Growth of cultured seahorses (<Emphasis Type="Italic">Hippocampus abdominalis</Emphasis>) in relation to feed ration

This investigation examined the effect of varying feed ratios on cultured seahorse (Hippocampus abdominalis) growth and survival using frozen mysids (Amblyops kempii) at daily feed rations of 5, 10, 15 or 20% wet body weight. Feeding these different feed rations did not result in any significant difference in seahorse standard length after 3 months. However, seahorses fed the 10–20% rations were heavier and with higher condition factor (CF). Based on the total amount of frozen mysids offered to the seahorses, the food conversion ratio (FCR) became less efficient with increasing feed ration. However, when the actual mysid consumption was factored in there were no significant differences in FCR. There was a significant difference in daily specific growth rate (SGR), with the 5% ration having the lowest SGR. On a cost/benefit basis, based on the total amount of mysids offered the most cost effective ration for daily length and weight increase was the 5% ration. With actual mysid consumption taken into account, cost/benefit value favoured the 5 and 10% feed rations. Survival was 100% across all treatments. Based on this, a feed ration of 5–10% wet body weight per day of frozen mysids is recommended for cultured H. abdominalis     

Frozen mysids as an alternative to live Artemia in culturing seahorses Hippocampus abdominalis

This investigation examined the effects on growth and survival of seahorses Hippocampus abdominalis Leeson 1827 fed a 25% body weight (wet weight) daily ration of live Artemia sp. enriched with Algamac‐3050, frozen mysids Amblyops kempi or a combination of live enriched Artemia and frozen mysids. After 3 months there was no difference in seahorse length, wet weight, condition factor (CF), or food conversion ratios (FCR) between the treatments. Mean daily specific growth rate (SGR) was higher for the Artemia‐only treatment than for the mysid‐only treatment (P<0.05). FCRs ranged from 6.14 g to 8.72 g dry weight of food required to give a 1‐g dry weight increase in seahorses. There was no difference in survival between treatments. Fatty acid analysis revealed that mysids had a higher percentage composition of EPA, 20 : 5n‐3, and DHA, 22 : 6n‐3, but a lower composition of AA, 20 : 4n‐6, than enriched Artemia. Percentage n‐3 highly unsaturated fatty acids (HUFAs) in mysid levels were approximately twice that of Artemia. Proximate analysis revealed mysids to be higher than the enriched Artemia in protein and fats, and lower in water content. This experiment demonstrates that, although no growth advantage was derived from the use of frozen mysids, they can be used successfully as an alternative food to live enriched Artemia for H. abdominalis. The use of frozen mysids is highly recommended in commercial seahorse culture if the seahorses are to be sold into the live aquarium trade, as this may increase their chances of survival after sale.     

Effect of Direct Transfer to Different Salinities on Early Juvenile Pot‐bellied Seahorse,Hippocampus abdominalis,Survival in Culture Conditions

In Tasmania, commercial seahorse culture takes place in tank systems in which approximately 75% of the water is exchanged daily from the Tamar River estuary. The aim of this study was to examine the effect on survival of early juvenile pot‐bellied seahorses, Hippocampus abdominalis, directly transferred and cultured for 9 d in salinities of 5, 10, 15, 20, 25, and 32 g/L. Direct transfer of seahorses to 5 g/L salinity resulted in 100% mortality within 7 d. After 9 d, an improvement in survival was recorded in seahorses cultured in 10 and 15 g/L compared to those cultured in 25 and 32 g/L salinities. This study is the first to report on the tolerance of H. abdominalis in captivity at salinities as low as 10 g/L in early life stages without compromising survival.     

Long‐term Effects of Passive Integrated Transponder Tagging on the Growth of Olive Flounder,Paralichthys olivaceus

The effects of passive integrated transponder (PIT) tagging on the growth and survival of olive flounder, Paralichthys olivaceus (initial average mass ± SD: 502 g ± 14.3), were examined for 8 mo. Tag readability in relation to implant position (eyed‐side muscle, blind‐side muscle, and peritoneal cavity) was also documented. The overall weight gain of fish tagged in the eyed‐side muscle (444 g) was significantly less than control and tagged fish in the blind‐side muscle and peritoneal cavity, which showed 470–488 g of weight gain (KW, P < 0.001, N= 78, df = 3). Specific growth rates (%/d) did not differ significantly (P > 0.05) among control, blind‐side muscle, and peritoneal cavity groups. No significant (P > 0.05) difference in survival rate was found between treatment and control. The readability of PIT tags in all implanted positions was 100%. The average time spent tagging at each position was less than 30 sec. These results show that PIT tagging of olive flounder weighing approximately 500 g in the blind‐side muscle and peritoneal cavity is feasible and reliable with fewer negative effects on growth than observed on the eyed‐side muscle site trial.     

