatch periods. Results indicated that the developmental period had a major influence on the biochemical composition at any temperature regime tested during the incubation. Protein content decreased only at hatching mainly due to the loss of the chorion, total lipids tended to increase at the neurula period and variations in carbohydrates depended on the particular spawn analyzed. Triacylglicerides were a critical egg fuel during hatching. The high AEC during embryogenesis and even in hatched larvae suggested an optimal energy balance regulation. The lack of critical biochemical changes from different temperature regimes during embryo development confirmed that this species exhibits a high adaptive capacity in response to constant and fluctuating temperatures. However, the timing of hatching was the most critical period of development, where biochemical components and energy utilization significantly changed. The oscillating temperatures tested may have physiological advantages without detrimental energetic effects that will require further research on larval quality after hatching.

Lake Superior Kiyi reproductive biology

AbstractObjectiveThe Lake Superior Kiyi Coregonus kiyi is an understudied species being considered for reintroduction into Laurentian Great Lakes where it no longer occurs. Herein, we provide descriptions of Kiyi reproductive biology with the intention of guiding potential gamete collections for propagation.MethodsData were collected on Kiyi spawning timing, spawning locations, spawning season catch rates, length at sexual maturity, sex ratios, fecundity, egg size, and larval occurrences in Lake Superior from 1996–2021. These data were compared to observations made a century prior in Lakes Michigan, Ontario, and Superior.ResultContemporary Kiyi spawning occurred between late December and late January when surface water temperatures cooled to &lt;4°C. Spawning Kiyi were caught almost exclusively in 38.1‐mm stretch mesh, as compared to larger meshes (50.8–76.2 mm). Capture depths for developing, ripe, running, and spent female Kiyi were similar and ranged from 82 to 221 m. Fifty percent of female and male Kiyi were classified as sexually mature at ~150 mm total length. Fecundity estimates ranged from 1,578 to 6,720 eggs/female. Mean diameter of unfertilized eggs was 1.7 mm. Recently hatched larval Kiyi were collected at the surface during May–July at 62 of the 113 locations sampled throughout the lake in 2019.ConclusionOur work suggests that Kiyi gamete collection efforts from mid‐December through January using 38.1‐mm gill‐net panels set at bathymetric depths of at least 100 m would maximize the collection of spawning Kiyi and reduce the bycatch of other Coregonus species. Future research questions include the following: (1) “Do Kiyi form spawning aggregations at specific spawning areas, or do they spawn indiscriminately across the lake?”; (2) “Do Kiyi spawn near the bottom or up in the water column?”; (3) “What is the relationship between fall lake overturn and Kiyi spawn timing?”; and (4) “Could summer larval and age‐0 Kiyi collections provide an opportunity for establishing a captive broodstock?”

Application of 17α-methyltestosterone to enhance broodstock maturation of the domesticated black tiger shrimp (Penaeus monodon): A comparative study of injection method and oral method

The effects of 17α-methyltestosterone administration on spermatophore quality in captive broodstock of tiger shrimp Penaeus monodon were investigated using injection method and oral method based on the optimized protocol. The experiment was designed to compare the oral administration group and injection group with two replications during a 38-day experimental period. Captive male broodstock of tiger shrimp weighing 57-95 g was collected from ponds and stored in a 10,000 m3 concrete tank (20 shrimp/tank). Male broodstocks were injected and orally administrated with 17α-methyltestosterone at the dose of 300 ng/100 g body weight. Data indicates that the injection of 17α-methyltestosterone showed the percentage of mature broodstock count and the percentage of normal spermatozoa count 1.07 and 1.38% higher and significantly differs from oral administration through mixing in feed at the maturation stage. However, at the time of the maturation and 1st re-maturation of both the methods, the weight of the spermatophores and the number of spermatozoa did not show any difference. Based on the comparison of the two methods used, the results are obtained that the administration of the hormone 17α-methyltestosterone can be done both through mixing in feed and through injection, but the administration of hormones through injection gives better results than the broodstock matures first simultaneously.

