Baseline growth of the Trinidad freshwater crab Poppiana dentata () under laboratory conditions

Abstract

Poppiana dentata (Randall, 1840) is widely distributed throughout riverine habitats in Trinidad. However, there is a scarcity of information on the biology of this species. This study provides the first baseline examination that describes growth aspects for P. dentata. Juvenile crabs were obtained from berried females collected in northwest Trinidad. Carapace width (CW), length (CL), moult incident, intermoult period and qualitative aspects were recorded for crabs (N = 23) over 9 months. CW, CL and intermoult period were used to derive percentage size increment, specific growth rate (SGR) and size at structural maturity for both sexes. Growth curves and logistic equations were also generated for each sex. Hatched crabs (< 5 mm CW) underwent rapid hardening after their first moult, indicating a fast turnover of moult cycles. SGR and CW percent increment were also the highest for this initial moult (P < 0.05). CW, CL, intermoult period, size increment and SGR did not differ between sexes (P > 0.05), with logistic equations expressed as CW = 32.81 (1+exp (1.481 ̵ 0.031t))-1 for males and CW = 34.07 (1+exp (1.516 ̵ 0.027t))-1 for females. Yet, breakpoint analyses indicated dissimilar sizes for structural maturity (male: 28.40 mm CW; female: 16.84 mm CW). These patterns reflect a shorter life span for this species in comparison to what has been reported for other trichodactylid relatives. This can have implications for P. dentata populations residing in anthropogenically disturbed habitats; thus, highlighting the need for conservation strategies to ensure preservation of native wild stock.

Sublethal effects of malathion insecticide on growth of the freshwater crab Poppiana dentata (Randall, 1840) (Decapoda: Trichodactylidae)

“…The lack of the ninth and tenth molts in the exposure cohort was especially suggestive of longer intermolt periods, for these molts, and subsequent ones beyond the end of the 5-month monitoring period. These later intermolt periods would have been longer than the corresponding molt periods of the control group (ninth molt: 29 ± 3 days; tenth molt: 42 ± 3 days) and that reported for a baseline group (ninth molt: 33 ± 11 days; tenth molt: 41 ± 8 days) from a previous study (Singh et al, 2020b). The intermolt period of freshwater decapods can be quite sensitive to pesticides; as highlighted by the longer intermolt periods for juveniles of another trichodactylid, T. borellianus, following a 4-month exposure to sublethal concentrations (0.62, 1.25 and 2.50 µg/L) of a chlorpyrifos insecticide, Terminator Ciagro® (Montagna, 2010), and the irregular intermolt periods of the freshwater prawn, Pa. argentinus, from exposure to low concentrations of chlorpyrifos (0.005-0.022 µg/L) and endosulfan (0.122-0.488 µg/L) insecticides (Montagna and Collins, 2007).…”

“…This period was selected using a prior baseline study on P. dentata, which yielded breakpoint sizes at structural reproductive maturity of 16.84 mm CW (female) and 28.40 mm CW (male). The 5-month period was selected based on the length of time for male crabs to reach a size of 28.75 ± 2.98 mm CW (Singh et al, 2020b).…”

“…The regime involved crabs of CW < 5 mm being fed 2 g of pellets and 2 g of E. densa segments, CW ≥ 5-15 mm were fed 5 g of the pellets and 4 g of E. densa segments, CW > 15-25 mm were fed 10 g of pellets and 6 g of E. densa plant segments, and CW > 25 mm were fed 24 g of pellets and 6 g of E. densa segments. This diet and regime were considered suitable for proper growth since it was similarly applied in the prior, baseline growth study (Singh et al, 2020b) in which crabs were observed to exhibit normal growth and behavior. Removal of uneaten food and feces was performed along with renewal of test water.…”