Striking a balance between retaining populations of protected seahorses and maintaining swimming nets

• 1. The fish family Syngnathidae (seahorses, pipefish, pipehorses and seadragons) is fully protected in New South Wales, Australia, but in some countries certain species are threatened by unsustainable collecting, capture as incidental bycatch, and habitat degradation.
• 2. Within Sydney Harbour, two species of seahorses (Hippocampus abdominalis and Hippocampus whitei) have been found to colonize artificial structures such as jetty pylons and protective netted swimming enclosures. These protective nets are subject to fouling from epibiotic growth (algae, ascidians, bryozoans, etc.) and rubbish, which causes the nets to collapse from the additional weight. Local authorities employ diving contractors on an ad hoc basis to remove the epibiota from nets.
• 3. Surveys showed a significant decline in the numbers of both seahorse species at one site following the replacement of a net, and recovery of the H. whitei population took more than 15 months.
• 4. A manipulative experiment tested the importance of epibiotic growth for seahorses. H. whitei, tagged with individual marks, were allocated to sections of a net that had undergone different cleaning procedures. Seahorse size, position on the net and total population abundance were recorded every 2 weeks over a 3 month period. It was demonstrated that seahorses have a significant positive association with epibiotic growth and proximity to the sea floor. Seahorse populations also showed seasonal variation in abundance with increased numbers on the net during the breeding season (spring–summer).
• 5. This project has led to the development of best practice net cleaning procedures for local authorities in Sydney Harbour to manage growth on the nets while minimizing impacts on seahorse populations. Copyright © 2009 John Wiley & Sons, Ltd.

     

Effects of Anesthetic Disposal on the Physiological and Behavioral Responses of the Lined Seahorses,Hippocampus erectus

Anesthetic disposal for fish often results in physiological and behavioral responses. There is limited information involved on the metabolic and behavioral responses of the seahorses. The lined seahorse, Hippocampus erectus, is of great interest in the sciences because of its unusual S‐shaped morphology and male pregnancy behavior. This study found that the lined seahorse could be effectively anesthetized into Stage II at the concentrations of 10 mg/L clove oil or 20 mg/L MS‐222 based on the comparison of six different treatments. The ventilation frequency, oxygen consumption, and ammonia‐N excretion of the seahorses were decreased significantly as soon as they were exposed to the anesthetic agents. A higher O : N ratio was found in seahorses anesthetized by clove oil as compared to those exposed to MS‐222. After the anesthetic treatment, the feeding frequencies of recovered seahorses were low at the beginning and then increased during the 7‐d culture. Moreover, there was no incremental difference of wet weights among the tested seahorses (P = 0.534). The findings indicate that the anesthetic process has few effects on the feeding and short‐term growth of seahorses in spite of the occurrence of physiological and behavioral responses.     

Effect of Temperature on Growth and Survival in Cultured Early Juvenile Pot‐bellied Seahorses,Hippocampus abdominalis

In Tasmania, Australia, commercial seahorse culture takes place in tank systems in which approximately 75% of the water is exchanged daily from the Tamar River estuary. As such, some water conditions such as temperature fluctuate on a daily and seasonal basis. The aim of this study was to examine the effect on growth, condition, survival of, and Artemia ingestion by, early juvenile seahorses, Hippocampus abdominalis, cultured for 6 wk at temperatures within the species' natural range (8–24 C) and above it (26 C). Seahorses cultured at 20 C were longer and heavier than those at 17 C, although not significantly different to 23 C. There were no differences in survival or Artemia ingestion of juveniles cultured at 17, 20, and 23 C. At 26 C, 100% mortality was reached on Day 15. This study demonstrates that H. abdominalis can be reared in captivity at a range of 17–23 C in early life stages without compromising growth and survival.     

