Nitrogenous wastes: often overlooked pollutants in aquatic environments

[Extract] Nitrogenous wastes, including ammonia, nitrite and nitrate, in aquatic systemsoriginate [that is, systems originate] from the runoff of various anthropogenic sources, the decomposition of organic matter and leaching of geological deposits, as well as ammonia being excreted by aquatic animals as a by-product of protein catabolism. To date, most research on these pollutants have been performed from an aquaculture perspective since nitrogenous wastes are a ubiquitous concern under farming conditions. However, they are often overlooked as potential causes for altered distribution and abundance of aquatic animals in the wild, likely due to perceived relatively low levels of nitrogenous wastes in most aquatic ecosystems and the relatively high tolerance of aquatic animals to these pollutants. Nevertheless, recent research is suggesting that these can be inaccurate or biased

Establishing larval feeding regimens for the decorator crab Camposcia retusa: effects of live prey types and density on larval survival and development

Decorator crab Camposcia retusa is a popular marine ornamental species; however, it has never been bred previously. To establish a feeding regime for C. retusa larvae, which include two zoeal and a megalopal stage, three experiments were conducted. In all experiments, >= 60% of unfed 1st zoeal (Z(1)) larvae survived to the next stage, combined with the orange guts observed in larvae fed Artemia, suggesting Z(1) larvae are facultative lecithotrophic. Experiment 1 evaluated the suitability of ss-type rotifer Brachionus rotundiformis as prey. Z(1) larvae were fed rotifer at a density from 0 to 90 ind./ml. There was no significant difference in Z(1) survival among treatments (56.7-68.3%, p > 0.05); therefore, ss-type rotifer is considered an unsuitable prey for the larvae. Experiment 2 examined the suitability and optimal density of Artemia nauplii, and co-feeding copepod Pavocalanus crassirostris with Artemia, for larval rearing. The larvae fed 10 Artemia/ml had the highest survival to megalopae (91.3 +/- 3.1%, p 0.05). Meanwhile, co-feeding copepods with Artemia showed significantly inferior survival and development to megalopae when compared to that of 10 Artemia/ml treatment. Experiment 3 evaluated the effects of Artemia enrichment on larval performance. The results suggested that Artemia enrichment did not improve larval survival or development. Based on our results, Artemia nauplii fed at 10 ind./ml throughout larval development appears to be appropriate for C. retusa

Effects of food concentration and photoperiod on egg production, female life expectancy and population dynamics of the paracalanid copepod, Bestiolina amoyensis

The paracalanid copepod, Bestiolina amoyensis, is a widely distributed species occurring in subtropical inshore waters across the Pacific Ocean. Its small size, herbivorous feeding habit, and high adaptability make the species one of the most promising candidates as potential live feed for hatchery larval rearing. This study investigated effects of different feeding density of microalgae Isochrysis spp. (1 × 105, 2 × 105, 3 × 105, 4 × 105, and 5 × 105 cells ml–1) and photoperiod (8L:16D, 12L:12D, and 16L:8D) on productivity-related parameters, including egg production, female life expectancy and population dynamics of B. amoyensis. Results showed that total egg output over female lifespan, final population size and intrinsic rate of population of 12L:12D photoperiod treatments were always the highest among three photoperiod conditions, especially at the food concentration of 4 × 105 cells ml–1, indicating B. amoyensis had high reproductive performance and the population was in a more stable status. The number of nauplii from 4 × 105 cells ml–1 algal concentration treatment accounted for 75% of the population, and the ratio of females to males approaching 1:1 when photoperiod was 12L:12D; female life expectancy was 10.5 ± 0.6 days. In conclusion, our results showed that Isochrysis spp. is a suitable feed for B. amoyensis with an optimal concentration at 4 × 105 cells mL–1; the optimal photoperiod for B. amoyensis rearing is 12L:12D. The relatively long reproductive lifespan and high intrinsic population increase rate make B. amoyensis a good candidate to develop culture techniques for hatchery larval rearing

Year-Round Spawning, Filial Cannibalism, and Embryonic and Larval Development of the Coral Reef Fish Orchid Dottyback, Pseudochromis fridmani

