Bighead carp are characterized by many morphological and physiological adaptations that allow them to survive and grow in wide range of environmental conditions. However, information on how this species withstands environmental change is contradictory. To address this issue a set of experiments were conducted with the aim of determining the effects of two major environmental factors (temperature and oxygen saturation) on the growth of bighead carp under laboratory conditions. Small (S; 2.5±0.3g) and large (L; 5.7±0.5g) bighead carp juveniles were reared in temperatures that were gradually increased by 5°C. Overall, environmental factors significantly (P<0.0001) affected specific growth rate (SGR, %/day), feed conversion ratio (FCR), survival (%) and temperature quotient (Q10) of bighead carp.
The change of temperatures and feeding conditions significantly affected the body composition of small and large bighead carp juveniles. The fatty acid compositions (FA) of total lipids (TL), neutral lipids (NL), and polar lipids (PL) were altered from the initial level by the change of temperatures as well as feeding conditions. Fatty acid compositions of NL and PL were subdivided into saturated (SFA), unsaturated (UFA), Omega-3 (n-3) and Omega-6 (n-6) fatty acids, as well as the ratio of n-3: n-6. Overall, the highest SFA content was found at higher temperature and UFA at a lower temperature and they differed significantly (P<0.05).
Hypoxia tolerance of koi and bighead carps were examined under laboratory conditions. Dissolved oxygen concentration was gradually reduced in a 3L volume respirometry flask and measured at 15 min intervals until reaching the threshold levels, aquatic surface respiration (ASR) and loss of equilibrium (LOE). The results indicated that hypoxia tolerance of koi and bighead carps varies depending on the threshold considered (ASR and LOE). The ontogenetic (size) impact in hypoxia tolerance indicates that oxygen consumption from water (WO) and air (AO) are size dependent in bighead carp; large (L, 10.1g) fish reach LOE faster than medium (M, 1.08g) and small (S, 0.22g), but recovered at a higher rate.
The effects of overwinter conditions on the mortality, growth, proximate and mineral compositions as well as fatty acid (FA) compositions of neutral (NL) and polar lipids (PL) were examined on small and large koi and bighead carps. The results showed significant differences in growth, proximate, mineral and FA compositions PL and NL. Poly unsaturated fatty acids (PUFA), especially arachidonic acid (C: 20.4) and eicosapentaenoic acid (C: 20.5) were significantly (P<0.05) higher in bighead carp than in koi carp. Increased proportion of PL (PUFA) by bighead carp may well be an adaptation which preserves membrane fluidity, allowing them to survive longer exposure to low temperatures than koi carp.
Post embryonic rearing of bighead carp larvae was conducted in laboratory conditions for 18 days with four different diets- Artemia, Krill Yeast (KY), Spleen Yeast (SY) and commercial fish diet Otohime A (OA). Specific growth rate, (SGR, %/day) survival (%), and normalized biomass index (NBI) were significantly (P<0.05) higher in the live diet group compared to the formulated and commercial diets. However, feeding a live diet in later development stages may be unfeasible, so the use of formulated diets may be a viable alternative that can be addressed in future research.
Gonadal sex differentiation of bighead carp between the age of 60 and 330 days (40 to 90 mm total length) was examined histologically. Only anatomically differentiated gonads were distinguished whereas cytological differentiation (spermatogoniaor ogonia) was not observed in the individual sizes studied. Electron microscopic observation or antisperm monoclonal antibody are potential tools differentiating the sex of bighead carp juveniles at this size. An immunohitological method would not likely reveal the shape but might reveal tissue, containing the spermatogonia or ogonia-specific epitope if present.