Effect of stocking density and photoperiod on growth and survival in cultured early juvenile pot‐bellied seahorses Hippocampus abdominalis Lesson, 1827

The effect of stocking density and photoperiod on Hippocampus abdominalis was examined in this study. Stocking densities of 45, 30, 15 and 5 seahorses 3 L^?1 were tested on newborns. Growth and survival were independent of stocking density. A second stocking‐density experiment aimed to remove the effect of an early mortality experienced in experiment 1 using older juveniles at 25, 15 and 5 seahorses 3 L^?1. There were no differences in the parameters measured. Also, the effect of photoperiod was investigated on seahorses cultured under 24:00, 16:08 and 08:16 (L:D) photoperiods. A single Artemia meal was delivered at 10:00 hours. Survival and body growth in 16:08 and 08:16 hours were higher than in 24:00 hours. In a second experiment, seahorses were cultured in the photoperiods and conditions described for experiment 1, except they were fed twice the amount in two meals delivered at 10:00 and 16:30 hours. The seahorses in 16:08 hours showed better growth than the other treatments, but there were no differences in survival. These results suggest that early juvenile H. abdominalis can be cultured at higher stocking densities than previously reported, without compromising growth and survival, and when feeding was not limiting, grew better in an extended photoperiod (16:08) but not in 24:00 hours.     

Substrate‐attachment Preferences of Cultured Newborn Pot‐bellied Seahorses,Hippocampus abdominalis (Lesson, 1827)

During a series of observations, newborn pot‐bellied seahorses, Hippocampus abdominalis, were offered three size choices of diameter and density of substrate. The seahorses exhibited a marked preference for the greatest diameter and the lowest density substrates.     

Biochemical composition of wild and cultured seahorses (Hippocampus kuda Bleeker)

The seahorse has been used for thousands of years as an important traditional Chinese medicine (TCM) in China. Many species of wild seahorse have become endangered, but demand for them continues to grow rapidly. Therefore, it is urgent to cultivate seahorses to relieve the strain on natural populations and meet the market demand for this TCM. In this study, medicinal components of wild and cultured yellow seahorses (Hippocampus kuda Bleeker) were analysed and compared. Different parts of the body (cortex and bone), male and female specimens, and seahorses of different ages were analysed. Crude protein, crude fat, trace elements, calcium, amino acid, fatty acid, steroid and cholesterol content were measured. The results showed that moisture content accounted for 70% of wet weight and ash content increased with growth. Crude protein and fat contents were higher in cultured seahorses than in wild specimens, and the content of Zn in cultured seahorses (93.26 ± 10.44%) was significantly higher than that of same‐aged wild seahorses (74.20 ± 3.83%). Amino acid and fatty acid contents of cultured seahorses also were higher than those of wild seahorses. These findings show that cultured seahorses can also be used in TCMs and that 1‐year‐old cultured seahorses have the best properties.     

Ontogeny of digestive enzymatic capacities in juvenile seahorses Hippocampus guttulatus fed on different live diets

Differences in survival and growth rates in seahorse Hippocampus guttulatus juveniles feeding on Artemia sp. or copepods have been related to specific digestive capacities of seahorse newborn, which are capable of actively forage on available prey from the first day of live. Other seahorse species, such as H. abdominalis and H. hippocampus, show high success feeding on Artemia nauplii suggesting species-specific differences in the digestibility of prey among seahorses. In this study, the profiles of digestive enzyme activity during the initial 15 days after release (DAR) were very low for trypsin, chitinase and α-amylase. In contrast, higher activities towards any of the assayed substrates for lipase (butyrate, octanoate and oleate) were evident from 0 DAR onwards. From 15 DAR onwards, the effect of diet composition became evident in juveniles previously fed on a mixed diet (Artemia + copepods), which showed a clear increase in all the assayed enzymes when compared with juveniles fed on Artemia as a sole prey. As a practical applicability of this study, a feeding schedule ensuring an adequate digestibility of the prey is proposed based on ontogenetic enzymatic activities of seahorse juveniles fed on different prey.     