Aquaculture of marine ornamental fish could potentially reduce the fishing pressure on wild stocks by the global aquarium trade, but its expansion is often constrained by the limited understanding on the biology and early life history of candidate species. The orchid dottyback Pseudochromis fridmani is a valuable and popular marine ornamental fish, but scientific reports on its baseline biology, especially the egg filial cannibalistic behaviour, are scarce. The present study documented key aspects of reproductive biology and early ontogeny of P. fridmani in captivity, including reproductive behaviour, patterns of spawning and filial cannibalism throughout a 12-month period by seven pairs of brood fish, as well as the embryonic and larval development. The results showed that the captive spawning of the broodstock pairs generally occurred every 5–11 days, most commonly every 6–8 days, throughout a year. Despite feeding the brood fish to satiation throughout the data collection period, the average monthly rate of egg filial cannibalism reached 55 ± 37%, but the cannibalism frequency appeared to be pair-specific. The egg incubation duration was approximately 96 h at 27 ± 1 °C, and the development of embryos from cleavage, blastula, gastrula, and segmentation to the pharyngula stage is herein described in detail. The newly hatched P. fridmani larvae possessed important structures and organs for first feeding, including pigmented eyes, developed jaws, and a straight-tube gut. The 0 to 14 days post-hatching (DPH) period appeared to be an important larval stage, as P. fridmani larvae were observed to complete major changes in morphology, gut development, and phototactic behaviour by 14 DPH. Under the culture conditions of this study, the earliest transition to the juvenile stage was observed on 31 DPH, and the majority of fish became juveniles by 56 DPH. The results of this study inform baseline aquaculture production protocols and direct future research, particularly to reduce filial cannibalism through broodstock management and to improve larval culture through supporting the early ontogenetic development of P. fridmani. Additionally, these findings form a foundation for further studying the biology and ecology of P. fridmani in the wild

Editorial: Crustacean reproductive physiology and its applications

[Extract] Crustacea constitute an important taxonomic group in aquatic ecosystems and form an important sector of aquaculture industry. Novelties in studies on crustacean reproductive physiology help shedding new lights on deeper understanding of the mechanisms of sex determination and differentiation of crustaceans. The application of established and innovative techniques based on such knowledge will contribute significantly to progress in the crustacean aquaculture industry. The objective of this Special Issue was to provide a forum for researchers to report upon their cutting-edge research in Crustacean Reproductive Physiology and its Applications. This Research Topic comprises ten original research articles

Profiles of calreticulin and Ca2+ concentration under low temperature and salinity stress in the mud crab, Scylla paramamosain

Calreticulin (CRT) is an important molecular chaperon crucial to survival of organisms under adverse conditions. In this study, the potential roles of CRT in the mud crab, Scylla paramamosain, were investigated. Firstly, SpCRT gene expression was detected in various tissues of S. paramamosain with the highest expression found in the hepatopancreas. To evaluate potential role of SpCRT in cold adaption, sub-adult crabs were subjected to temperatures of 10, 15, 20 and 25 degrees C and the profiles of SpCRT gene were determined in the hepatopancreas, chela muscle and gills. The results showed that the expressions of SpCRT mRNA in these tissues were significantly higher for those crabs exposed to low temperatures of 10 and 15 degrees C as compared to those exposed to the higher temperatures, indicating SpCRT was involved in cold adaptation-probably through facilitating protein folding. When low temperature 10 degrees C or 15 degrees C was further combined with high and low salinity stress, the expression of SpCRT mRNA at low salinity (10 ppt) was in most cases significantly higher than that at high salinity (35 ppt), suggesting that under low temperatures, low salinity may represents a more stressful condition to the crab than high salinity. It was also shown that when crabs challenged by 10 degrees C, Ca2+ concentration increased rapidly in the hepatopancreas and an in vitro experiment further showed that the expression of SpCRT mRNA increased concurrently with added Ca2+ concentration; these results together imply that Ca2+ probably plays a major role in low temperature signaling, which induces expression of genes related to cold adaption, such as CRT

Recent developments in male fertility evaluation, sperm cryopreservation and artificial fertilisation, and their potential application to decapod crustacean aquaculture

To maximise productivity, a better understanding of the underlying causes of subfertility that lead to inferior offspring and high mortality is imperative. In decapod crustaceans, most research has focused on female reproductive performance, with little attention given to male fertility. Paternal genetic contribution is critical to both successful embryonic and post-embryonic development. Assessment of sperm quality can be a direct method to determine male subfertility in decapods. Sperm quality parameters such as sperm concentration and morphology have traditionally been used to determine male reproductive performance, but these procedures are time-consuming and can only assess a limited number of sperm cells and males. Alternative diagnostic biomarkers used widely in humans and other mammals could be adapted to decapod crustaceans and may be more indicative of sperm fertilisation competence and male reproductive performance. These predictive biomarkers use fluorescent cellular dyes and high-throughput flow cytometry or computer-assisted sperm microscopic analysis to evaluate sperm viability, mitochondrial function, acrosome reaction and DNA fragmentation. This review examines current and advanced biomarkers to evaluate sperm quality and further explores state-of-the-art procedures of sperm cryopreservation (conventional vs. vitrification techniques) and artificial fertilisation in decapod crustaceans. Sperm freezing coupled with artificial fertilisation in decapods permits the long-term storage, controlled timing and selection of individuals for reproduction. Collectively, these tools can be applied to commercial broodstock management to improve productivity and accelerate selective breeding in the crustacean aquaculture industry

Influence of Moult Cycles on Digestive Enzyme Activities during Early Larval Stages of Panulirus ornatus

