Broodstock management, development of rearing systems, and feeding regimes for larvae of the forktail blenny, Meiacanthus atrodorsalis

The marine aquarium trade is a growing industry supplied largely by an unsustainable wild fishery, sourcing specimens from poorly managed reefs, which are already under threat from increasing anthropogenic activity and rapid climate change. Research into captive breeding and hatchery rearing of popular marine aquarium fish species, underpinned by robust scientific method, has become a key tool to boost sustainability of the worldwide marine aquarium trade, extend our knowledge and understanding of reef fish biology, and aid coral reef research and recovery. Among many popular marine aquarium fish groups the family Blenniidae form one of the 10 most traded marine ornamental fish families and are a prime candidate for research into reliable captive culture. However, little literature exists documenting the biology and breeding techniques of species belonging to this family. Within the family Blenniidae the forktail blenny, Meiacanthus atrodorsalis, is a species displaying good market value, and high potential for aquaculture, making it an ideal model species for investigation into reliable and repeatable captive culture protocols based in scientific method. This thesis addresses key aspects of the captive culture of M. atrodorsalis with particular focus on larval rearing using common hatchery feeds. Chapter 1 reviews the current state of marine ornamental aquaculture (MOA) relative to the recent growth of the marine aquarium hobby, and the concurrent decline of a vast majority of coral reef enviroments worldwide. While research efforts towards captive breeding of marine ornamental species, stands to supplement or replace the supply of wild caught specimens for the marine ornamental trade, and potentially help boost reef recovery efforts through restocking, the MOA sector is still in its infancy. This chapter identifies multiple bottlenecks that persist in limiting the progress of marine ornamental aquaculture, and highlights areas where research efforts should be focused to move forward. Major areas in need of increased research efforts include broodstock management, such as the development of specific broodstock diets and broodstock husbandry, spawning induction via hormone technologies that are tailored to the size and sensitivity of small broodstock ornamentals, and comprehensive, species-specific larval rearing techniques, including system design and larval culture conditions as well as larval feeds and nutrition. In Chapter 2, it was necessary to develop cost effective tank designs to facilitate adequate replication demanded by robust scientific method, while still supporting good growth and survival in Meiacanthus atrodorsalis. Four experimental tank designs were developed to help achieve the aims of this thesis and are described in detail. The four designs increase sequentially in scale and include a 3-L and 9-L rounded tank design, a 5-L modified 'planktonkreisel' design and a 100-L cylindricoconical design, all of which can be operated as either static or flow-through systems. The 3-L and 9-L tanks and the 5-L planktonkreisel design are constructed from readily available materials and can be replicated to improve statistical strength while accommodating the requirements of larval fish for gentle flow, mixing, and maintenance of live prey in suspension. The 100-L tank is a technical improvement on existing current designs, using a novel integrated inlet-outlet design to enable the use of a large central outlet filter to increase screen area. This design is scalable and may be applicable for use in a commercial larviculture setting. While these tank designs were developed primarily to conduct trials on M. atrodorsalis larvae, they displayed potential for use in larviculture of other marine fish species not covered in this thesis. The extent to which the designs supported larval growth and survival of other popular marine aquarium species is presented, highlighting the versatility of these designs to be adapted to a wide range of species and experimental aims. In Chapter 3, the reproductive behavior and embryonic development of M. atrodorsalis was documented, in addition to the growth and development of larvae to settlement stage, using a feeding protocol and live feeds common to fish hatcheries. Courtship and spawning commenced after a series of female and male initiated displays. Adult M. atrodorsalis displayed a preference for shelters of single entrance 50-mm PVC pipe, with a 25-mm reduced entrance, for egg laying, while the male took full responsibility for egg care. Eggs were laid individually with a flattened adhesive plate anchoring them to the walls of the provided shelters. Larvae measuring 3.1 ± 0.2 mm standard length (SL) and 0.63 ± 0.0 mm body depth (BD) hatched approximately 181 h post fertilization (PF) at 28 °C, with a mouth gape height and width of 307.3 ± 11.0 and 263.8 ± 5.5 μm, respectively. By firstly feeding rotifers, and then switching to Artemia nauplii with enriched Artemia metanauplii added later on, newly hatched M. atrodorsalis survived and grew, reaching settlement approximately 35 days post hatching (DPH), measuring 13.5 ± 0.4 mm SL and 3.91 ± 0.3 mm BD. In Chapter 4, two trials were conducted to investigate the survival and growth responses of M. atrodorsalis larvae to varying rotifer densities at first feeding, and times to shift from rotifers to Artemia nauplii. In the first trial, first feeding M. atrodorsalis larvae were