Identification and characterization of the pathogen associated with skin ulcer syndrome in lined seahorse,Hippocampus erectus

The lined seahorse, Hippocampus erectus, is an Atlantic species, which mainly inhabits shallow sea beds or coral reefs. Seahorse has become very popular in China due to its wide use in traditional Chinese medicine (TCM). However, the aquaculture of the lined seahorse has been threatened by a variety of diseases, especially bacterial infections. Skin ulcer syndrome becomes more and more common in the culture of seahorses, leading to skin ulcer, liver erosion and minority tail rotting. These diseased seahorses die in only 72 hr, causing huge economic losses in aquaculture. Pathogen HMT‐1 was isolated from the lined seahorses with skin ulcer syndrome, which was identified as Vibrio harveyi. The median lethal dose (LD₅₀) of HMT‐1 was 2.88 × 10⁸ cfu/ml. The pathogenic mechanism of HMT‐1 was preliminarily studied, and the pathological changes of the diseased lined seahorses were also investigated. Moreover, the activities of ACP, complement 3, SOD and LZM at different time post injection were measured by commercial kits. Our findings can provide reliable reference for diagnosis and treatment in the future.     

Effectiveness of four methods for tagging juveniles of farm-reared gilthead sea bream, Sparus aurata, L.

This study tested different tags for each size of farm-reared gilthead sea bream, Sparus aurata L. juveniles, used in enhancement programmes. The following tags were tested: dye mark, fingerling tag, opercular tag, anchor tag A (filament diameter of 1.20 mm) and anchor tag B (0.85 mm). Tag/mark retention, wounds produced by the tag, ease of application, ease of detection and cost were examined. Epidermal dye marks had poor retention and detection rates. Of the tags tested, retention was greater for the anchor tag A (80–100%) after 7 months; anchor tag B showed a retention rate of only 20% after 3 months. The fingerling tag had a retention rate of 27.5% after 12 months. The opercular tag had a retention rate of 44% after 20 days but fractured the opercular bone in many cases. Tag incisions and wounds persisted in some fish for the duration of the experiment.     

Swimming nets have positive effects on populations of the endangered White's seahorse Hippocampus whitei

1. Habitat degradation and destruction arising from rapidly increasing urbanization represents one of the most significant threats to biodiversity. Human populations are continuing to increase around coastal regions, and as marine habitats are displaced by artificial structures it is important to understand how marine species may be impacted by these changes in habitat availability. The endangered seahorse Hippocampus whitei has been observed inhabiting protective swimming nets in Sydney Harbour, Sydney, Australia, even in the presence of natural habitats.
2. This study tested whether the presence of a swimming net results in increased seahorse numbers at sites around Sydney Harbour, or whether seahorses are attracted away from natural habitats. Density surveys and mark–recapture population estimates were done at sites with pre-existing swimming nets and compared to control sites where only natural habitat was present. A manipulative experiment was conducted in which panels of swimming net material were installed at two sites in Sydney Harbour, with comparisons to control sites over a period of 14 months (April 2018 to June 2019) to test whether the installation of swimming nets would affect seahorses on surrounding natural habitat or increase site abundance.
3. The pre-existing and installed swimming nets were found to support greater densities of H. whitei as well as some increases in site-scale abundance, with no effects on seahorse density on natural habitats. It is likely that increased seahorse production is occurring on the nets, with no evidence that seahorses are being attracted away from natural habitat; however, effects may vary across survey occasions and sites. Furthermore, swimming nets may serve as a useful replacement habitat in locations where natural habitat has become sparse or absent.

     

Effects of varying Artemia enrichment on growth and survival of juvenile seahorses, Hippocampus abdominalis

Seahorses are the focus of recent aquaculture ventures in a variety of countries. Many of these ventures utilise enriched live Artemia (to varying degrees) to feed their seahorses. Given the range of commercially available enrichment products that can be used to enrich Artemia, it is imperative to determine which of these may promote the best growth and survival in seahorses, as well as being most cost-effective. This investigation tested the effects on juvenile seahorse (Hippocampus abdominalis Leeson, 1827) growth and survival through enriching Artemia with three commercial enrichment products: Super Selco®, DHA Protein Selco® and Algamac-3050. These were tested against a low-cost Artemia on-growing mixture used in this instance as an enrichment (90% Eyre Peninsula Aquaculture brine shrimp food (EPABSF)/10% spirulina).

