Juvenile Southern Flounder Paralichthys Lethostigma Research Articles

Evaluation of genetically-improved (glandless) and genetically-modified low-gossypol cottonseed meal as alternative protein sources in the diet of juvenile southern flounder Paralichthys lethostigma reared in a recirculating aquaculture system

Cottonseed meal (CSM) proteins from genetically-improved (glandless) low-gossypol seed (GI-CSM, 52.1% crude protein, CP), genetically-modified low-gossypol seed (GMO-CSM, 56.0% CP) and from an untreated regular (glanded) seed (R-CSM 49.9% CP) were evaluated to replace fish meal (FM) protein (59.5% CP) in juvenile southern flounder Paralichthys lethostigma diets. Eight isonitrogenous (45% CP) and isolipidic (16% crude lipid, CL) diets were formulated. A control diet (0% CSM) contained 40% fishmeal (FM) and other practical protein sources. Six diets replaced 50, 75 and 100% FM protein with GI-CSM or GMO-CSM protein. One diet replaced 100% FM protein by R-CSM protein. Fifteen fish (mean = 1.81 g) were stocked in each of twenty-four 75-L tanks (N = 3 per treatment) and were fed the treatment diets for eight weeks. Final percent weight gain was not significantly (P > 0.05) different in fish fed the GI- and GMO- and R-CSM protein diets (898–1405%) compared with the control diet (0% CSM) (1242%), but percent weight gain was greater (P < 0.05) in fish fed the 50% GI-CSM diet (1405%) versus the 100% GI-CSM diet (898%). Feed conversion ratio was excellent for all treatments (FCR = 0.70–1.00), with no treatment differences (P < 0.05). Protein efficiency ratios (PER) were also not significantly different among the treatments (2.26–3.24), although the lowest value was for 100% R-CSM diets. After 8 weeks of feeding, survival of fish ranged from 80 to 91%, with no treatment differences. Apparent protein digestibility of diets was significantly higher for the fish fed 75% and 100% GI-CSM and 100% GMO-CSM protein diets (83.5, 83.5 and 86.5%, respectively) compared with the control diet (79.4%). After 8 weeks, no significant (P > 0.05) interactive effects between CSM sources and FM replacement levels on final weight, FCR and PER were observed. Arginine levels in the diets increased as CSM was increased, consistent with the high arginine concentrations found in CSM. Liver gossypol was only detectable in fish fed the 100% R-CSM diet (37 μg/g). Replacing up to 75% FM protein by GI- or GMO-CSM protein did not affect on whole body omega-3 PUFAs, or liver gossypol. The results suggest that up to 75% of fish meal protein may be replaced by GI- or GMO-CSM protein in the diet of juvenile flounder without adverse effects on growth performance and body composition. Statement of relevanceCottonseed meal (CSM) is a potentially cost-effective alternative plant protein source for use in aquafeeds. The results suggest that a 75% of fishmeal protein could be replaced by genetically-improved and genetically modified (GMO) low gossypol based cottonseed flour protein in the diet of southern flounder. These ultra-low gossypol cottonseed flour proteins could be inexpensive protein sources for the commercial culture of southern flounder and other finfish species.

Fine‐scale movements and habitat use of juvenile southern flounder Paralichthys lethostigma in an estuarine seascape

Habitat use of juvenile southern flounder Paralichthys lethostigma was examined within a shallow estuarine seascape during June and July 2011 using acoustic telemetry. Fine-scale movement and habitat use of P. lethostigma was investigated with an acoustic positioning system placed in a seascape that varied in habitat type, physicochemical conditions and bathymetry. The use of different habitat types was examined with Euclidean distance-based analyses, and generalized additive models were used to determine the relative importance of habitat type relative to physicochemical conditions and bathymetry. Tracks of P. lethostigma ranged in distance between 1477 and 8582 m and speed was 4·2 ± 1·1 m min⁻¹ (mean ± s.e.) for all P. lethostigma combined. Depth, slope and habitat type had the most influence on P. lethostigma occurrence and deep sandy areas with shallow slopes were used most frequently. In addition, depth use by P. lethostigma was influenced by tidal cycles, indicating habitat use varies temporally and is dynamic. Finally, temperatures <30·5° C were used more than warmer waters within the study area. The results successfully identify movements by juvenile P. lethostigma, and indicate that definitions of essential habitats need to account for dynamics in habitat use.