Chronic heat stress as a predisposing factor in summer mortality of mussels, Perna canaliculus

Marine farmers have reported increased incidence of mass mortalities of New Zealand green-lipped mussels, Perna canaliculus, grown on near-shore long-line aquaculture farms. While the causative agents remain unknown, die-off events typically occur during the warmest months of the austral summer and appear correlated to unprecedented summer marine heatwaves that have impacted the eastern Tasman Sea in recent years. To further elucidate the role of chronic heat stress as a predisposing factor to ‘summer mortality’, adult P. canaliculus were incubated at 17, 21 and 24 °C for 13 months. Overall biological performance was impacted in the elevated temperature treatments; mean mass gain (Specific Growth Rate) at 17 °C was 0.21% day−1, but fell to 0.18% day−1 at 21 °C and 0.16% day−1 at 24 °C. A survival tipping point was apparent between 21 and 24 °C, with net mortality of 6 and 10% at 17 and 21 °C, respectively, increasing to 100% at 24 °C. Sacrificial gill and haemolymph samples taken every 4–8 weeks showed little evidence of temperature perturbation upon either haemocyte function or the metabolomic profile during the first 4–6 months of incubation. Beyond 6 months, the proportion of haemocytes showing signs of respiratory burst (superoxide-positive) or apoptosis increased steadily at 24 °C, along with a substantial increase in the levels of amino acids frequently associated with anaerobiosis or antioxidant support. During this period, even the more benign temperature treatments of 17 and 21 °C showed increased haemocyte apoptosis and a metabolite profile consistent with increasing protein catabolism. Prolonged exposure to artificially stabilised ‘summer' temperatures therefore appears detrimental to P. canaliculus, with important implications for the operation of captive broodstock conditioning systems. While stable, elevated temperatures up to 24 °C are unlikely to fully account for current observations of summer mortality, disruptions to energy metabolism and immunocompetency are likely to increase the mussels' vulnerability to pathogens and other stressors. On-going research is required to assess the impacts of realistic, fluctuating temperatures, with consideration of the implications for potential pathogens.

CHANGES IN PLASMA LEVELS OF STEROID HORMONES DURING SEXUAL MATURATION OF MALE HELICOPTER CATFISH (WALLAGO ATTU) IN CAPTIVITY

In order to provide reliable indicators of the spawning season of captive helicopter catfish (Wallago attu), this study evaluated the temporal variation in gonadosomatic index (GSI), plasma levels of testosterone (T), and 11-ketotestosterone (11-KT) in male broodstock in captivity. GSI was estimated as the percentage of the relative weight of testis to total body weight. Plasma levels of sex steroids were determined by enzyme-linked immunosorbent assay (EIA). Testis samples were dehydrated and embedded in paraffin, then sectioned at 5 μm thickness. The highest level of T (402.1 ± 16.7 pg/mL) was found in June, followed by a peak in 11-KT level (76.9 ± 4.7 pg/mL) in May. Testes containing the highest concentrations of spermatozoa were observed from June to August. The GSI of males increased significantly from January to June and peaked in July (2.14%). Taken together, we conclude that the spawning season of captive helicopter catfish occurs from June to August. These results will contribute to the basic knowledge of the reproductive biology of helicopter catfish, which can be useful in artificial breeding.

Shrimp shell waste-derived astaxanthin in synergistic combination with its commercial variant augments gonadal maturation and upregulates vitellogenin gene expression of discus (Symphysodon aequifasciatus)

A study was performed to evaluate the efficacy of shrimp shell meal derived natural astaxanthin (SSM), supplemented with its commercial variant on gonadal maturation and vitellogenin gene (Vtg.) expression in reproductively active adults of the high-value ornamental cichlid discus (Symphysodon aequifasciatus) reared under captivity. Four isonitrogenous (50% crude protein), isolipidic (9% ether extract), and isocaloric (400 kcal digestible energy/100 g) experimental diets viz. control (commercial grade astaxanthin, without SSM), T1 (15% SSM + commercial astaxanthin), T2 (20% SSM + commercial astaxanthin), T3 (25% SSM + commercial astaxanthin) were prepared and fed to satiation level twice daily for the entire experimental period of 90 days. Results revealed significant (p < 0.05) linear, quadratic, and overall trends, wherein GSI increased with an increase in the proportion of SSM in the diet, with higher GSI recorded in T2 and T3 treatment groups (testis and ovary, respectively), which were significantly (p < 0.05) different from other groups. The overall linear and quadratic trends of HSI differed significantly (p < 0.05) with the variability in proportions of natural and commercial astaxanthin combinations and were found highest in the T2 treatment group. Cholesterol, FSH, LH, 11-KT, 17β- Estradiol, and 17α-20β DHP levels increased with an increasing proportion of natural astaxanthin and recorded the highest values in the treatment T2 with an overall significant linear and quadratic trend as compared to other treatments. Most of the oocytes of T2 and T3 groups were in the vitellogenic phase, i.e., primary, secondary, and tertiary yolk stages. More spermatids were visible in testicular tubules in T2, followed by T3 and T1. The abundance of Vtg. mRNA was significantly (p < 0.05) evident in T2, followed by T1, then in control. Further increase in SSM inclusion caused a downregulation in the expression of this gene in the T3 group. The dietary combination of SSM @200 g/kg diet with its synthetic/commercial variant exhibited optimum performance at combination levels of 77.5 and 22.5 mg/kg, respectively, evidenced in terms of changes in steroid hormone profiles, gonadal maturation and vitellogenin gene expression in comparison to the control, which contained the dietary synthetic/commercial variant of astaxanthin alone. These inferences are presumably a milestone in the captive broodstock development of this high-value ornamental cichlid, S. aequifasciatus, with an added advantage of cost-effectiveness. The study would help the utilisation of economically important bio-waste in combination with commercial variants for effective value addition in the ornamental fish feed industry.