After 3 months, there was a significant difference in juvenile length between the enrichment treatments, with juveniles in the DHA Protein Selco® and Algamac-3050 treatment longer than juveniles in the Super Selco® treatment, but not longer than juveniles in the EPABSF/spirulina treatment. There was also a significant difference in juvenile wet weights between the treatments, with juveniles in the Super Selco® treatment weighing significantly less than juveniles in the other three treatments.

In terms of condition factor (CF), there was a slight significant difference between the treatments, with juveniles in the DHA Protein Selco® and EPABSF/spirulina treatment having higher CFs than juveniles in the Super Selco® treatment, but not the Algamac-3050 treatment. Mean daily specific growth rate (SGR) for Super Selco® was lower than the other three treatments. There was no effect of enrichment treatment on seahorse survival with 100% survival in all four treatments.

Fatty acid analysis revealed marked differences in the Artemia enriched with the various enrichment products. Super Selco®- and Algamac-3050-enriched Artemia had the highest percentage of docosahexanoic acid (DHA), 22:6(n−3), while Super Selco®-enriched Artemia had the highest percentage of eicosapentaenoic acid (EPA), 20:5(n−3). EPABSF/spirulina-enriched Artemia had the highest percentages of C18 fatty acids. Percentage of polyunsaturated fatty acids (PUFA) and n−3 PUFAs were highest in Super Selco®- and Algamac-3050-enriched Artemia. Proximate analysis revealed little difference among all four enrichment treatments in terms of protein, fat and carbohydrate levels.

The results from this experiment demonstrate that when culturing H. abdominalis, all three commercial enrichment products produce good seahorse growth and excellent survival. However, on a cost/benefit basis, all three commercial products were outperformed by the cheaper Artemia on-growing mixture (EPABSF/spirulina).     

Effects of tagging on migration behaviour,survival and growth of hatchery‐reared Atlantic salmon smolts

The effects of four different tagging methods (PIT, anchor T‐tag, Carlin tag and dummy radio transmitter) on survival, behaviour and growth of Atlantic salmon smolts during their downstream migration were examined in semi‐natural circular channels during a natural migration period in spring. Survival of smolts was high and tagging wounds healed well in all tagging groups. Tag loss rates were generally low, being the highest (2.5%) in the dummy radio transmitter group. Total length and body mass of the tagged and untagged smolts did not differ at the end of the experiment. Migration activity of smolts generally showed similar patterns among the treatments. However, Carlin‐tagged smolts started their migration slightly later than the PIT‐tagged fish, and smolts tagged with Carlin tag or dummy radio transmitter showed less overall migration activity than fish with PIT tag.     

Tagging: on the use of passive integrated transponder (PIT) tags for the identification of fish

To determine the efficacy of passive integrated transponder (PIT) tags for marking rohu Labeo rohita (Ham.) in the selective breeding programme, a series of experiments has been carried out at the Central Institute of Freshwater Aquaculture (CIFA) under the Indo–Norwegian project of ‘Selective breeding of rohu’. Six groups of rohu fingerlings with weight ranging from 2 g to 20 g were tagged with PIT tags to determine a suitable size range for tagging. Fingerlings weighing 8–15 g were found to be quite suitable for tagging with a PIT tag. Recovery of the PIT tag depends upon the survival of tagged fish under field conditions. Rejection of the PIT tag by rohu was observed to be only 0.05%. Through effective management practice, the survival of tagged fish increased up to 95%, and thus tag loss was minimized.     