offered rotifers at 2, 5, 10 and 20 rotifers mL⁻¹. There was no significant difference in survival and growth between rotifer density treatments, however a density of 10 rotifers mL⁻¹ resulted in the best survival (74 ± 6% at 7 DPH) and was recommended and adopted as a balanced choice to avoid under-feeding and wastage. In the second trial prey offered to M. atrodorsalis was shifted from rotifers (10 mL⁻¹) to Artemia nauplii (3 mL⁻¹) on 3, 6, 9 and 12 DPH. While growth was not significantly different between treatments, survival was highest in treatments switched on 9 and 12 DPH (47 ± 14.3% and 47 ± 11.1%, respectively), suggesting that some larvae were able to ingest Artemia nauplii beyond 6 DPH, with a majority of larvae demonstrating the ability to adapt to an abrupt switch to the new prey beyond 9 DPH. In Chapter 5, two trials were conducted with a continued focus on the timing and method of prey switch. These trials investigated the effect a 3-day co-feeding period and use of a specialty AF Artemia strain, relative to a standard Great Salt Lake (GSL) strain, had on timing the initial switch from rotifers to Artemia nauplii in M. atrodorsalis larvae. A third trial was conducted to investigate the time at which larvae of M. atrodorsalis could be shifted from AF Artemia nauplii to larger enriched GSL Artemia metanauplli. A 3-day cofeeding period improved the survival response of M. atrodorsalis switched from rotifers to Artemia nauplii when undertaken prior to 9 DPH, relative to the trial undertaken in Chapter 4. M. atrodorsalis larvae offered GSL Artemia nauplii could be transitioned as early as 5 DPH, while those offered the AF Artemia nauplii could be transitioned starting as early as 3 DPH when co-feeding was adopted. Larvae fed Artemia nauplii of the AF strain showed 17-21% higher survival, 24-33 % greater standard length and body depth, and 91-200% greater dry weight, after 20 days relative to those fed nauplii of the GSL strain. Meanwhile, enriched Artemia metanauplii of the GSL strain were shown to be an acceptable alternative to AF Artemia nauplii for later larvae, producing similar survival and growth when introduced from 8 DPH. In Chapter 6, three trials were conducted to establish a benchmark regime for weaning and early growout of M. atrodorsalis. The first trial investigated the effect of weaning M. atrodorsalis from live prey to a commercially available marine hatchery diet at 5 different times; starting on 16, 19, 22, 25 and 30 DPH. The second and third trial investigated the effect of 6 different feeding frequencies; 4, 3, 2, and 1 feeds per day, 1 feed every 2 days and one feed every 3 days, and 5 different feed ration sizes; 2, 5, 8, 11 and 15% body weight per day, on survival and growth of M. atrodorsalis juveniles. Weaning M. atrodorsalis from live prey to the formulated diet was successful at all ages tested. However, fish weaned starting 19 DPH and beyond showed 35-54% greater standard length, 28-56% greater body depth and 121-291% greater dry weight, as well as a 30-49% reduction in deformity. High survival on 49 DPH of between 94-97% was achieved when M. atrodorsalis were fed once every 2 days or more frequently from 32 DPH. However, fish fed once per day or more achieved 10-26% greater standard length, 8-29% greater body depth and 54-300% greater dry weight relative to those fed once every 2 days and once every 3 days. Within the feeding rations tested, survival was the highest when fish were fed a ration of 5-15% body weight per day, ranging between 86-93% on 49 DPH. However, there was a clear growth advantage of 18-29% greater standard length, 9-20% greater body depth and 41-160% greater dry weight when M. atrodorsalis were fed a ration of 8% body weight per day or more, relative to a ration of 2 and 5%. In summary, the research presented throughout this thesis describes innovative tank designs to conduct well replicated larval fish research, and goes on to describe reproductive behaviors and techniques, embryo development, and develop a scientifically derived larval feeding protocol for the popular marine ornamental species M. atrodorsalis; a model for the Blenniidae family. While larvae and juveniles of M. atrodorsalis were found to adapt to variation in feeding densities, time and method of prey switchs, live prey quality, time of weaning, feeding frequency, and ration sizes, a balanced approach to rearing was adopted in this thesis to synthesize a reliable feeding protocol. M. atrodorsalis larvae can be reliably reared with good survival and growth following a feeding protocol that consists of rotifers at a density of 10 mL⁻¹ between 0-2 DPH inclusive, followed by newly hatched AF Artemia nauplli starting 3 DPH with a 3 day co-feeding period, then enriched GSL Artemia metanauplii starting 8 DPH with a 3 day AF Artemia nauplii co-feeding period. Weaning onto a formulated diet should take place between 22-25 DPH, after which juveniles are fed at least once per day at a ration of 8% body weight per day. This feeding protocol will produce consistent survival and growth results in M. atrodorsalis up to an age of 49 DPH, balancing key hatchery and research metrics such as cost, food wastage, labor intensity and culture complexity. In conclusion this thesis provides a significant contribution to the commercial and research fields of marine ornamental aquaculture providing innovative tank designs for research and commercial scale aquaculture of marine ornamentals and a comprehensive breeding and larval rearing protocol for a popular marine ornamental species, M. atrodorsalis