Comments on Lowe et al. “Otolith Microchemistry Reveals Substantial Use of Freshwater by Southern Flounder in the Northern Gulf of Mexico”

Lowe et al. (Estuaries and Coasts, 34:630–639, 2011) hypothesized that juvenile southern flounder Paralichthys lethostigma (Jordan and Gilbert 1884) would migrate from the Gulf of Mexico into the Mobile-Tensaw River Delta (AL, USA) and use low-salinity (oligohaline/freshwater) habitats during, at least, a portion of their first year of life. Thus, they analyzed the Sr/Ca ratio profiles along the sagittal otoliths of southern flounder collected in the Mobile-Tensaw River Delta and observed that one third of the flounders had low Sr/Ca levels in the otoliths’ core and throughout the otolith, suggesting that these fishes hatched in freshwater or low-salinity habitats where they spend the majority of their life. The other two thirds of southern flounder showed high levels of Sr/Ca ratio in the otoliths’ core following a marked decline of Sr/Ca ratio, which then maintained along the remainder of the otolith. This pattern was interpreted as larvae hatched in higher salinity waters before entering the Mobile-Tensaw River Delta; however, in this paper, I list several arguments to support an alternative interpretation for this pattern. I suggest that the high levels of Sr/Ca ratios in the otoliths’ core of southern flounder does not reflect the saline conditions where larvae hatched, instead it reflects the location where the female progenitor hydrated the eggs. Thus, adding my interpretation on the data of Lowe et al. (Estuaries and Coasts, 34:630–639, 2011), it seems that southern flounder might hatch in or near freshwater habitats and the migration of southern flounder into an estuarine ecosystem to spawn might exist.

Effects of Replacement of Menhaden Fish Meal Protein by Solvent‐Extracted Soybean Meal Protein Supplemented with or without l‐Methionine and l‐Lysine in the Diet of Juvenile Southern Flounder

AbstractTwo feeding experiments were conducted to study the effects of different levels of solvent‐extracted soybean meal on the growth and body composition of juvenile southern flounder Paralichthys lethostigma. In experiment 1, seven diets were formulated, replacing menhaden fish meal protein (FMP) with soybean meal protein (SBP) at 0, 10, 20, 30, 40, 50, and 60% without supplementing amino acids. In experiment 2, eight diets were formulated, replacing FMP with SBP at 0, 10, 20, 30, 40, 50, 60, and 70% and supplementing with l‐methionine and l‐lysine. In the test diets, l‐methionine and l‐lysine were supplemented to approximate the methionine and lysine level found in the 45% whole‐body protein of southern flounder. All diets were formulated to have the same crude protein (45%) and lipid levels (12%), and all diets contained 9% squid meal and 5% krill meal to improve palatability. Each of the test diets was fed two times a day to triplicate groups of flounder (average weight = 0.61 g for experiment 1 and 1.63 g for experiment 2). Experiments 1 and 2 were conducted for 42 and 60 d, respectively. Fish were held in 75‐L recirculating seawater tanks at 15 fish per tank. In both experiments, no significant differences were observed in body weight gain (WG), specific growth rate, feed intake, feed conversion and protein efficiency ratios, and the whole‐body proximate composition among fish fed diets replacing 0–40% of FMP with SBP. When compared with fish fed 0% SBP, WG decreased significantly for the fish fed more than 40% SBP. Broken‐line regression showed that the optimum levels of FMP replacement with SBP in the diet of southern flounder without and with supplemental methionine and lysine were 35.1% and 38.9%, respectively, when diets contained 9% squid meal and 5% krill meal.