Chris M. C. Woods

Preliminary observations on breeding and rearing the seahorse Hippocampus abdominalis (Teleostei: Syngnathidae) in captivity

Abstract A small‐scale preliminary investigation into the breeding and rearing of the seahorse Hippocampus abdominalis Leeson, 1827 in New Zealand was conducted using 12 wildbroodstock. These broodstock were maintained in a hatchery for breeding and the breeding behaviours exhibited by these were observed and described. Over a period of 6 months a total of 12 broods of juveniles were produced. These were then raised on a diet consisting mainly of enriched Artemia for a period of 1 year. After this period juveniles had reached a mean ± 1 SE total length of 110.73 ±0.13 mm, mean ± 1 SE wet weight of 3.07 + 0.23 g, and were reproductively mature. The mean + 1 SE survival per brood after 1 year was 10.57 ± 3.49%.

Improving initial survival in cultured seahorses, Hippocampus abdominalis Leeson, 1827 (Teleostei: Syngnathidae)

Abstract This investigation aimed at improving early juvenile survival in cultured seahorses, Hippocampus abdominalis . Phototaxis from birth until 2 months of age was tested and juveniles were found to be positively phototactic within this age range. A comparison of the effect of culture vessel background (white vs. black vs. clear jars) on feeding efficiency at 1 week and 1 month of age using Artemia as prey revealed an age-dependent effect upon both attack rate and capture success. At 1 week, both attack rate and capture success were higher for juveniles contained in clear jars, and capture success was higher in black jars, as compared with white jars. At 1 month, there was no significant difference in attack rate between different jars, although capture success was higher in clear and white jars than in black jars. In a top-illuminated glass aquarium, juveniles with access to the water surface had lower survival (mean±1 SE=50±4.5%) than those without access to the water surface (73.3±4.2%). This was due to the ingestion of air bubbles when preying on Artemia nauplii congregating near the water surface. For side-illumination there was no such difference. Glass aquaria that were side-illuminated and blacked-off upwards from the waterline supported high juvenile survival (80.4±4.0% per brood) from birth through to 2 months of age in four broods.

Growth and survival of juvenile seahorse Hippocampus abdominalis reared on live, frozen and artificial foods

Abstract The culture of seahorses has usually relied on cultured live foods or collected wild live foods as feed. This can be expensive in the case of culturing live foods and unreliable in the case of harvesting wild live foods. This investigation examined whether juvenile Hippocampus abdominalis from 0 to 2 months of age could be experimentally weaned onto frozen (Cyclop-eeze copepods) and artificial (Golden Pearls) food over 30-day periods with Artemia as a live food control, with 0-, 5-, 10-, and 20-day mixed feeding periods. Newborn juveniles could not be weaned onto Golden Pearls, with almost complete mortality. One-month-old juveniles could be weaned onto Cyclop-eeze with no effect on survival but with lower growth. One-month-old juveniles could be weaned onto Golden Pearls but with lower survival and lower growth. Two-month-old juveniles could be weaned onto Cyclop-eeze but with lower survival and lower growth. Two-month-old juveniles could be weaned onto Golden Pearls with no effect on survival but with lower growth. In all experiments, the rate of feeding strikes on Cyclop-eeze and Golden Pearls was lower than that on Artemia (e.g. range of mean 0.16–0.97 vs. 2.2–2.76 feeding strikes/min), both when Artemia were the sole food presented and when Artemia were cofed with the nonlive foods. However, mixed feeding Artemia with nonlive foods did appear to increase the rate of feeding strikes on nonlive foods. These results indicate the potential for incorporating more cost effective and reliable nonlive foods into seahorse culture.

Visible implant fluorescent elastomer tagging of the big-bellied seahorse, Hippocampus abdominalis

Abstract Wild and captive management of seahorses often requires individual or batch identification. In seahorses this has proven difficult in the past because of the seahorses’ rigid body structure, reduced size of fins and susceptibility to infection. We investigated the suitability of visible implant fluorescent elastomer (VIFE) for tagging the big-bellied seahorse, Hippocampus abdominalis, Leeson 1827. Thirty-six seahorses were tagged and their mortality, growth and tag retention assessed over a period of 7 months together with 36 control seahorses. No tagged or control animal died. In tagged animals growth rate in standard length (SL) was 6% less than untagged animals (non-significant), and growth rate in weight was 10% less than untagged animals (significant) over the experimental period. No tags were lost during the experiment. Tag visibility under LED blue light did not decline significantly although tag detection with the naked eye decreased significantly over the first month of the experiment. Our results show that VIFE is a highly effective batch tagging method for seahorses with minimal biological effects.

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

Abstract 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).

Natural diet of the seahorse Hippocampus abdominalis

Abstract This investigation examined the diet of adult wild seahorses, Hippocampus abdominalis Leeson 1827, from Wellington Harbour, New Zealand. Diet of seahorses (n = 59) collected from shallow subtidal macroalgal stands consisted largely of crustaceans, in particular amphipods (e.g., caprellid and ischyrocerid amphipods), caridean shrimp (i.e., Hippolyte bifidirostris), and peracarids (i.e., the mysid Tenagomysis similis). There were no differences in diet between male and female seahorses. Smaller seahorses consumed a greater amount of crustaceans than larger seahorses, as a result of the greater proportion of amphipods in their gut contents. There were some seasonal differences in diet, with amphipod consumption peaking in spring and summer, and decapod consumption lowest in autumn.