Preservation causes shrinkage in seahorses: implications for biological studies and for managing sustainable trade with minimum size limits

• 1. The implications of shrinkage associated with desiccation and ethanol preservation for seahorses (genus Hippocampus) were investigated using Hippocampus guttulatus (European long‐snouted seahorse) as a model. Specifically, this research addressed the implications of preservation for taxonomy and life history studies and the application of minimum size limits (MSL) for managing seahorse trade.
• 2. In 2004, the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) listed all seahorse species on its Appendix II, and recommended a 10 cm MSL as an interim means of ensuring sustainable international trade. Inconsistencies in seahorse measurement methods and repeatability posed challenges for applying the MSL. Moreover, the shrinking effect of desiccation on body length observed in other fish was assumed to be negligible for seahorses because of their high degree of ossification.
• 3. Changes in seahorse sizes were measured following immersion in ethanol and desiccation. H. guttulatus shrank on average by 0.1–2.3% when preserved in ethanol and 3.0–6.4% when dried, depending on the trait measured. Similar trends were observed in a sample of H. kuda (yellow seahorse). Specimen posture during drying, and measurement methods also influenced estimates of size.
• 4. Based on the shrinkage observed, 14–44% of captured seahorses that are dried could shrink to below the recommended MSL, even if all seahorses were longer than the MSL at capture. This demonstrates that small changes in body lengths can have significant implications for trade of species managed with size limits.
• 5. Recommendations are to (1) standardize seahorse measurement methods, (2) consider the effects of preservation and measurement technique on body lengths, and apply appropriate corrections in comparative studies and when developing fisheries management strategies, and (3) adjust size limits at the point of capture to ensure retained seahorses comply with the CITES recommended MSL.

Copyright © 2008 John Wiley & Sons, Ltd.     

Prey Selectivity and Trophic Behavior of the Patagonian Seahorse,Hippocampus patagonicus,in Captivity

This study aims at evaluating the Patagonian seahorse, Hippocampus patagonicus, feeding behavior in captivity with regard to type and size of prey selectivity and time‐investment‐related activities for searching and capture. Experiments in aquaria were carried out under two different treatments, with and without refuge for prey. Different diets composed of amphipods (Melita palmata and Ampithoe valida), juvenile decapods (Neohelice granulata) from natural environments, and artificially cultured Artemia salina. The eaten prey’s size was analyzed and experiments with size‐controlled prey were carried out. There were neither significant differences in the prey quantity ingested between males and females nor between treatments (with or without refuge). However, significant differences were found between the quantities of each prey consumed. Amphipods and A. salina were consumed in greater quantity (P < 0.05) when compared with juvenile decapods. Experiments with A. salina of different sizes did not show significant differences on seahorses’ preference. N. granulata was highly avoided and seahorses had lower capture efficiency over this prey. Behavioral observations showed that more than 50% of the times seahorses were resting and ambushing their prey. In captivity, with optimal conditions for predation, the Patagonian seahorse modifies its opportunistic behavior, feeding selectively, and bases its food preferences on prey size and shape .     

Tagging effects on three non-native fish species in England (Lepomis gibbosus, Pseudorasbora parva, Sander lucioperca) and of native Salmo trutta

Abstract –  To address the dearth of information on tagging effects and long-term survivorship of tagged fish in native and introduced species, laboratory and field investigations were undertaken on three non-native fish species (pumpkinseed Lepomis gibbosus ; topmouth gudgeon Pseudorasbora parva ; pikeperch Sander lucioperca ) tagged with coded-wire (CW), passive integrated transponder (PIT), radio (RT) telemetry and/or acoustic tags (AT), with survivorship of native brown trout ( Salmo trutta ) examined in the field. Laboratory results revealed high survivorship following tag attachment/insertion and resumption of feeding within 24–48 h of tagging (all mortalities could be attributed to an unrelated outbreak of fungal infection), with retention rates being high in both pumpkinseed and pikeperch but low in topmouth gudgeon (excluded from field studies). In the field, short-term post-operation survival was high in pikeperch, pumpkinseed and brown trout. In pumpkinseed and trout, 100% of RT fish survived a 24–30 day tracking study, with 60% and 80%, respectively, recaptured alive at least 3 months post-tagging. Of PIT tagged pumpkinseed, 44% were recaptured (after 6–18 months), with small-sized, CW-tagged fish (0.38 g weight) captured up to 1 year after tagging. In pikeperch, all AT fish except one (the smallest specimen) survived their full expected tracking period (i.e. tag life) – the single lost specimen survived at least half of its expected tracking period (i.e. 6 month battery life). Overall, the tagging methods used were highly effective in pumpkinseed and pikeperch, showing good retention and survival, but PIT tagging of topmouth gudgeon was plagued by low survivorship and tag rejection.