ENDOSCOPY APPLICATION IN BROODSTOCK MANAGEMENT OF ARAPAIMA GIGAS (SCHINZ, 1822)
SHORT COMMUNICATION Submitted: May, 2015
Accepted: August, 2015
Published in: Journal of Applied Ichthyology 32 (2016), 353-355
Torati, L.S.; Varges, A.P.S.; Galvão, J.A.S.; Mesquita, P.E.C. & Migaud, H.
Breeding and Physiology team, Institute of Aquaculture, School of Natural Sciences, University of Stirling, FK9 4LA, Stirling, Scotland, UK.
Contributions: The present manuscript was compiled in full by the author of this thesis (LT). Experiment was conceived and designed by LT and HM. Examinations were carried out by LT, AV, JG and PM. All authors approved the final version of the manuscript.
4.A.1. Introduction
The air-breathing fish Arapaima gigas (Schinz, 1822) is an emblematic species of the Amazon with adults reaching up to 2.5 m in total length. It has long been considered as a promising new candidate species for aquaculture, with reported growth rates of 10 kg over one year, no intramuscular bones and suitability to different production systems.
However, the control of reproduction in captivity is a key bottleneck limiting the expansion of the aquaculture sector mainly due to the lack of fingerling supply, which also increases the pressure on the natural stocks.
Sexual maturity is reached after three to five years, when only the left gonad becomes functionally developed (Godinho et al., 2005). The oocyte development is asynchronous and spawning can occur several times in a same reproductive period, usually during the rainy season from November to April in the Amazon (Núñez et al., 2011). During this period, couples seek shallow flooded regions for nest building and mating (Castello, 2008b). In captivity, reproduction is stimulated by isolating couples in earth ponds, but this strategy is ineffective with only few spawns usually obtained. One of the main reasons for such unreliable reproductive control is the absence of consistent sexual dimorphisms between genders and the lack of tools to assess fish reproductive status. Broodstock pairing is therefore done without accurate information on gender and reproductive condition.
In many fish species, cannulation is routinely used for gonad biopsy and assessment. However, in some species like sturgeon, specialised endoscopic equipment has been successfully used with minimal body incisions (Hernandez-Divers et al., 2004).
Interestingly, endoscopic techniques can also be used to navigate through the gonoduct (gonoductoscopy) (Divers et al., 2009). In A. gigas, cannulation for gonad assessment is impossible due to its atypical gonadal morphology (Núñez et al., 2011). Females have a
left gymnovarium lacking a capsule, therefore mature oocytes are released directly into the coelomic cavity, which guides them into an elongated structure called ligament (“oviduct”) that conducts oocytes externally to the genital papilla (Godinho et al., 2005).
The aim of this study was to test a non-invasive gonoductoscopy in A. gigas broodstock, taking advantage of modern endoscopes which have reduced gauge, for gender confirmation and assessment of ovary development.
4.A.2. Materials and Methods
4.A.2.1. Examined fish, anaesthesia and management
Two adult females (Fig. 4.A.1A and 4.A.1B) and two adult males were fasted for 24 hours and then examined on 23rd October 2014 in the DNOCS pisciculture station (Pentecoste-CE, Brazil). Fish were previously PIT tagged and sex evaluated a priori by colour pattern and blood vitellogenin detection (Dugue et al., 2008) and later by endoscopic analysis. Fish total length and weight were 1.53 ± 0.12 m and 32.8 ± 8.5 kg, respectively. Each fish was anaesthetised by spraying MS222 buffered solution onto the gills (200 mg.L-1, Sigma Aldrich), as previously demonstrated in Honczaryk & Inoue (2009) for the air breather A. gigas. For safety reasons and to facilitate the procedure, each fish was contained lying on the left side on a wet soft table. Aerial breathing was stimulated at intervals of 4-6 minutes by repositioning the fish belly down. After the procedure, each fish was held in a recovery tank and water was forced through the gills to flush out anesthetic residues. The study complied with the Brazilian guidelines for the care and use of animals for scientific and educational purposes – DBCA – Concea.
4.A.2.2. Endoscopy
Analyses were done with a medical uretero-renoscope (34 cm x 2.6 mm, 6 ° of angular field, 8-13.5 Charr operating sheath, model 27001L/K, Karl Storz Endoscopy, Tuttlingen, Germany), equipped with a Telecam camera of 1 chip, a 50 watt Hi-Lux light source and a 15″ LCD monitor (200450 01-PT, Tele Pack X, Karl Storz, Tuttlingen, German).
During each examination, a 0.5 L sterile saline bag (0.9 % sodium chloride) was used to flush the system allowing image acquisition and secure endoscope navigation. The saline was connected to the operating sheath with a medical intravenous line. Telescopes and sheaths were sterilized with 70 % ethanol for at least 3 min between each procedure.
Figure 4.A.1. Arapaima gigas. A. Adult female. B. Genital papilla at spawning. C.
Genital papilla at endoscopy: 1-Urinary opening; 2-Gonopore and 3-Anus. Endoscopic images of: D. Urinary channel, E. Urinary bladder, F. Ureter openings. G and H. Left ovary in the coelomic cavity. I. Mature ovary depicting green vitellogenic oocytes (stage III).
4.A.3. Results
Examinations were followed on the monitor screen and recorded for later analyses. As the gonopore is hardly distinguishable from the urinary pore without a guided inspection, the endoscope was essential to reveal their relative position on the genital papilla (Fig.
4.A.1C), and also their different angulation for endoscope navigation. For future guidance, images of the urinary canal, bladder and ureter openings are also presented (Fig. 4.A.1D, E and F). Accessing through the gonopore, the endoscope reached the straight short ligament (“oviduct”) gaining access to the coelomic cavity (Fig. 4.A.1G).
Internal organs could then be observed as well as the left functional ovary (Fig. 4.A.1H and I). Ovary assessment was made within 1-3 min by a trained operator. Following a macroscopic ovary developmental scale proposed in Núñez & Duponchelle (2009), the two females could have their ovary determined at stage 3, with the lamellae containing oocytes at stages II and III (vitellogenic). The fish analysed fully recovered after the procedure with no injury observed in the internal tissues.
4.A.4. Discussion
Given the impossibility of cannulating A. gigas (Núñez et al., 2011), the only method successfully tested so far for maturity identification was through laparoscopy, although it was initially developed for juvenile sex identification (Carreiro et al., 2011). However, such technique is invasive and involves surgery. Due to welfare concerns, it is not applicable to broodstock. The progress made in medical and veterinary endoscopic equipment and their use as a diagnostic tool for sexing and/or assessment of gonadal development is significant for many fish species (Hurvitz et al., 2007; Swenson et al., 2007; Divers, 2010). It is particularly true in A. gigas where traditional methods for
reproductive assessment are not suitable. Such a technique was proved to be useful in this preliminary trial.
The preliminary endoscopic test made so far could have a direct application for farmers and breeders as it enables the identification of maturing females (e.g. late vitellogenesis/final oocyte maturation) within a population. Broodstock management of the species would then be based on informed decisions on couple pairing and it could increase mating and spawning success in farms. This adapted technique could also improve fishery management practices of the species across the Amazon. When dealing with males, the unknown position and gauge of the spermiduct prevented assessing the testis, and further analyses are still required. At this stage, despite the many applications this technical adaptation can have, it will be essential that a more thorough study, under practical operational conditions, be undertaken to evaluate the reliability of the technique before it comes to use by the industry.
CHAPTER 4: PART B