Effect of stocking density and gender segregation in the seahorse Hippocampus abdominalis

Abstract The aims of this investigation were to determine the effects of stocking density and gender segregation on growth and survival of the seahorse Hippocampus abdominalis. Growth and survival of juvenile seahorses (72 mm in standard length and 0.5 g in wet weight) was tested at 1, 2, and 5 juveniles/l and monitored for 60 days. Growth parameters (standard length, weight, and Condition Factor) generally increased as stocking density decreased. There was no difference in survival between 1 and 2/l (mean±1 SE survival=100% and 95.8±2.7%, respectively), but survival in the 5/l treatment was significantly reduced (mean survival=78.3±3.7%). With increasing stocking density, a greater incidence of physical interference between juveniles (i.e. tail-grasping and wrestling) was observed. The effect of gender segregation was tested with sexually mature seahorses in tanks where courtship displays were possible, but egg transfer prevented by limiting tank vertical height. There were no significant differences in growth (standard length, wet weight, Condition Factor, and mean Specific Growth Rate) in males and females either gender segregated or kept together for 90 days. Overall, comparison between males and females revealed no significant differences in growth, apart from the normal difference in wet weight, which begins at the onset of sexual maturity with male brood pouch development. Survival was 100% across all treatments. In addition to courtship displays occurring between males and females kept together, same-sex displays were also observed between males and females and females which were gender segregated, although to a lesser extent, and not always with the full range of courtship behaviours exhibited.

Evaluation of visible implant fluorescent elastomer (VIE) as a tagging technique for spiny lobsters (Jasus edwardsii)

Tagging crustaceans for growth studies is often difficult because external tags/marks may be shed or cause mortalities during moulting. In this investigation, the effectiveness of visible implant fluorescent elastomer (VIE) as an invasive tagging technique for spiny lobsters (Jasus edwardsii) was investigated over a 6-month period. Tagged lobsters were either tagged with the tag running transversely across the ventral abdominal superficial flexor muscle block (transverse VIE) in the second abdominal segment, or in-line with the ventral abdominal superficial flexor muscle block (longitudinal VIE). Non-tagged lobsters were used as the control. At the conclusion of the investigation there were no differences in growth or survival between tagged lobsters and untagged controls and tag retention rates were 100% for both tagging treatments over the 6-month period. Tag visibility was high after six months in both tagging treatments, although higher in the longitudinal VIE treatment. Tag fragmentation was frequent in the transverse VIE treatment, but infrequent in the longitudinal VIE treatment. We conclude that VIE is an effective tagging technique for J. edwardsii in terms of the high degree of tag visibility, retention, and non-detrimental impact on the growth and survival of tagged animals, provided the VIE tag is injected in-line with the orientation of the muscle fibres/tissue.

Reproductive output of male seahorses,Hippocampus abdominalis,from Wellington Harbour, New Zealand: Implications for conservation

Abstract This investigation examines aspects of reproductive output in brooding wild male seahorses, Hippocampus abdominalis, from Wellington Harbour, New Zealand. Previously undocumented, such information is crucial to the management and protection of this species in relation to the CITES Appendix II‐listing of all seahorse species. Brooding males (n = 46) were captured and kept captive until the release of their juveniles, whereupon the number of juveniles was counted and sampled for standard length (SL) and dry weight (DW). SL (mean ± 1SE) of brooding males was 18.1 ± 0.6 cm and wet weight (WW) 17.6 ± 1.6 g. Number (mean ± 1SE) of juveniles released per brood was 271.2 ± 27. The number of juveniles produced was positively correlated with parent SL, WW, and brood pouch volume. Brood pouch volume was positively correlated with male SL. SL (mean ±1SE) of juveniles released was 16.7 + 0.2 mm and DW 1.2 ± 0.1 mg. Mean SL and DW of juveniles were not correlated with the number of juveniles per brood, parent male SL or parent male pouch volume. The percentage of pouch contents which were non‐viable (i.e., premature or non‐viable eggs) upon juvenile release was low (1.1 ± 0.2%; mean ±1SE of the total pouch contents). Based on findings in this study it is suggested that the CITES 10 cm minimum height restriction, which can be used in lieu of non‐detriment findings to allow sustainable exploitation of seahorses, is not suitable for H. abdominalis from Wellington Harbour as it would appear to only protect small males that produce low numbers of juveniles.

An observation of the turbellarian Paravortex sp. in the New Zealand scallop Pecten novaezelandiae (Bivalvia: Pectinidae)

Abstract In a novel association the turbellarian rhabdocoel Paravortex sp. was observed in a group of the scallop Pecten novaezelandiae. Flatworms were more frequently observed in gaping and dead scallops, although the average density of flatworms in infested scallops was low. Scallops which were non‐gaping contained very few flatworms. Flatworms occurred throughout the entire digestive system of the scallops with the majority found in the intestine.