Efficacy of a Short‐Term Captive Broodstock Program Compared with Hatchery‐Origin Spring Chinook Salmon Derived from the Same Population

AbstractWe examined the efficacy of a one‐generation (five brood years: 1997–2001) captive broodstock program for spring Chinook Salmon Oncorhynchus tshawytscha by comparing survival rates of captive broodstock progeny (CBP; F2) with that of hatchery‐origin fish (HOR) from a conservation hatchery supplementation program in which both groups were derived from the Tucannon River (Washington State) population for the 2000–2006 brood years. Survival rates compared were egg to fry, fry to smolt, egg to smolt, total (ages 3–5) and adult (ages 4+) smolt‐to‐adult‐return (SAR) survival, and total (ages 3–5) and adult (ages 4+) progeny‐to‐parent (P:P) ratio. Total escapement and adult P:P ratios were also examined to determine if observed demographic benefits to the population continued after the captive broodstock program ended. The CBP group had lower within‐hatchery survival than the HOR group, with significant differences in survival at the egg‐to‐fry and egg‐to‐smolt stages due to poor egg viability. Mean untransformed total and adult SARs for the CBP were half those of the HOR group; however, SARs did not differ significantly. The CBP also had significantly lower total and adult P:P ratios than the HOR group and were below replacement for six of the seven brood years. While the captive broodstock provided additional fish for release that would not have been available otherwise, overall the CBP performed poorly and below expectations compared with the HOR group, both within the hatchery and after release. The captive broodstock program provided a short‐term demographic boost, most notable in the 2008–2010 return years, but the benefit did not carry over after the program ended.

Orange Chromide, Pseudetroplus maculatus (Bloch., 1795): A Potential Euryhaline Fish Model to Evaluate Climate Change Adaptations in Fishes

Orange chromide, Pseudetroplus maculatus is a euryhaline species with both ornamental and food value. The species has several attributes similar to other fish model organisms such as smaller size, repeated breeding, ease of maintenance, and higher fecundity. A salinity tolerance study was performed in different salinities (0, 15, and 35 ppt) in triplicate introducing 10 fishes each (5.4 ± 0.08 g) in 12 plastic tanks of 60 L water-holding capacity. Fish were fed with commercial feed (1.2 mm and 40% protein) at 5% of body weight twice daily for 45 days. No significant variation (p&amp;lt; 0.05) in growth and survival was observed during the study indicating the wide salinity tolerance for the species. Experimental breeding of the species in freshwater and seawater (35 ppt) revealed the ability of the species to breed in varying salinities. Lenience in captive broodstock development, pair formation, and year-round natural breeding makes the seed production of the species easier. Characteristics such as multiple spawnings, a prolonged incubation period (48 to 72 hours) useful for elaborative embryonic studies, shorter larval development cycle (25 to 30 days), and better acceptance of live feed (Artemia nauplii and flakes) and commercial feed by the larvae make the species a potential euryhaline ornamental fish model to assess the physiological changes at different salinities. Minimal input requirements and lower capital and operational investments for the seed production of the species make it an ideal model organism for studying the impact of climatic and environmental changes on fish farming in different habitats.