Broodstock conditioning, spawning, embryonic and early larval development of a novel baby clam species for aquaculture in the southeast Pacific: Tawera elliptica (Lamarck, 1818)

Abstract

Tawera elliptica is a small size (baby) clam with an export fishery in southern Chile. The species is dioecious with external fertilization and without sexual dimorphism. The aim of this work was to optimize broodstock conditioning, induce spawning and describe embryonic development until the early larval stage in a hatchery. Broodstock were conditioned at 3 treatments (with/without sand; water circulation) for 48 days. The clams were fed with a mixed diet of macroalgae, with a daily ration of 250,000 cells/ml. Broodstock response was quantified using condition index and gonad development stages (histological techniques). For spawning induction, physical and biological methods were tested. The best response was achieved in males with physical induction. Histological analysis showed that the water circulation system treatment exhibited the highest percentage of maximum maturity. A fertilization ratio of 500:1 sperm:oocyte was used. The incubation was carried out in 3‐L containers with filtered seawater at 10.7 ± 0.9°C without aeration. Observations, measurements and the duration of each embryonic and larval stage were recorded. The oocyte has a prominent gelatinous layer (= jelly coat) that disappears between the gastrula and trochophore stages. The status of the D‐larval stage was reached at 107 h post fertilization with a mean valve length of 91.4 ± 8.9 µm. This is the first record of the complete embryonic development of this baby clam until the early larval stage and the conditioning in a water circulation system for 48 days are suitable for the species.

Effect of Sperm Ratio and Temperature on Fertilization and Early Larval Development of the Surf Clam Mesodesma donacium (Bivalvia:Mesodesmatidae)

“…Embryonic and larval development observed in M. donacium followed the patterns described for bivalve molluscs [ 7 , 17 , 37 , 39 , 44 , 45 , 46 ]. The effect of temperature on the first divisions, the stages of morula, blastula, gastrula and trochophore larva, was observed, with shorter developing times in higher-temperature treatments.…”

“…A concentration of < 200:1 was the most appropriate for the bivalve Tegillarca granosa . In Chilean clams with commercial value, the variation was very high between a ratio of 10:1 for Gari solida [ 37 ], a ratio of 100:1 for Ensis macha [ 38 ] and, finally, a ratio of 500:1 for Tawera elliptica [ 39 ].…”

“…On the other hand, environmental factors, such as temperature, pH and salinity, also play an important role in the feasibility of restocking populations with a high distribution range [ 2 , 12 , 16 , 18 , 23 ]. In this study, the emission of gametes was through the “stripping” method, and comparisons with other species of clams where spontaneous spawning methods [ 22 ], application of desiccation stress and temperature [ 19 , 39 ] or injection of neurotransmitters [ 20 , 21 , 38 ] were used were difficult. Clotteau and Dubé [ 23 ] used the stripping method to obtain the gametes and required a high density of ml −1 oocytes (>10,000) and also a sperm:oocyte ratio > 100:1, which could be indicative that, depending on the type of spawning induction used [ 20 , 21 ], the process may require a greater or lesser ratio of sperm per oocyte and also different densities of oocytes.…”

Spawning induction and embryonic development of the clam Ameghinomya antiqua (King, 1832)

“…In Tawera elliptica and Tivela mactroides the best results have been achieved with biological induction with gonad extract (Reverol et al 2004, Barría et al 2021 and in Venerupis pullastra with desiccation (Cerviño 2011). On the other hand, other authors have used a mix of thermal shock, food and gonadal extract, and a combination of thermal shock and desiccation (Hur et al 2005, Cerviño 2011, Aranda-Burgos et al 2014, Contreras-Guzmán et al 2014.…”

“…The induction to spawning is key in the cultivation of bivalves. Physical stimuli are the most used, among them temperature variation (thermal shock) and biological stimulation using gonadal extracts (Reverol et al 2004, Helm et al 2006, Barría et al 2021. The thermal shock is the less stressful method and induces a successful gametes expulsion (Bustos & Olavarría 2000, Helm et al 2006, Ng et al 2009, Rengel et al 2009, Aranda-Burgos et al 2014, Castillo-Durán et al 2015.…”