The tropical spiny lobster, Panulirus ornatus, has a complex life cycle characterised by a series of moults that occur throughout pelagic larval stages. Significant morphological, physiological, and biochemical changes commonly coincide with moulting and can have dietary implications when culturing this species. Digestive enzyme activities respond to nutritional requirements and have provided useful insight into nutrient use dynamics associated with first-feeding in P. ornatus. Beyond first-feeding, however, information on digestive enzyme activities in P. ornatus is scarce. Greater knowledge of fluctuations in digestive enzyme activities during moult cycles should facilitate better formulation of feeds and more efficient feeding regimens. As an initial step towards this goal, the present study evaluated the influence of moult cycles on digestive enzyme activities during early larval stages of P. ornatus. The investigation focused exclusively on early larval stages (stages I-III) when delivery of appropriate feeds and nutrition can dramatically affect subsequent growth and survival

Recovery rates for eight commercial sea cucumber species from the Fiji Islands

Determination of the original weight and length of sea cucumbers processed and dried to become bêche-de-mer (BDM), is an important tool in sea cucumber fishery management. The only management mechanism for the sea cucumber fishery in the Fiji Islands is a minimum length prescribed for BDM for export. However, different commercial species have different shrinkage rates during processing and previous studies have suggested modification of fisheries management for sea cucumbers to include species-specific minimum harvest size limits This study determined weight-based and length-based recovery rates (i.e. the length/weight of BDM recovered after processing from the initial length/weight of fresh sea cucumber), for eight commercial sea cucumber species following processing to BDM; White Teatfish (Holothuria fuscogilva), Black Teatfish (Holothuria whitmaei), Tigerfish (Bohadschia argus), Surf Redfish (Actinopyga mauritiana), Hairy Blackfish (Actinopyga miliaris), Stonefish (Actinopyga lecanora), Prickly Redfish (Thelenota ananas) and Sandfish (Holothuria scabra). Length and weight recovery rates varied between species and ranged from the highest recovery values of 54.9% for length and 11% for weight in Black Teatfish, to the lowest recovery values of 32.6% for length and 3.0% for weight in Sandfish and Tigerfish, respectively. Length-based and weight-based relationships were generated for each species through the various stages of processing from fresh to dried (BDM) allowing estimation of initial fresh weight/length from partially or fully processed BDM and vice versa. Information generated in this study provides a basis for developing more species-specific harvest size restrictions for sea cucumbers in the Fiji Islands, and has application in stock assessment studies, estimation of harvest data, monitoring of harvest size limits and standardizing catch data

Redclaw, Cherax quadricarinatus sex-separated rearing strategy enhances reproduction in females

Redclaw crayfish Cherax quadricarinatus, a tropical freshwater species, native to Northern Australia and is regarded as a promising species for global expansion of aquaculture. However, poor female fertility is a hindrance towards the commercial production of redclaw. The present study investigated if dissociated; pre-exposure of female redclaw to males can stimulate spawning and increase reproductive efficiency. The study was conducted in dissociated (111 days) and associated (34 days) phases. Redclaw were held in vertical recirculating aquaculture systems with each system consisting of 42 individual compartments (45 cm length x 33 cm width x 25 cm height) arranged as six compartments horizontally and seven compartments vertically. The average body weight of females was 66 ± 2.2 g. In the dissociated phase, females were either kept alone (0M, n = 36) or were exposed to either 1 (1M, n = 36) or 2 (2M, n = 36) males suspended in the uppermost row of the system. During the associated phase, females (n = 108) were maintained at a sex ratio of 1M:1F. During the dissociated phase, the spawning rate was less in the control compared to the male exposed groups (2.8%, 1/36, 18.1%, 13/72 respectively; p = 0.026). However, the moulting rate was greater in the control compared to the male exposed groups (22.2%, 8/36; 5.6%, 4/72 respectively; p = 0.009). During the associated phase, there were no significant differences in spawning rate (22.2%, 8/36 and 33.3%, 24/72), mean days to spawning (21.88 ± 3.06 and 16.38 ± 2.35), moulting rate (11.1%, 4/36 and 6.9%, 5/72) and mean days to moulting (24.50 ± 3.97 and 22.40 ± 3.93) in the control and male exposed groups, respectively (p > 0.05). However, the mean total number of eggs (670.9 ± 26.0 and 507.0 ± 29.36), fecundity (11.00 ± 0.59 and 6.14 ± 0.47), the hatching rate (89.70 ± 1.31% and 77.50 ± 9.24%) and the total number of juveniles produced (545.70 ± 42.50 and 343.30 ± 37.47) during the associated phase were greater in the male exposed groups compared to the control group respectively; p < 0.05). It was concluded that pre-exposure of redclaw females to males in a dissociated recirculation system, increases spawning rate during a dissociated phase, and after exposure to males improves egg and juvenile production during an associated phase. Such a breeding strategy has potential to increase hatchery productivity